THE PHOTOPHYSICAL PROPERTIES OF MULTIPLY BONDED METAL
COMPLEXES OF MOLYBDENUM, TUNGSTEN, AND RHENIUM
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy
in the Graduate School of The Ohio State University
By
Carly R. Reed, B.A.
Graduate Program in Chemistry
The Ohio State University
2011
Dissertation Committee:
Professor Malcolm H. Chisholm, Advisor
Professor Claudia Turro, Advisor
Professor Terry L. Gustafson
Copyright by
Carly R. Reed
2011
ABSTRACT
Rhenium dimetal complexes have been synthesized where the bond order between
the metal atoms ranges from four in Re26+ complexes (242) to three in Re24+
complexes (242*2). Re2(O2CC6H4-p-NO2)4Cl2 was prepared by reacting
Re2(O2CCH3)4Cl2 with p-nitrobenzoic acid in refluxing methanol. Re2(dppm)2(O2CC6H4p-NO2)2Cl2 was prepared by the reaction between Re2(dppm)2(O2CCH3)2Cl2 and pnitrobenzoic acid in refluxing methanol The effects on the electrochemical and
photophysical properties as the metal core is changed have been explored. Calculations
reveal that in the Re26+ complex the HOMO is Re2  and the LUMO is Re2 *. In the
Re24+ complex, the HOMO is Re2 * and the LUMO is Re2 * with some nitrobenzoate
ligand * character. In both complexes the orbital lies below the HOMO and the M2 
to benzoate * metal-to-ligand charge transfer (MLCT) transition occurs at ~350 nm.
Since this is not the lowest energy transition in either complex they are both dull orangebrown in color. The Re26+ complex possesses an emissive 3* state as its lowest energy
triplet state, similar to Mo24+, and some W24+ complexes. The
Re2(dppm)2(O2CC6H4NO2)2Cl2 complex possesses one short lived excited state ( = 1.6
ps) and a long lived excited state ( = 2-10 ns). Based on the appearance of the transient
absorption, the longer lived excited state in Re2(dppm)2(O2CC6H4NO2)2Cl2 may have
some ligand character.
ii
A new series of quadruply bonded dimetal tetracarboxylate complexes has been
synthesized with the formula, M2(TiPB)2(O2CCH=CHTh)2 and M2(TiPB)2(O2CC≡CTh)2
where M = Mo or W, TiPB = 2,4,6-triisopropylbenzoate, and Th = thienyl by reacting
M2(TiPB)4 with two equivalents of 3-(2-thienyl)acrylic acid or 3-(2-thienyl)propynoic
acid in toluene. Calculations and electrochemistry reveal that the O2CC≡CTh ligand
stabilizes the M2 HOMO by ~0.20-0.24 V (calculated, 0.23 eV) compared to the
O2CCH=CHTh ligand.
All four complexes are intensely colored due to the M2 
(HOMO) to thienyl carboxylate ligand * (LUMO) charge transfer transition that occurs
in the visible region. The energy of the MLCT transition also reflects the stabilization of
the HOMO where the max of the M2(TiPB)2(O2CCH=CHTh)2 complexes are shifted by
1500-2000 cm-1 to lower energies compared to the M2(TiPB)2(O2CC≡CTh)2 complexes.
The intensity of the vibronic features that appear in the MLCT absorption band of the
M2(TiPB)2(O2CCH=CHTh)2 complexes at 100 K reveal the increased electronic coupling
of the O2CCH=CHTh ligands through the dimetal center when M = W compared to when
M = Mo.
A further series of quadruply bonded dimetal tetracarboxylate complexes has been
synthesized with the formula, M2(TiPB)2(O2CC≡CAr)2 where M = Mo or W, TiPB =
2,4,6-triisopropylbenzoate, and Ar = tolyl or anthracenyl by reacting M2(TiPB)4 with two
equivalents of 3-(4-tolyl)propynoic acid or 3-(9-anthracenyl)propynoic acid in toluene.
Calculations reveal that in all four complexes the HOMO is the M2  orbital and the
LUMO is an in-phase combination of the the arylethynyl carboxylate * orbitals. The
energy of the HOMO is mainly depended on the nature of the metal atom, with the
tungsten complexes being easier to oxidize compared to the molybdenum analogues by ~
iii
0.5 eV, however, these complexes also show that the  donating ability of the ligand is
important where the filled anthracenyl  orbitals are closer in energy to the the M2  and
therefore destabilize the HOMO by ~ 0.10 eV compared to the tolyl analogues. All four
complexes exhibit solvent dependent HOMO to LUMO MLCT transitions in the visible
region as their lowest energy transitions, resulting in brightly colored complexes.
Fluorescence has also observed in these complexes from the 1MLCT state. The excited
states of all four complexes have been investigated with femtosecond transient absorption
where they are seen to quickly intersystem cross from their 1MLCT state to a longer lived
triplet state on the ps timescale. Both molybdenum complexes possess an emissive 3*
state ( = 86-101 s) that is solvent independent and exhibits vibronic features matching
the ground state (MM). Femtosecond and nanosecond transient absorption reveal that
the tungsten complexes possess shorter triplet states with  = 3-10 ns, indicating 3MLCT
rather than 3* excited states.
The triplet state of W2(TiPB)2(O2CC≡CTolyl)2 is
emissive with max ~ 875 nm in THF, while W2(TiPB)2(O2CC≡CAnthracenyl)2 has a
nonemissive triplet state. The femtosecond time resolved infrared spectroscopy (fsTRIR) of the complexes where the (C≡C) was monitored are discussed.
In
W2(TiPB)2(O2CC≡CTolyl)2 a (C≡C) signal remains in the triplet state confirming the
MLCT nature.
The fact that a signal was not observed in the triplet state of
W2(TiPB)2(O2CC≡CAnthracenyl)2 may be due to weak signal intensity. A larger ground
to 1MLCT excited state shift of the of W2(TiPB)2(O2CC≡CTolyl)2 (C≡C) signal to lower
energy indicates the electron density is more localized on the C≡C portion of the ligand
compared
to
the
W2(TiPB)2(O2CC≡CAnthracenyl)2
iv
complex.
To my family: Scott, Debbie, and Jared Reed
v
ACKNOWLEDGEMENTS
While the cover of this dissertation bears my name, there are people without
whom it would not have been possible.
First, my advisors, Prof. Malcolm Chisholm and Prof. Claudia Turro. I have been
truly blessed to have had the opportunity to work for them. They have inspired me with
their excitement and dedication to chemistry. They have offered me patience, guidance,
and a genuine interest in my success and happiness. I could not have asked for more
supportive, knowledgeable, self-sacrificing, and fun advisors.
To my labmates I also owe a great deal of thanks. Thanks to Brian Alberding for
the countless hours spent in the basement running all of the femtosecond time resolved
experiments. Thanks to Samantha Brown for contributing the Mo2(O2CH)2(O2CTh)2
calculations discussed in Chapter 3.
Thanks to Yao Liu for training me to use the
nanosecond transient absorption and NIR emission instruments.
Thanks to Dr.
Yagnaseni Ghosh, my Guru, for training me in the lab and never tiring of my questions.
And thanks to all my other labmates and fellow graduate students who discussed
chemistry with me and made life enjoyable.
I would also like to offer a special acknowledgement to my family, whose
unconditional love and support has given me the courage to try things that seemed to be
impossible. Mom and Dad, thank you for your endless sacrifices in order to see me
succeed in this life and for always believing in me. I probably wouldn't be a scientist
today if my father, Scott Reed, had not conducted homemade experiments and shared
vi
Discover magazines with me. And I could not have made it this far without the example
of perseverance and success provided by my mother, Debbie Reed.
And last but not least, I want to acknowledge my wonderful friends, whose love
and support mean more than I can express in words. Thank you to Kate and Andy for the
late night study sessions and lots of laughs. Yagnaseni Ghosh, Sandeep Kumar, Shana
Lear, and Ben Lear thank you for always welcoming me into your homes, knowing just
what to say, and providing wonderful examples on how to live life as a graduate student.
Kellyann, Molly, and Zack Wiles thanks for your constant support and faith, as well as
countless meals. I hope I can repay you with many lobster dinners someday. And
finally, to Megan, Dawn, and Dave Elliott, you have been my home during these years in
graduate school and I doubt I will ever be able to repay you for your unconditional love,
support, and comic relief.
vii
VITA
2008-Present………………………………Research Assistant, The Ohio State University
2005-2008…………………………………Teaching Assistant, The Ohio State University
2000-2005…………………………………………….....B.A. Chemistry, Malone College
PUBLICATIONS
and Re26+ carboxylate compounds.
Alberding, B.G.; Chisholm, M.H.; Gallucci, J. C.; Gustafson, T.L.; Carly R. Reed,
Turro, C. Dalton Trans. (2010), 39 (48), 11587-11593.
1. Concerning the photophysical properties of Re2
4+
2. Oxalate bridged triangles incorporating Mo24+ units. Electronic structure and bonding.
Chisholm, M.H.; Patmore, N.J.; Carly R. Reed; Singh, N. Inorg. Chem. (2010), 49
(15), 7116-7122.
3. Molecular, electronic structure and spectroscopic properties of MM quadruply
bonded units supported by trans-6-carboethoxy-2-carboxylatoazulene ligands.
Alberding, B.G.; Barybin, M. V.; Chisholm, M.H.; Gustafson, T. L.; Patmore, N.J.;
Carly R. Reed, Robinson, R.E.; Singh, N.; Turro, C. Dalton Trans. (2010), 39 (8),
1979-1984.
4. Quadruply Bonded Dimetal Units Supported by 2,4,6-Triisopropylbenzoates
MM(TiPB)4 (MM = Mo2, MoW, and W2): Preparation and Photophysical Properties.
Alberding, B.G.; Chisholm, M.H.; Chou, Y-H.; Gallucci, J.C.; Ghosh, Y.; Gustafson,
T.L.; Patmore, N.J.; Carly R. Reed; Turro, C. Inorg. Chem. (2009), 48, 4394-4399.
5. [Bis(trispivalatodimolybdenum(II))-bis(4’-carboxylato-2,2’:6’,2”terpyridine)ruthenium(II)](2+) Tetrafluoroborate: Photophysical Studies. Alberding,
B.G.; Chisholm, M.H.; Gustafson, T.L.; Carly R. Reed; Singh, N.; Turro, C. J. Clust.
Sci. (2009), 20, 307-317.
FIELDS OF STUDY
Major Field: Chemistry
viii
TABLE OF CONTENTS
Abstract……………………………………………………………………………………ii
Dedication………………………………………………………………………………...v
Acknowledgements………………………………………………………………………vi
Vita…………………………………………………………………………………...…viii
List of Tables…………………………………………………………………………....xiii
List of Figures…………………………………………………………………………...xiv
List of Abbreviations………………………………………………………………..…xviii
CHAPTERS
1
INTRODUCTION ....................................................................................................... 1
1.1
Introduction .............................................................................................................. 1
1.2
Multiple Bonds Between Metal Atoms.................................................................... 2
1.3
Paddlewheel Complexes .......................................................................................... 5
1.4
Absorption of Light by Molecules ........................................................................... 7
1.5
Excited State Decay Pathways ............................................................................... 10
1.6
Breakdown of Selection Rules ............................................................................... 14
1.7
Absorption of Quadruply Bonded Metal Complexes ............................................ 16
1.8
Emission of Quadruply Bonded Metal Complexes ............................................... 19
1.9
Statement of Purpose ............................................................................................. 23
2 PHOTOPHYSICAL PROPERTIES OF Re24+ AND Re26+ CARBOXYLATE
COMPOUNDS ................................................................................................................. 25
ix
2.1
Introduction ............................................................................................................ 25
2.2
Synthesis ................................................................................................................ 26
2.3
Molecular and Single Crystal Structure of cis-Re2(dppm)2(O2CC6H4-p-NO2)2Cl2
……………………………………………………………………………………………27
2.4
Electronic Absorption Spectra ............................................................................... 30
2.5
Electronic Structure Calculations .......................................................................... 32
2.6
Electrochemical Studies ......................................................................................... 42
2.7
Emission Spectra .................................................................................................... 44
2.8
Transient Absorption Spectroscopy ....................................................................... 45
2.9
Conclusion ............................................................................................................. 47
2.10
Experimental Section ............................................................................................. 48
2.11
2.10.1
Materials and Methods ................................................................................ 48
2.10.2
Computational Methods .............................................................................. 50
2.10.3
X-ray Crystallography ................................................................................ 50
2.10.4
Synthesis ..................................................................................................... 51
Acknowledgements ................................................................................................ 53
3 COMPARISON OF ELECTRONIC AND PHOTOPHYSICAL PROPERTIES OF
QUADRUPLY BONDED DIMETAL COMPLEXES WITH THIENYL ETHYNYL
CARBOXYLATE AND THIENYL VINYL CARBOXYLATE LIGANDS .................. 54
3.1
Introduction ............................................................................................................ 54
3.2
Synthesis ................................................................................................................ 55
3.3
Electronic Absorption Spectra ............................................................................... 56
3.4
Electronic Structure Calculations .......................................................................... 57
x
3.5
Electrochemical Studies ......................................................................................... 64
3.6
Variable Temperature Absorption ......................................................................... 67
3.7
Emission Studies .................................................................................................... 70
3.8
Solvent Dependence............................................................................................... 71
3.9
Conclusions ............................................................................................................ 73
3.10
Experimental .......................................................................................................... 73
3.10.1
Materials and Methods ................................................................................ 73
3.10.2
Computational Methods .............................................................................. 75
3.10.3
Synthesis ..................................................................................................... 75
4 THE ELECTRONIC AND PHOTOPHYSICAL PROPERTIES OF QUADRUPLY
BONDED DIMETAL COMPLEXES SUPPORTED BY
ARYLETHYNYLCARBOXYLATE LIGANDS ............................................................ 78
4.1
Introduction ............................................................................................................ 78
4.2
Syntheses................................................................................................................ 79
4.3
Single Crystal Structure of 1a [Mo2(TiPB)2(O2CC2C6H4CH3)2∙4THF] ................. 80
4.4
Electronic Structure Calculations .......................................................................... 83
4.5
Electrochemical Studies ......................................................................................... 86
4.6
Electronic Absorption ............................................................................................ 87
4.7
Temperature Dependence of Absorbance .............................................................. 92
4.8
Emission................................................................................................................. 97
4.9
Solvent Dependence of Emission ........................................................................ 100
4.10
Transient Absorption ........................................................................................... 103
4.11
Time Resolved Infrared Spectroscopy ................................................................. 112
xi
4.12
Conclusions .......................................................................................................... 117
4.13
Experimental Section ........................................................................................... 118
4.13.1
X-Ray Crystallography ............................................................................. 118
4.13.2
Materials and Methods .............................................................................. 119
4.13.3
Computational Methods ............................................................................ 122
4.13.4
Synthesis ................................................................................................... 123
APPENDICES:
Appendix A: Crystalligraphic data for Re2(dppm)2(O2CC6H4NO2)2Cl2·2 THF and
Mo2(TiPB)2(O2CC2C6H4CH3)2∙4 THF………………………………………………….133
Appendix B: Spectroscopic data for Mo2(TiPB)2(O2CC2C6H4CH3)2,
W2(TiPB)2(O2CC2C6H4CH3)2, Mo2(TiPB)2(O2CC2-9-C14H9)2, W2(TiPB)2(O2CC2-9C14H9)2……………………………………………………………….…………………173
BIBLIOGRAPHY………………………………………………………………………177
xii
LIST OF TABLES
Table 1.1 Quadruply bonded M2 complexes exhibiting* transitions. ..................... 18
Table 2.1 Crystallographic data for Re2(dppm)2(O2CC6H4NO2)2Cl2 · 2 THF. ................ 29
Table 2.2 Select bond distances for Re2(dppm)2(O2CC6H4NO2)2Cl2.* ........................... 30
Table 2.3 Orbital contributions of electronic transitions of
Re2(dppm)2(O2CC6H4NO2)2Cl2 singlet ground state. ....................................................... 37
Table 2.4 Orbital contributions of electronic transitions of Re2(O2CC6H4NO2)4Cl2 singlet
ground state. H = HOMO, L = LUMO. ........................................................................... 41
Table 2.5 Electrochemical oxidation and reduction potentials of
compounds in THF versus Cp2Fe0/+ couple. ..................................................................... 43
Table 3.1 Electrochemical Potentials and Calculated Energies ....................................... 59
Table 3.2 Orbital contributions of transitions of singlet ground state of
(a) Mo2(O2CH)2(O2CC≡CTh)2 (b) Mo2(O2CH)2(O2CCH=CHTh)2
(c) W2(O2CH)2(O2CC≡CTh)2 (d) W2(O2CH)2(O2CCH=CHTh)2 .................................... 63
Table 4.1 Crystallographic details for Mo2(TiPB)2(O2CC2C6H4CH3)2∙4THF ................. 82
Table 4.2 Oxidation and reduction potentials of complexes 1a, 2a, 1b,
and 2b in 0.1M Bu4NPF6/THF solution versus internal standard FeCp20/+. ..................... 87
Table 4.3 Room temperature and low temperature absorption and emission data of 1a,
2a, 1b, and 2b in 2-MeTHF. ............................................................................................. 99
Table 4.4 Solvent dependence of absorption and emission of 1a, 2a, 1b, 2b................. 102
Table 4.5 Summary of the excited state dynamics and ground and excited state IR
frequencies. ..................................................................................................................... 117
xiii
LIST OF FIGURES
Figure 1.1 Image of the structure of [Re2Cl8]2- ion in K2Re2Cl8•2H2O.. ........................... 3
Figure 1.2 Interactions between d orbitals during formation of the quadruple bond......... 4
Figure 1.3 The basic structure of a paddlewheel complex ................................................. 5
Figure 1.4 (a) Synthetic route to bis-bis heteroleptic dimetal complexes, where M = Mo,
and W, R = 2,4,6-triisopropylbenzoate. (b) Synthetic route to cis heteroleptic dirhenium
paddlewheel complex with carboxylate and dppm ligands, where R = methyl and dppm =
bis(diphenylphosphino)methane. Modified from reference 19 and 20. ............................. 7
Figure 1.5 Left: Representation of molecule with distinct vibrational substates. Right:
Absorption and emission spectra with vibrational structures. Reproduced from ref 23. .. 10
Figure 1.6 Simplified state energy diagram displaying transition pathways between
states. Modified from reference 23. ................................................................................ 12
Figure 1.7 Jablonski diagram of [Cr(acac)3]. Reproduced from reference 24. ............... 13
Figure 1.9 Diagram depicting orbital interactions between formamidinate ligand 
orbitals and metal-metal orbitals. Reproduced from reference 47. .................................. 20
Figure 1.10 Absorption (THF, r.t.) and near-IR emission spectra (2-MeTHF, 77K) of
M2(TiPB)4 complexes. Mo2 (red), MoW (blue), W2 (green). Reproduced from reference
16....................................................................................................................................... 22
Figure 2.1 ORTEP drawing of Re2(dppm)2(O2CC6H4NO2)2Cl2 drawn with 50%
probability ellipsoids. Hydrogen atoms are omitted for clarity. The solvent molecule of
THF is shown here. The Re complex contains a crystallographic two-fold rotation axis.
........................................................................................................................................... 28
Figure 2.2 Absorption spectrum of Re2(dppm)2(O2CC6H4NO2)2Cl2 in CH2Cl2. Inset:
Magnified view of absorption spectrum in region 450 – 1000 nm. .................................. 31
Figure 2.3 Absorption spectrum of Re2(O2CC6H4NO2)4Cl2 in THF. .............................. 32
Figure 2.4 Energy diagram of frontier orbitals of Re2(dppm)2(O2CR)2Cl2 (isovalue =
0.03). ................................................................................................................................. 34
xiv
Figure 2.5 Absorption spectra of Re2(dppm)2(O2CC6H4NO2)2Cl2 in CH2Cl2 and
calculated electronic transitions of singlet ground state. (Top) is an enlarged view of
bottom spectrum from 400-1000 nm. ............................................................................... 36
Figure 2.6 Calculated orbitals of Re2(dppm)2(O2CC6H4NO2)2Cl2 involved in transitions
that are not shown in Figure 2.5........................................................................................ 37
Figure 2.7 Guassview plot of the optimized ground state structure of
Re2(O2CC6H4NO2)4Cl2 with Ci symmetry........................................................................ 38
Figure 2.8 Energy diagram showing frontier orbitals of Re2(O2CC6H4NO2)4Cl2 ground
state (isovalue = 0.03). ...................................................................................................... 39
Figure 2.9 Absorption spectra of Re2(O2CC6H4NO2)4Cl2 in THF and calculated
electronic transitions of singlet ground state. ................................................................... 41
Figure 2.10 Calculated orbitals of Re2(O2CC6H4NO2)4Cl2 involved in transitions that are
not shown in Figure 2.8. ................................................................................................... 42
Figure 2.11 Differential pulse voltammagrams of Re2(dppm)2(O2CR)2Cl2 in THF where
R = CH3 (orange) and R = C6H4NO2 (blue). Potentials are reported versus the Cp2Fe0/+
couple. ............................................................................................................................... 43
Figure 2.12 Near-IR emission spectrum of Re2(O2CC6H4NO2)4Cl2 in 2-Me-THF at 77K
(exc = 405 nm). ............................................................................................................... 44
Figure 2.13 fs-TA broadband spectrum of Re2(dppm)2(O2CCH3)2Cl2 in THF (exc = 365
nm). Kinetic trace at 4125 nm shows  = 2.3 ± 0.1 ps. .................................................... 46
Figure 2.14 fs-TA broadband spectrum of Re2(dppm)2(O2CC6H4NO2)2Cl2 in THF (exc =
365 nm). Kinetic trace at 415 nm shows = 1.6 ± 0.2 ps. ................................................ 46
Figure 3.1 Synthetic route to heteroleptic bis-bis dimetal complexes. ............................ 56
Figure 3.2 Electronic absorption spectra of Mo2(TiPB)2(O2CC≡CTh)2, max = 476 nm
(orange); Mo2(TiPB)2(O2CCH=CHTh)2, max = 515 nm (red); W2(TiPB)2(O2CC≡CTh)2
max = 646 nm (blue); and W2(TiPB)2(O2CCH=CHTh)2, max = 750 nm (green) in THF
at room temperature. ......................................................................................................... 57
Figure 3.3 Calculated energy diagram of frontier orbitals of M2(O2CH)2(O2CC≡CTh)2
and M2(O2CH)2(O2CCH=CHTh)2, where M = Mo, W. ................................................... 61
Figure 3.4 Molecular orbital plots of frontier orbitals for M2(O2CH)2(O2CC≡CTh)2 and
M2(O2CH)2(O2CCH=CHTh)2, where M = Mo, W; isosurface value of 0.02. .................. 62
xv
Figure 3.5 Oxidation DPVs of complexes Mo2(TiPB)2(O2CC≡CTh)2 (orange),
Mo2(TiPB)2(O2CCH=CHTh)2 (red), W2(TiPB)2(O2CC≡CTh)2 (blue),
W2(TiPB)2(O2CCH=CHTh)2 (green) in 0.1M Bu4NPF6/THF solution. Referenced versus
Cp2Fe0/+ redox couple. ...................................................................................................... 65
Figure 3.6 Cyclic voltammagrams of M2(TiPB)2(O2C-CH=CHTh)2, M = Mo (red) and W
(green) in 0.1M Bu4NPF6/THF solution with respect to Cp2Fe0/+ couple. M = Mo:
E1/2RED(1) = -2.449 V, E1/2RED(2) = -2.618 V; M = W: E1/2RED(1) = -2.378 V; E1/2RED(2) = 2.723 V.............................................................................................................................. 67
Figure 3.7 Potential energy surfaces representing the ground state (S0) and mixed
valence excited state (S1) in a weakly coupled Class II system (left), a system on the
Class II/III border (center), and in a completely delocalized Class III system (right)...... 68
Figure 3.8 Electronic absorption spectra in 2-MeTHF of Mo2(TiPB)2(O2CCH=CHTh)2 at
room temperature (red dashed) and -174oC (red solid) and W2(TiPB)2(O2CCH=CHTh)2 at
room temperature (green dashed) and -175oC (green solid). ............................................ 70
Figure 3.9 Visible (exc = 460 nm) and NIR (exc = 405nm, 785 nm) emission spectra of
Mo2(TiPB)2(O2CCH=CHTh)2 (red) and W2(TiPB)2(O2CCH=CHTh)2 (green) in THF. .. 71
Figure 3.10 Absorption (dashed lines) and emission (solid lines) of
Mo2(TiPB)2(O2CCH=CHTh)2 in various solvents, CHCl3 (blue), CH2Cl2 (green), THF
(red), and DMSO (black). ................................................................................................. 72
Figure 4.1 Synthetic route to heteroleptic bis-bis dimetal complexes, where R' represents
C≡C-p-tolyl or C≡C-9-anthracenyl. .................................................................................. 80
Figure 4.2 ORTEP drawing of Mo2(TiPB)2(O2CC2C6H4CH3)2∙4THF (1a) drawn with
50% probability ellipsoids. Hydrogen atoms are omitted for clarity. The solvent
molecules of THF are shown here. The Mo complex contains an inversion center. ....... 81
Figure 4.3 Energy diagram displaying the calculated energies of the frontier orbitals of
the ground states of 1a, 1b, 2a, and 2b. 1a and 1b were optimized in C2 symmetry and 2a
and 2b were optimized in D2h symmetry. ......................................................................... 83
Figure 4.4 Frontier orbitals of the ground states of 1a, 1b, 2a, and 2b. 1a and 1b were
optimized in C2 symmetry and 2a and 2b were optimized in D2h symmetry. Note: W2 
orbitals of 1b not shown; energetically these orbitals are between the filled ligand  and
W2 . ................................................................................................................................. 84
Figure 4.5 Interactions between  orbital on the dimetal unit and the filled ligand 
obritals as well as the ligand * orbitals. Modified from reference 95. ........................... 85
Figure 4.6 Absorption spectra of 1a (orange), 2a (red), 1b (blue), and 2b (green) in THF.
........................................................................................................................................... 89
xvi
Figure 4.7 Experimental normalized absorption spectra in THF of 1a (orange), 2a (red),
1b (blue), and 2b (green) plotted with the time-dependent calculated transitions of in the
gas phase. .......................................................................................................................... 90
Figure 4.8 Normalized room temperature absorbance of (Left) 1b and (Right) 2b.
Chloroform (purple), dichloromethane (blue), benzene (green), THF (black), and DMSO
(red). .................................................................................................................................. 92
Figure 4.9 Potential energy surfaces representing the ground state (S0) and mixed
valence excited state (S1) in a weakly coupled Class II system (left), a system on the
Class II/III border (center), and in a completely delocalized Class III system (right)…...93
Figure 4.10 (Top) Room temperature (dashed line) and low temperature absorption
(100K, solid line) of 1a (orange) and 1b (blue) in 2-MeTHF. (Bottom) Room temperature
(dashed line) and low temperature absorption (100K, solid line) of 2a (red) and 2b
(green) in 2-MeTHF. ......................................................................................................... 96
Figure 4.11 Low temperature absorption (100K, dashed line) and emission spectra (77K,
solid line) of 1a (orange) and 1b (blue) in 2-MeTHF. ...................................................... 98
Figure 4.12 Low temperature absorption (100K, dashed line) and emission spectra (77K,
solid line) of at 2a (red) and 2b (green) in 2-MeTHF....................................................... 98
Figure 4.13 Normalize emission of 1b in chloroform (purple), dichloromethane (blue,
RT), benzene (green, RT), THF (black, RT), 2-MeTHF (black dashed, 77K), and DMSO
(red, RT). ......................................................................................................................... 101
Figure 4.14 Femtosecond transient absorption of 2a in THF, exc = 514 nm. ............... 104
Figure 4.15 Nanosecond transient absorption of 2a in THF, exc = 532 nm. ................. 105
Figure 4.16 Nanosecond transient absorption of 1a in THF, exc = 355 nm. ................. 106
Figure 4.17 Femtosecond transient absorption of 1b in THF, exc = 514 nm. ............... 109
Figure 4.18 Femtosecond transient absorption of 2b in THF, exc = 675 nm. ............... 110
Figure 4.19 Nanosecond transient absorption of 1b and 2b in THF, exc = 532 nm. ..... 111
Figure 4.20 Jablonski diagram summarizing the photophysical properties of 1a (orange),
2a (red), 1b (blue) and 2b (green). ................................................................................. 112
Figure 4.21 fs-TRIR of 1b (top) and 2b (bottom). ......................................................... 116
xvii
LIST OF ABBREVIATIONS
2-MeTHF
B3LYP
o
C
CCnap
CV
d
DFT
DMSO
Dnpebpy
Dppe
DPV
ESI
ESMV
fs
HOMO
IC
i
Pr
ISC
Kc
L
LMCT
LUMO
M
M2
MALDI-TOF
Me
mL
mV
MLCT
m/z
n
Bu
nm
NMR
OAc
Py

s
S
2-Methyltetrahydrofuran
Brecke-3 parameter Lee-Yang-Parr
Degrees Celsius
1-ethynylnaphthalene
Cyclic Voltammetry
doublet
Density Functional Theory
Dimethyl Sulfoxide
4,4'-dineopentylester-2,2'-bipyridine
Diphenylphosphinoethane
Differential Pulse Voltammetry
Electrospray Ionization
Excited State Mixed Valence
Femtosecond
Highest Occupied Molecular Orbital
Internal Conversion
Isopropyl
Intersystem Crossing
Comproportionation constant
Ligand
Ligand-to-Metal Charge Transfer
Lowest Unoccupied Molecular Orbital
Moles per liter
Dimetal unit
Matrix Assisted Laser desorption Ionization Time of Flight
Methyl
Milliters
Millivolts
Metal-to-Ligand Charge Transfer
Mass to charge ratio
Normal butyl
Nanometers
Nuclear Magnetic Resonance
Acetate
Pyridine
pi-orbital
Singlet; seconds
Electronic State
xviii
SDD
TA
TD-DFT
THF
TiPB
Th
UV
vis
Stuttgart/Dresden
Transient Absorption
Time-Dependent Density Functional Theory
Tetrahydrofuran
2,4,6-triisopropylbenzoate
Thienyl
Ultraviolet
Visible
xix
CHAPTER 1
INTRODUCTION
1.1
Introduction
Growing concerns over meeting the world’s energy needs in sustainable ways has
led to an increased interest in energy-reducing and energy-harvesting technologies, such
as light emitting diodes (LEDs) and photovoltaics (PVs).1 Currently, inorganic
semiconductors dominate the photovoltaic market, however, due to the high material and
processing costs of these devices, solar electricity cannot compete effectively with
electricity from fossil fuels.2,3 Organic solar cells are an interesting alternative to the
traditional inorganic semiconductors in that they can be fabricated more easily from less
expensive materials and can be made flexible and light weight. Integrating metal atoms
into conjugated organics to form metallo-organic hybrid light harvesters offers the
advantages of providing greater tunability of the band gap as well as increasing the ability
to form a long-lived triplet excited state.2 This research focuses on the photophysical
properties of metallo-organic hybrid complexes where the core is a multiply bonded
dimetal unit with the goal of understanding the photophysical properties and excited state
character, both of which are important for effective application in optoelectronic devices.
1.2
Multiple Bonds Between Metal Atoms
Not until 1963 was it discovered that multiple bonds could exist between metal
atoms, at which time it was determined that a double bond existed between rhenium
atoms specifically in the cluster complex [Re3Cl12]3-.4-6
It is interesting that after this
discovery some scientists thought that the only remaining work to be done in the area of
ReIII chemistry was to work out an aqueous synthetic route to attain the [Re3Cl12]3- cluster
from the readily available [ReO4]-.
However during the quest to find this synthetic
method, a much more interesting complex was made containing the [Re2Cl8]2- ion.7,8 It
was via this [Re2Cl8]2- ion where the counter cation was potassium or pyridinium, that it
was first discovered that quadruple bonds could exist between metal atoms.7-9 This
realization was in part made possible by the technology of x-ray crystal diffraction and
the insight it lent to molecular structures, since elemental analysis alone would have
indicated the mononuclear [ReCl4]-.9 During the determination of the crystal structure of
K2Re2Cl8·2H2O, two important details were discovered. First, that the distance between
a pair of rhenium atoms was unusually short (2.22 Å), shorter even than the distance
between atoms in rhenium metal (2.75 Å); secondly, the eight chloride ligands
coordinating to the two rhenium atoms were aligned in an eclipsed geometry whereas,
due to repulsion between the chloride atoms, a staggered geometry was expected (Figure
1.1). 9,10
2
Figure 1.1 Image of the structure of [Re2Cl8]2- ion in K2Re2Cl8•2H2O. Reproduced from
reference 7.
Once it was realized there must be some force encouraging this short bond
distance and eclipsed geometry, F. A. Cotton and co-workers proposed the interactions
between the d orbitals on each of the rhenium atoms in the manner shown in Figure 1.2
that we now understand to be the interactions that occur to form the quadruple bond
between transition metal atoms.10,11 The bonding is explained by the overlap of the dz2
orbital of one metal with that orbital of the second metal atom to form a bond, the dyz
and dxz orbitals of each metal interacting to form twobonds, and the dxy orbitals
interacting to form a  bond.
3
Figure 1.2 Interactions between d orbitals during formation of the quadruple bond.
Reproduced from reference 12.
This description of bonding between metal atoms opened the door to an entirely
new field of chemistry involving multiply bonded metal complexes. Prior to 1964 a few
quadruply bonded metal complexes had been synthesized, however their identity was not
understood until the quadruple bond was discovered in K2Re2Cl8·2H2O. After this
breakthrough many singly and multiply bonded metal complexes (bond order 2-4) were
synthesized, which led to the preparation of bimetallic systems with almost all of the first
three rows of transition metals in group 5 through group 10, with the exception of
manganese and tantalum.9
4
1.3
Paddlewheel Complexes
A subgroup of multiply bonded metal complexes, called paddlewheel complexes,
having the structure shown in Figure 1.3 are made up of a dimetal unit with chelating
ligands bridging the metals. The chelating ligands can be attached to the metal centers
via N, O, P, or S atoms and nonchelating ligands or solvent may or may not coordinate
axially depending on factors that include the oxidation state of the metal and the steric
bulk of the chelating ligands.13,14
Figure 1.3 The basic structure of a paddlewheel complex. Reproduced from reference 13.
The synthesis of molybdenum paddlewheel complexes with carboxylate bridging
ligands is straightforward. Air stable Mo(CO)6 is refluxed at 140 oC under an inert gas in
a 1:2 ratio with a carboxylic acid to produce Mo2(O2CR)4, where R is an alkyl or aryl
group.15 The preparation of the tungsten analog is slightly more complicated but in most
cases the complexes W2(O2CR)4 can be synthesized by reducing WCl4 via a sodium
amalgam in the presence of the sodium salt of a carboxylic acid in THF. 16,17 Dirhenium
5
tetracarboxylates with axially bound halides, such as Re2(O2CCH3)4Cl2, can be
synthesized by refluxing [Bu4N]2Re2Cl8 with acetic acid and acetic anhydride until the
product precipitates out of solution.18 Carboxylate bridging ligands are fairly labile and
in the case of the molybdenum and tungsten complexes are easily exchanged with other
carboxylate ligands by stirring at room temperature in toluene to generate heteroleptic
paddlewheel complexes. If the ligands on the homoleptic starting material are sterically
bulky, such as in 2,4,6-triisopropylbenzoate, and 2 equivalents of the desired ligand are
added, substitution results in the formation of the trans product referred to as the bis-bis
complex (Figure 1.4a). In the case of Re2(O2CR)4Cl2 complexes, the M26+ core can be
converted to a complex with a M24+ core by refluxing the dimetal tetracarboxylate in
methanol with neutral chelating phosphine ligands which replace two carboxylate ligands
on the molecule (Figure 1.4b). At this point the carboxylate ligands can be exchanged on
the ReII complex by further refluxing in methanol with greater than 2 equivalents of
ligand. 19
6
(a)
(b)
Figure 1.4 (a) Synthetic route to bis-bis heteroleptic dimetal complexes, where M = Mo,
and W, R = 2,4,6-triisopropylbenzoate. (b) Synthetic route to cis heteroleptic dirhenium
paddlewheel complex with carboxylate and dppm ligands, where R = methyl and dppm =
bis(diphenylphosphino)methane. Modified from reference 19 and 20.
1.4
Absorption of Light by Molecules
Since this work focuses on exploring the photophysical properties of multiply
bonded metal complexes it is important to understand some basic photophysical concepts.
Chemical species can exist only in discrete energy states, and when a molecule is in its
most stable state it is said to be in the ground state. A molecule can interact with light,
thus gaining energy and producing an excited state. Depending on the wavelength of
incident radiation, the molecule can be excited rotationally, vibrationally, or
electronically. The absorption of lower energy radiation (infra-red) typically leads to
rotationally and vibrationally excited species, while absorption of higher energy radiation
(ultra-violet/visible) leads to electronically excited species.21
7
When considering a
radiative electronic transition within a molecule, the molecule can be thought of as an
electric dipole and absorption of electromagnetic radiation causes an electric dipole
transition to occur. The transition dipole moment (D) for an electronic transition from
the ground state to an excited state is defined by equation 1.1 where M represents the
dipole moment operator connecting states a and Ψb.
D = <a|M|Ψb>
(1.1)
The transition dipole moment will exist if the direct product of the ground and excited
state wavefunctions with the dipole moment operator contains the totally symmetric
representation, and it will be zero if this is not true. The dipole moment operator is odd
with respect to inversion, therefore it must connect an odd and even wavefunction for the
results to be non-zero. This leads to the selection rule, Laporte’s Rule, which states that
transitions between states of the same symmetry (symmetric/even (g) or asymmetric/odd
(u) with respect to an inversion center) are forbidden.22
The wavefunction of a state, Ψa, can be separated into the nuclear component
(Ψan), the electronic component (Ψao), and the electron spin component (Ψas).23
Ψa = Ψan · Ψao · Ψas
(1.2)
The allowedness of a transition depends on the overlap between the ground and excited
state wavefunctions. The Frank-Condon principle states that electronic motion is much
faster than nuclear motion, therefore electronic transitions will occur most favorably
between states that have similar nuclear structures.
Transitions will also be most
favorable between states with large orbital overlap. Finally, the spin component of the
ground and excited state must be taken into consideration. The dipole moment operator
does not couple electronic spin, therefore, the transition dipole moment will be zero
8
unless the spin of the ground and excited states are the same. This leads to the selection
rule which states that transitions between states of different multiplicities are spin
forbidden.22
Experimentally, the absorption of light by a molecule and its transition from an
electronic ground state to an electronic excited state is observed by UV-Vis absorption
spectroscopy. This produces a spectrum of absorption bands at frequencies specific to
the spacing of energy levels in the molecule under investigation.21
The larger the
transition dipole moment (D) is, the more “allowed” the transition and the more intense
the absorption band will be. The intensity of an electronic transition, can be measured by
its oscillator strength, f, which can be estimated from the experimental absorption
spectrum according to following equation:
f ~ max 
(1.3)
where is the extinction coefficient and  represents the area under the absorbance
curve.23
As previously mentioned, chemical species exist in discreet or quantized energy
levels. Each electronic state has more closely spaced vibrational and rotational levels
associated with it. Upon absorption of a photon it is possible for an electron to be
promoted from the ground state’s lowest energy vibrational level ( = 0) of the molecule
to various vibrational levels within the electronic excited state (′ = 0, 1, 2, 3, etc.).
These absorptions to various vibrational levels are sometimes observed within an
electronic absorption band (See Figure 1.5). The spacing between these vibronic features
indicates the spacing between the vibrational levels in the excited state and can indicate
9
the dominant type of vibration occurring in the excited state, giving insight into the
structural features of the latter.
Absorption
Emission
Absorption
Emission
Figure 1.5 Left: Representation of molecule with distinct vibrational substates. Right:
Absorption and emission spectra with vibrational structures. Reproduced from ref 23.
1.5
Excited State Decay Pathways
It is known from organic compounds that when a molecule initially absorbs light
and is placed in an excited state, it relaxes very quickly and non-radiatively to the lowest
energy excited state of the same spin (S1) by internal conversion (IC) (Figure 1.6). S1
further relaxes to the grounds state (S0) via any of the following pathways shown in
Figure 1.6: (a) nonradiatively (giving off energy as heat) decays to S0 (b) radiatively
decays – emitting light (c) intersystem crosses (ISC) to a lower lying excited state with a
different spin (T1), followed by radiative or nonradiative decay to the ground state from
this T1 state. Alternately, rather than returning to the ground state, an excited organic
compound may use the excess energy to undergo a chemical reaction.
Emission from an excited state with the same spin as the ground state is called
fluorescence and emission that results from an excited state with a different spin is called
10
phosphorescence (Figure 1.6).23,22
Excited states in inorganic systems can be more
complex and unique than those of organic molecules due to high symmetry, resulting in
degenerate molecular orbitals and open-shell ground state configurations (i.e. partially
filled highest occupied molecular obitals, HOMOs). These properties can lead to states
with spin multiplicities other than singlets and triplets, excited states with the same
electronic configuration as the ground state, and multiple states with different
multiplicities and a single electron configuration.24 While excited state deactivation is
well understood in organic molecules, inorganic systems are more complex and do not
always follow the same trends; for example the Jablonski diagram of a CrIII complex,
Cr(acac)3, is shown in Figure 1.7. It can be seen that when the complex is excited into a
higher 4LMCT state, rather than first relaxing non-radiatively to the lowest energy
excited state of the same spin, as would be anticipated based on what is known about the
photophysics of organic complexes, ISC occurs on a faster timescale and the 2E state is
populated directly from the 4MLCT.24,25
11
Sn
*

Internal Conversion (IC)
S1
Intersystem crossing (ISC)
T1
Nonradiative decay (ISC)
Phosphorescence
Nonradiative decay (IC)
Fluorescence
S0
Absorption
*

*

Figure 1.6 Simplified state energy diagram displaying transition pathways between
states. Modified from reference 23.
12
Figure 1.7 Jablonski diagram of [Cr(acac)3]. Reproduced from reference 24.
The energy and intensity of the luminescence and excited state kinetics of a
complex can be detected using steady-state emission spectroscopy and time-resolved
spectroscopy, respectively, including emission decay or transient absorption. Emisson
spectra can also contain vibronic features, where relaxation takes place from the lowest
vibrational level of the excited state (′ = 0) to a range of vibrational levels in the ground
state ( = 0, 1, 2, 3, etc.) (Figure 1.5).
Transient absorption is a pump-probe technique whose time resolution typically
depends on the length of the pump laser pulse, which elevates a portion of the population
from the ground state into the excited state. Once the excited state is populated, a probe
light is then used to measure the absorption profile of the excited species. In practice this
13
allows the study of the absorption profiles of S1 and T1.
Monitoring changes in
absorption as a function of time can be used to determine the rates of deactivation of the
excited state, formation of other states or photochemical products, and recovery of the
ground state. Lifetimes observed for the deactivation of excited states are the inverse of
the sum of the rates of all the deactivation pathways. Examples based on Figure 1.6 are
given by eq. 1.4 for the lifetimes of S1 (S) and T1 (T), where kr is the rate of
fluorescence, knr is the rate of internal conversion from S1 to S0, and kISC is the rate of
intersystem crossing from S1 to T1, kTr is the rate of phosphorescence, and kTISC is the rate
of intersystem crossing from T1 to S0 23:
S = 1 / (kr + knr + kISC)
and
T = 1 / (kTr + kTISC )
(1.4)
In general, allowed transitions have greater rate constants than those that are forbidden.22
1.6
Breakdown of Selection Rules
Selection rules provide a framework for the prediction of which transitions may or
may not be observed experimentally. However, forbidden excited state deactivation
pathways, such as intersystem crossing and phosphorescence, are typically observed.
These transitions are forbidden when states are classified by a single electronic orbital
configuration or a single spin configuration. However, state mixing can occur, such that
a state can no longer be classified solely in terms of just one electronic orbital
configuration or spin type. One way that state mixing occurs is via spin-orbit coupling,
which is the interaction between an electron’s spin magnetic moment and the electron’s
orbital motion magnetic moment.
An accelerating charged particle can produce a
14
magnetic field according to equation 1.5, where He is the magnetic field, E is the electric
field of the electron, is the velocity of the electron.
He = E ∙  / c
(1.5)
An electron moves around the nucleus in its orbital producing a magnetic field and
thereby has an orbital motion magnetic moment; the electron spins around its own axis
creating a magnetic field and has a spin magnetic moment. The magnetic field produced
by the electron’s orbital motion (He) now has the capability to act as a momentof force,
or torque, on the electron’s spin magnetic moments), causing it to flip. The overall
angular momentum of the electron is conserved during the spin flip by compensating
with an orbital jump (Figure 1.8).23 Since spin-orbit coupling increases with atomic
number, it is an important effect to consider when analyzing the photophysical properties
of complexes containing second and third row transition metal atoms.
Figure 1.8 Representation of spin-orbit coupling in terms of a physical orbital.
Reproduced from reference 23.
15
1.7
Absorption of Quadruply Bonded Metal Complexes
As F. A. Cotton points out in Multiple Bond Between Metal Atoms, the electronic
absorption spectra of M2n+ complexes include many types of transitions but significant
attention has been given to those involving the  and * orbitals, which depending on the
number of electrons in the ground state, can fall into one of the following categories: (1)
2 → * (2) → * or (3) 2* → *2.9 Based on calculations of M2Cl8n- quadruply
bonded metal complexes where M = Mo2+, W2+ and Re3+, the lowest energy transition is
from the  orbital to the * orbital.26
The  → * electronic transition is dipole allowed, however, it is relatively weak
due to the fact that there is limited overlap between the dxy orbitals forming the  bond
and the square of orbital overlap is proportional to the intensity of the transitions
involving these orbitals.9,27 Though weak, the  → * electronic transition has been
observed now in many dimetal complexes,9,28,29 a few of which will be a focus of this
discussion to enable a general foundation of their photophysical properties to be built
(also see Table 1.1).
Homoleptic molybdenum complexes [Mo2(L)8]4- (L = Cl-, CH3-,
NCS-) and [Mo2(L)8]4+ (L = NH3, CH3CN, H2O) represent a few of the complexes that
have been investigated. The  → * transition in heteroleptic Mo2Cl4(PR3)4 complexes
and complexes with bridging ligands such as mhp (2-hydroxy-6-methylpyridine anion)
have also been studied. The  → * transitions of these complexes range from 475 to
690 nm.9,28,29
Fewer ditungsten complexes have been synthesized and studied
spectroscopically, however a fair number of systems exhibiting a singlet →*
absorption as the lowest energy transition have been observed, including the octachloride
16
and octamethyl ions.
Some heteroleptic W2 complexes with four halogen or alkynyl
ligands and four phosphine ligands, as well as the tetra(mhp) complex exhibit →*
with maxima that range from 570 to 775 nm.9,28,29 And finally,  → * transitions
ranging from 540 to 1000 nm have been observed in Re2L82- complexes where L = F-, Cl-,
Br-, I-, NCS-, or CH3-.9,28,29
One ligand type that has thus far been left unmentioned is the carboxylate
bridging ligand. Due to its low lying* orbitals, a very intense metal-to-ligand charge
transfer (MLCT) transition is typically observed in these complexes. In the cases where
the conjugation of an R group attached to the CO2- is minimal or nonexistent and the
delta based HOMO orbital is low in energy as is the case in molybdenum complexes, the
 → * transition remains the lowest energy transition; however, the higher energy side
of the  → * band may overlap and be partly obscured by the MLCT band. As the
conjugation with the R group is increased, the* orbital of the ligand becomes so low in
energy that it falls below the * orbital; in this case the lowest energy transition is MLCT
in nature and the  → * transition is completely buried under the intense MLCT
peak.16,30 On going from molybdenum to tungsten, the metal-based HOMO is raised to
higher energy resulting in a shift of the MLCT band to lower energy and again
completely obscuring the  → * transition.31 Despite these complications, the  → *
transition has been clearly observed in a few tetracarboxylate complexes namely,
Mo2(O2CH)4, Mo2(O2CMe)4, Mo2(O2CMe3)4, Mo2(O2CCF3)4, K4Mo2(O2CCH2NH3)4 with
max ~ 440 nm, W2(O2CMe3)4 with max ~ 470 nm, and Re2(O2CCMe3)4Cl2 with max ~
500 nm.32-35
17
The assignment of the  → * absorption band in quadruply bonded complexes
was confirmed by the observation of a vibronic progression whose energy matched the
totally symmetric stretch of the M-M bond. The frequencies of these bands are similar to
the ground state stretching frequencies, however since the bond order in the excited state
is 3.5 rather than 4.0, the frequencies are shifted to lower energies by ~ 30 cm-1.9
Table 1.1 Quadruply bonded M2 complexes exhibiting* transitions.
Complex
1(*)
1(*)
Absorption
nm
Emission
nm ()
Mo24+
W24+
Re26+
Mo24+
M2Cl8n-
525a
600a
690b
670 j
(205 ps) l
M2(CH3)8n-
510c
595d
540c
M2Cl4(PMe3)4
585e
660e
M2Cl4(PnBu3)4
585f
M2(mhp)4
505g
570g
M2(O2C(CH3)3)4Cl0-2
440h
470h
W24+
Re26+
790 k
(75 ns)
670m
(140 ns)
665n*
(16 ns)
a
495i
Ref. 9. b Methanol, ref. 36. c Diethyl ether, ref. 37. d 2-methyltetrahydrofuran, 77K, ref.
38. e 2-methylpentane, ref. 39. f 2-methylpentane ref. 40. g Tetrahydrofuran, ref. 29
h
CH2Cl2, ref. 41. i Sample in solid state, ref. 34. j Sample in solid state, ref. 42. k CH2Cl2,
ref. 40. l 2M HCl, room temp., ref. 43. m 2-methylpentane, room temp., ref. 44. n 2methylpentane, room. temp., ref. 40. * note that a longer live excited state has also
observed in this complex in CH2Cl2 but the shorter lifetime matches the luminescence
decay and is attributed to the 1* state (ref. 43).
18
1.8
Emission of Quadruply Bonded Metal Complexes
Emission from the 1* state is easily observed in Mo2Cl4(PnBu3)4, where
excitation into the * absorption band produces luminescence that is a mirror image of
the absorption, with overlap at the  = 0 → ′ = 0 transition. In this complex the ligands
force the excited state to remain in the same geometry as the ground state, resulting in the
mirror image in the absorption and emission. Emission from the 1* state has also been
observed in Mo2Cl84- and Re2Cl82-. However, it is thought that once in the excited state
these molecules twist from the ground state D4h geometry to D4d, such that in solution the
emission arises from the 1* state with D4d geometry and only in the solid state is
emission from the excited state with D4h symmetry observed. The emission maxima and
excited states lifetimes of these emissive complexes are listed in Table 1.1.
Luminescence from the 3* of a quadruply bonded dimetal complex was finally
observed in 2003 in Re2Cl2(p-OCH3form)4, where p-OCH3form = N, N’-di(panisyl)formamidinate. Emission from this excited state was not previously detected
because it was predicted that the 3* state was so low in energy that the relaxation to the
ground state would be very weakly emissive or completely nonradiative. The uniqueness
of the Re2Cl2(p-OCH3form)4 complex is that the formamidinate ligands, with their
nitrogen linker atoms, have  orbital combinations which can mix with the  and *
orbitals. The strongest of these M-L interactions is between the * and the b1u (middle
ligand nonbonding orbital) due to good overlap and energy match; therefore this
interaction has the most significant effect on the energies of the metal based orbitals. The
b1u orbital donates electron density into the * orbital, increasing its energy along with
19
the 1* and 3* states as seen in Figure 1.10, allowing the 3* emission to be observed
in the visible region. 45-47 The Re2Cl2(p-OCH3form)4 emission was observed at 825 nm in
MeCN with strong vibronic features at 77K with  = 259 cm-1, similar to the ground
state (ReRe) of 275-295 cm-1, and the triplet excited state has a lifetime of 1.4 s in
CH2Cl2. 45
Figure 1.9 Diagram depicting orbital interactions between formamidinate ligand 
orbitals and metal-metal orbitals. Reproduced from reference 47.
The 3* emission has now also been observed in dimetal tetracarboxylates where
the M = Mo2, MoW, and W2 (see Figure 1.11). The 3* emission of Mo2(TiPB)4, where
TiPB = triisopropylbenzoic acid, has a maxima at ~ 1100 nm and as the tungsten metal
20
content is increased in these complexes the peak shifts to shorter wavelengths: 980 nm
for MoW and 815 nm for W2. The emission spectra exhibit vibronic progressions  =
300-450 cm-1, and the triplet excited state lifetimes for these complexes in THF are 43,
27, and 1.3 s for Mo2, MoW, and W2 respectively.16 Emission from the 3* state was
thought to have been seen previously in Mo2(O2CCF3)4, however it is now understood in
light of the M2(TiPB)4 complexes that this was really emission from the 1*.16,48 The
long-lived 3* state was first recorded by ns-TA in 2005 in a set of dimolybdenum and
ditungsten tetracarboxylates, where it was attributed to a 3MLCT state.
In these
complexes the emission was monitored at < 800 nm and only a single emissive excited
state was apparent: the 1MLCT state.
The emissive 1MLCT excited state in these
complexes has a short lifetime (ps) and the longer lived excited state (s), at least in the
molybdenum complexes, can now be assigned as the 3* based on the emission and
lifetimes measured for similar dimolybdenum tetracarboxylate complexes.16,49,50
21
Figure 1.10 Absorption (THF, r.t.) and near-IR emission spectra (2-MeTHF, 77K) of
M2(TiPB)4 complexes. Mo2 (red), MoW (blue), W2 (green). Reproduced from reference
16.
It seems that in most dimolybdenum tetracarboxylate complexes investigated to
date, with the exception of Mo2(TiPB)2(6-carboethoxy-2-azulenecarboxylate)2, that the
lowest energy excited state is an emissive 3* state.16,51,52,20 However, in W2(O2CR)4
compounds the photophysical properties are slightly more complex.
In W2(O2CR)4
complexes with less conjugated ligands having higher energy * orbitals such as R = tBu
or TiPB, the lowest energy excited state is attributed to a 3* state which emits with
maxima at 815 nm.16 However, when a more conjugated ligand with lower energy *
orbitals
is
used
such
as
the
2,2’:5’,2”-terthiophene-5-carboxylate
in
W2(TiPB)2(2,2’:5’,2”-terthiophene-5-carboxylate)2, the lowest energy excited state
22
becomes non-emissive and has a much shorter lifetime (ns v. s) compared to W2(TiPB)4.
In the case of W2(TiPB)2(2,2’:5’,2”-terthiophene-5-carboxylate)2 it is predicted that the
lowest energy excited state is 3MLCT in nature.16,20
1.9
Statement of Purpose
The purpose of this dissertation is to study the photophysical properties of
complexes containing multiply bonded dimetal units at their core.
This research
encompasses a range of metals, bond orders, and ligands, resulting in a diverse group of
systems which allow for comparison of the different photophysical properties that arise as
each of the various components are altered.
Chapter 2 explores rhenium dimetal complexes where the bond order between the
metal atoms ranges from three in Re24+ complexes to four in Re26+ complexes. The
effects of changing the metal core from a 242*2 to 242 are explored.
A
comparison is also made between the photophysical properties of Re2(O2CC6H4NO2)4Cl2,
which emits from a 3* excited state, with other analogous dimolybdenum and
ditungsten tetracarboxylates and dirhenium dichloro tetraformamidinates, which also
emit from 3* states.
Chapter 3 deals with dimetal tetracarboxylate complexes where the carboxylate
ligands are composed of the thiophene unit linked to the carboxylate tether via a vinyl or
ethynyl moiety. Varying the linker unit from a double to a triple bond allows for
comparison of the electronic delocalization through the metal centers in the complexes.
Chapter 4 focuses on understanding the photophysical properties of quadruply
bonded M2(O2CR)4 complexes where M = Mo, W and R = tolylethynyl, and
anthrylethynyl. The nature of the photoexcited state in these complexes is explored and a
23
comparison is made with similar types of complexes lacking the ligand C≡C triple bond
linking unit.
24
CHAPTER 2
2. PHOTOPHYSICAL PROPERTIES OF Re24+ AND Re26+ CARBOXYLATE
COMPOUNDS
2.1
Introduction
In dye-sensitized solar cells it has been determined that efficient charge injection
from a dye's singlet or triplet excited state53,54 is in part dependent on strong coupling
between the titanium surface ions and the moiety of the dye on which the excited electron
is localized.55 This coupling is achieved by forming a coordinative bond between the dye
and the titanium ions,55 which in Ru2+ complexes are often formed via a pendant
carboxylate moiety on the aromatic ligand.
In quadruply bonded tetracarboxylate
complexes a similar coordination modality could be achieved by introducing a second
carboxylate group onto the aromatic ligands available for bonding to the surface.55 This
understanding of charge injection efficiency led us to investigate multiply bonded
complexes with excited states that are metal-to-ligand charge transfer (MLCT) in nature.
Quadruply bonded M2(O2CR)4 and M2(TiPB)2(O2CR)2 complexes, where M = Mo, and
W, have a ground state electron configuration of 242. It has been shown that exciting
these types of complexes into their lowest energy absorption band populates a 1MLCT
excited state at which point fairly rapid intersystem crossing ((ISC)
≈
ps) to a longer
lived triplet excited state occurs.50,49 In the case where M = Mo, this ISC leads to
population of an emissive 3* state16 (
≈
s) whose maximum is ligand and solvent
25
independent52 and exhibits a vibronic progression20  ~ 390 cm-1 that is similar in
energy to the ground state (MoMo) of 397-406 cm-1 for Mo2(O2CR)4 where R = CH3,
and CF3.56,57,48 When M = W, the lowest energy triplet state can be 3* or 3MLCT in
nature depending on the ligation sphere.16,20
While quadruply bonded ditungsten
tetracarboxylates do exist having both singlet and triplet MLCT excited states, their
extreme sensitivity to oxidation,16 leading to decomposition, may make device
manufacturing more difficult and device stability less reliable. With this knowledge in
hand, we wanted to explore other multiply bonded complexes in hopes of finding a stable
complex that possessed singlet and triplet MLCT states suitable for photovoltaic
applications such as dye-sensitized solar cells. We were naturally curious about the
excited state character of related multiply bonded carboxylates of rhenium. Rhenium
forms an extensive series of quadruply bonded complexes, MM 242, with the Re26+
core, as well as the triply bonded complexes with Re24+ core, MM 2422. In order to
observe intense
1
MLCT transitions a good -acceptor carboxylate ligand, p-
nitrobenzoate, was selected. Described here are studies of the photophysical properties of
this ligand attached to the Re24+ and Re26+ cores.
2.2
Synthesis
Re2(dppm)2(O2CC6H4-p-NO2)2Cl2 was prepared by the reaction between the
known compound Re2(dppm)2(O2CCH3)2Cl2 reported by Walton et al. and p-nitrobenzoic
acid (>2 equiv.) in refluxing methanol.19 The compound is very sparingly soluble in
methanol but more soluble in THF and dichloromethane from which it can be crystallized
yielding dark red-brown needle shaped crystals.
26
Re2(O2CC6H4-p-NO2)4Cl2 was prepared by the carboxylate exchange reaction
involving Re2(O2CCH3)4Cl2 and p-nitrobenzoic acid in methanol. This led to a mixture
of carboxylates Re2(O2CCH3)4-x-(O2CC6H4-p-NO2)xCl2 as determined by MALDI-TOF
MS. Employing reactions in o-dichlorobenzene and an excess of p-nitrobenzoic acid the
compound Re2(O2CC6H4-p-NO2)4Cl2 was obtained although trace quantities of the
complex Re2(O2CCH3)(O2CC6H4-p-NO2)3Cl2 were present as indicated by MALDI-TOF
MS. This impurity does not invalidate the conclusions that are pertinent to the theme of
this work. Re2(O2CC6H4NO2)4Cl2 is a tan colored solid which is very sparingly soluble
in dichloromethane, THF, and DMSO.
2.3
Molecular and Single Crystal Structure of cis-Re2(dppm)2(O2CC6H4-pNO2)2Cl2.
A summary of crystallographic data is given in Table 2.1 and selected bond
distances are given in Table 2.2 (full details given in Appendix A). An ORTEP drawing
of the molecule is given in Figure 2.1 where it can be seen that the two Cl ligands lie
along the Re-Re axis and the two dppm and carboxylate ligands are mutually cis. The
Re-Re distance of 2.320(8)Å is similar to that of the related acetate complex, 2.315(1)Å,
reported earlier by Walton et al. and is expected for a ReRe triple bond of molecular
orbital configuration 2422.20 The ReRe distance in Re2(O2CCH3)4Cl2 is 2.2240(5)Å
for further comparison.9,58 The other Re-ligand atom bond distances are comparable to
those in the Walton structure. As can be seen in Figure 2.1, the central paddlewheel unit
is not eclipsed and O-Re-Re-O torsion angle is 14.5(3)o. Of some significance in viewing
this structure is the near co-planarity of the O2C-C6H4-p-NO2 groups. This type of co-
27
planarity is typical of that in Mo24+ and W24+ carboxylates that show extended M2 to
ligand  interactions.
Figure 2.1 ORTEP drawing of Re2(dppm)2(O2CC6H4NO2)2Cl2 drawn with 50%
probability ellipsoids. Hydrogen atoms are omitted for clarity. The solvent molecule of
THF is shown here. The Re complex contains a crystallographic two-fold rotation axis.
28
Table 2.1 Crystallographic data for Re2(dppm)2(O2CC6H4NO2)2Cl2 · 2 THF.
.
Molecular formula
C64 H52 Cl2 N2 O8 P4 Re2 + 2(THF)
Formula weight
1688.46
Temperature
150(2) K
Wavelength
0.77490 Å
Crystal system
Monoclinic
Space group
C2/c
Unit cell dimensions
a = 31.062(7) Å, b = 10.454(3) Å, c = 24.183(6)
Å
b= 124.225(3)°
Volume
6493(3) Å3
Z
4
Density (calculated)
1.727 Mg/m3
Absorption coefficient
4.769 mm-1
F(000)
3352
Crystal size
0.08 x 0.03 x 0.01 mm3
Theta range for data
collection
3.97 to 29.12°
Index ranges
-38<=h<=38, -13<=k<=13, -30<=l<=30
Reflections collected
34819
Independent reflections
6692 [R(int) = 0.131]
Completeness to theta =
29.12°
99.5 %
Refinement method
Full-matrix least-squares on F2
Data / restraints /
parameters
6692 / 0 / 415
Goodness-of-fit on F2
0.971
Final R indices
[I>2sigma(I)]
R1 = 0.0500, wR2 = 0.1002
R indices (all data)
R1 = 0.1040, wR2 = 0.1197
Largest diff. peak and
hole
1.512 and -2.242 e/Å3
29
Table 2.2 Select bond distances for Re2(dppm)2(O2CC6H4NO2)2Cl2.*
2.4
Electronic Absorption Spectra
The electronic absorption spectrum of the triply bonded Re24+ complex,
Re2(dppm)2(O2CC6H4NO2)2Cl2, in dichloromethane is shown in Figure 2.2 and that of the
quadruply bonded Re26+ complex, Re2(O2CC6H4NO2)4Cl2, in THF is shown in Figure
2.3. In Figure 2.2 we see that the most intense absorption in the visible region of the
spectrum arise from a broad band at max ~ 370 nm,  ~ 10,000 M-1cm-1, that tails to
longer wavelengths. However, there is a weaker absorption at lower energy, max ~ 790
nm, with ~ 200 M-1cm-1 (shown in inset). The parentage of this and other absorption
features are discussed below. The energy and intensity of the absorption bands measured
for Re2(dppm)2(O2CC6H4NO2)2Cl2 in CH2Cl2 are very similar in appearance to those of
the previously published Re2(dppm)2(O2CCH3)2Cl2.19
The absorption spectrum of Re2(O2CC6H4-p-NO2)4Cl2 shown in Figure 2.3
reveals that the absorption at ~350 nm, which tails into the visible region, gives rise to its
30
tan color. Because of its low solubility any weaker bands at lower energies were not
observed, however, their presence cannot be ruled out.
It is evident from Figures 2.2 and 2.3 that neither of these complexes bearing the
potentially -accepting p-nitrobenzoate ligands have intense absorption in the visible
region that may be characterized as MLCT in nature. This observation is in sharp
contrast to related molybdenum and tungsten, M24+, containing complexes. For example,
Mo2(O2CC6H4-p-NO2)4 exhibits an intense absorption at max ~ 534 nm,  ~ 13,700 M1
cm-1 assignable to the 1MLCT to the p-nitrobenzoate ligands.59
Figure 2.2 Absorption spectrum of Re2(dppm)2(O2CC6H4NO2)2Cl2 in CH2Cl2. Inset:
Magnified view of absorption spectrum in region 450 – 1000 nm.
31
1.4
Absorbance / a.u.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
700
800
900
Wavelength / nm
Figure 2.3 Absorption spectrum of Re2(O2CC6H4NO2)4Cl2 in THF.
2.5
Electronic Structure Calculations
In order to assist in the interpretation of the electronic absorption spectra of these
two complexes we have carried out electronic structure calculations employing density
functional theory with the aid of the Gaussian03 suite of programs, and to reduce
computational time we have modeled the dppm ligands as H2PCH2PH2.
The frontier orbitals of the model compounds cis-Re2(H2PCH2PH2)2(O2CR)2Cl2
(R = Me, p-C6H5-NO2) are shown in Figure 2.4, where we compare the acetate with the
p-nitrobenzoate complexes. We make this comparison because we would not expect the
acetate complex to possess an intense 1MLCT absorption. In both cases the HOMO is the
32
Re2 * orbital with some mixing due to the filled non-bonding CO2  orbitals. The
calculated energy of the HOMO for the acetate and p-nitrobenzoate complexes are -5.30
eV and -5.69 eV respectively. The difference of nearly 0.4 eV reflects the greater
electronic withdrawing properties of the p-nitrobenzoate. In both complexes the HOMO
is the Re2 *, while the HOMO-1 is Re2  and Re-Cl*, the HOMO-2 and HOMO-3 are
Re2 and Re-Cl *, and the HOMO-4 is the Re2 . The nearly isoenergetic LUMO and
LUMO+1 for the acetate complex are Re2 * orbitals with some Cl p -antibonding
character. For the p-nitrobenzoate compound the LUMO and LUMO+1 are also of
similar energy with respect to each other but notably lower in energy compared to the
acetate complex. The HOMO-LUMO gap for cis-Re2(H2PCH2PH2)2(O2CCH3)2Cl2 is
2.91 eV and that for the p-nitrobenzoate complex is 2.85 eV. However, the major
difference between the two complexes is that the LUMO and LUMO+1 for the pnitrobenzoate complex have considerable ligand * character in addition to the Re2 *.
33
Re2(dppm)2(O2CCH3)2Cl2
Re2(dppm)2(O2CC6H4NO2)2Cl2
-1
Energy (eV)
-2
-3
-4
-5
-6
-7
Re2 , Cl p *
Re2 , Cl p *
Re2 , Cl p *
Re2 , Cl p *
Re2 , Cl p
Re2 , Cl p *
Re2 , Cl p *
Re2 , Cl p
Figure 2.4 Energy diagram of frontier orbitals of Re2(dppm)2(O2CR)2Cl2 (isovalue =
0.03).
In order to further aid in the interpretation of the spectroscopic properties of the
Re24+ p-nitrobenzoate complex we carried out time dependent DFT calculations. These
calculations predict that the lowest energy transition is a result of the movement of an
electron from the HOMO to combinations of LUMO, LUMO+1, LUMO+2, and for the
higher energy band at 745 nm from the HOMO to the same unoccupied orbitals with the
addition of LUMO+3. These are a mixture of MM and MLCT transitions and perhaps
most importantly have very low oscillator strengths, f = 0.0004 and 0.0006 (See Figure
2.5-2.6 and Table 2.3). The most intense transition is calculated at 347 nm (f = 0.137)
34
and a second only slightly weaker transition is calculated at 348 nm (f = 0.095) arising
from mainly the Re2  (HOMO-4) in the latter and also from the Re2  (HOMO–2) in the
former to the aforementioned combinations of LUMO, LUMO+1, LUMO+2, and
LUMO+3. These predicted transitions and their oscillator strengths correlate well with
the observed bands in the visible spectrum both in terms of energy and intensity. They
may be contrasted with the M2  to ligand * transitions of related molybdenum and
tungsten complexes that have f ~ 1.0 and values of ~ 10,000-50,000 M-1cm-1 in the
visible region and even more intense bands,  ~ 75,000 M-1cm-1 where the 1MLCT occurs
in the NIR.20,60
35
Absorbance / a.u.
0.008
0.006
0.004
0.002
400
500
600
700
800
900
Calculated Oscillator Strength / f
0.010
0.000
1000
Wavelength / nm
Absorbance / a.u.
0.20
0.15
0.10
0.05
400
600
800
Calculated Oscillator Strength / f
0.25
0.00
1000
Wavelength / nm
Figure 2.5 Absorption spectra of Re2(dppm)2(O2CC6H4NO2)2Cl2 in CH2Cl2 and
calculated electronic transitions of singlet ground state. (Top) is an enlarged view of
bottom spectrum from 400-1000 nm.
36
Table 2.3 Orbital contributions of electronic transitions of
Re2(dppm)2(O2CC6H4NO2)2Cl2 singlet ground state.
Figure 2.6 Calculated orbitals of Re2(dppm)2(O2CC6H4NO2)2Cl2 involved in transitions
that are not shown in Figure 2.5.
Calculations were also carried out on Re2(O2CC6H4-p-NO2)4Cl2 which converged
in the Ci point group and the idealized gas phase structure is shown in Figure 2.7. The
molecule has a typical paddle-wheel structure with axial chloride ligands and notably the
p-nitrobenzoate groups are planar and aligned along the MM axis. The calculated Re-Re
distance is 2.291 Å which is slightly longer than the experimental distance observed for
Re2(O2CPh)4Cl2, 2.235(2) Å.61 The Re-O distances are 2.08 and 2.03 Å and Re-Cl
37
distances 2.454 Å, similar to the bond lengths observed in crystal structures of related
complexes, Re2(O2CPh)4Cl2 and Re2(O2CtBu)4Cl2.61,62
Figure 2.7 Guassview plot of the optimized ground state structure of
Re2(O2CC6H4NO2)4Cl2 with Ci symmetry.
The HOMO of of Re2(O2CC6H4NO2)4Cl2 is a  type orbital that is Re-Re bonding
and Re-Cl antibonding at an energy of -7.01eV, and the HOMO-1 is the Re2  orbital
calculated at -7.17eV. The HOMO-2 / HOMO-3 are the Re-Re  bonding MOs with ReCl * character. The LUMO is Re2 * at -4.54 eV and LUMO+1 is a Re-Re * with a
mixture of Cl p lone pairs at -3.74eV. The LUMO+2 and +3 are calculated at -3.62eV
and -3.61eV and are the p-nitrobenzoate * combinations. A frontier MO energy level
diagram and Gaussview representations of these orbitals are shown in Figure 2.8. It
38
should also be noted that the occupied frontier orbitals of this molecule are similar to
those previously calculated for the pivalate analog. 63
-3
LUMO + 1
LUMO + 2
LUMO + 3
Energy (eV)
-4
LUMO
- 4.54 eV
-5
HOMO
-7
- 7.01 eV
-8
HOMO - 1
HOMO - 2
HOMO - 3
Figure 2.8 Energy diagram showing frontier orbitals of Re2(O2CC6H4NO2)4Cl2 ground
state (isovalue = 0.03).
Time-dependent DFT calculations for the quadruply bonded complex predict a
very weak HOMO to LUMO transition at 972 nm (f = 0.0002) and a Re2  to *
transition at 659 nm with f = 0.0032. Given the very weak nature of these transitions and
39
the extremely low solubility of the Re2(O2CC6H4-p-NO2)4Cl2 complex is THF and
DMSO it is not surprising that these bands were not observed experimentally. The most
intense absorption in the visible region is calculated at ~ 400 nm (f = 0.46) from the M2 
(HOMO-1) to ligand * orbitals (LUMO+2 and LUMO+3), 1MLCT, which agrees well
with the observed spectra (Figure 2.9-2.10 and Table 2.4).
Effectively this is the
counterpart to the intense M2  to L * observed for the molybdenum and tungsten
analogs, but its intensity is weaker than for M = Mo or W because of the larger energy
separation between the orbitals. At -7.17 eV the Re2  orbital is more tightly bound than
the Mo2  at ~ -5.0 eV or the W2 d at ~ -4.5 eV and this overlap with the ligand *
orbitals is greatly reduced.20 This in part is reflected in the effective positive charge on
the metals M24+ vs. Re26+.
In summary, the calculations support the observed electronic absorption spectra
and provide a basis to explain why the group 6 metals with the M24+ core are unique in
showing intense low energy MLCT absorption peaks with the -accepting carboxylate
ligands.
40
Absorbance / a.u.
1.2
1.0
0.8
0.6
0.4
0.2
Calculated Oscillator Strength / f
1.4
0.0
200
300
400
500
600
700
800
Wavelength / nm
Figure 2.9 Absorption spectra of Re2(O2CC6H4NO2)4Cl2 in THF and calculated
electronic transitions of singlet ground state.
Table 2.4 Orbital contributions of electronic transitions of Re2(O2CC6H4NO2)4Cl2 singlet
ground state. H = HOMO, L = LUMO.
41
* L+4
* H-17
L+6
H-22
L+18
H-27
Figure 2.10 Calculated orbitals of Re2(O2CC6H4NO2)4Cl2 involved in transitions that are
not shown in Figure 2.8.
2.6
Electrochemical Studies
The compound Re2(dppm)2(O2CC6H4-p-NO2)2Cl2 was examined by both cyclic
voltammetry and differential pulse voltammetry in THF. There is a reversible oxidation
wave at -0.08 V, versus the Cp2Fe0/+ couple corresponding to the metal based oxidation
and removal of an electron form the * orbital. This can be compared to the acetate
analog which under the same conditions shows a reversible oxidation at -0.26 V. We
attribute the approximately 0.2V difference in oxidation potentials to the greater electron
withdrawing properties of the p-nitrobenzoate ligands in comparison to acetate, supported
by the calculated energy difference between the HOMOs of the complexes (Figure 2.11
and Table 2.5).19 The p-nitrobenzoate complex also shows a reversible wave at -1.53 V
assigned to the placement of an electron into the LUMO which has some p-nitrobenzoate
character. In contrast the acetate analog shows a quasi-reversible reduction at -2.05 V.
42
These observations are also consistent with expectations based on the energy difference
between the LUMOs of the two complexes from the electronic structure calculations and
the frontier orbital energy diagram shown in Figure 2.4.
Current / nA
2000
1000
0
-1000
-2000
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
Voltage / V
Figure 2.11 Differential pulse voltammagrams of Re2(dppm)2(O2CR)2Cl2 in THF where
R = CH3 (orange) and R = C6H4NO2 (blue). Potentials are reported versus the Cp2Fe0/+
couple.
Table 2.5 Electrochemical oxidation and reduction potentials of
compounds in THF versus Cp2Fe0/+ couple.
43
2.7
Emission Spectra
We attempted to measure the emission spectra of both dppm containing
complexes, Re2(dppm)2(O2CR)2Cl2, where R = O2CCH3 and O2CC6H4-p-NO2, for their
emissive properties with excitation at 785 and 405 nm. However, emission was not
detected from either compound at room temperature or at 77K (liquid N2). By contrast
the quadruply bonded complex Re2(O2CC6H4-p-NO2)4Cl2 showed structured emission at
77K with maximum at 1120 nm and vibronic spacing of ~ 300 cm-1 with 405 nm
excitation, assigned as arising from the Re2 * triplet state and the vibronic features to
(ReRe).34,64 The emission spectrum at 77K is shown in Figure 2.12.
1.2
Normalized Intensity
1.0
0.8
0.6
0.4
0.2
0.0
12000
10000
8000
6000
Energy / cm-1
Figure 2.12 Near-IR emission spectrum of Re2(O2CC6H4NO2)4Cl2 in 2-Me-THF at 77K
(exc = 405 nm).
44
It is interesting to note that the 3* state of Re2(O2CC6H4NO2)4Cl2 lies ~ 3000
cm-1 lower in energy than that of the related complex Re2(p-OCH3form)4Cl2 [pOCH3form = (p-CH3OC6H4)NCHN(p-CH3OC6H4)] which emits at ~ 840 nm from a 3*
state.
However, the Re2(O2CC6H4NO2)4Cl2
3
* is close in energy to that of
dimolybdenum tetracarboxylates which show emission at ~1100 nm.45,46
the Re2(O2CR)4Cl2
3
*
The fact that
state lies at lower energy compared to the Re2(p-
O2CH3form)4Cl2 can be explained by the weaker interaction between the more
electronegative oxygen atoms of the carboxylates versus the nitrogen atoms of the
formamidinates and the Re2 * orbital.45,47
2.8
Transient Absorption Spectroscopy
We have probed the excited states of the complexes Re2(dppm)2(O2CR)2Cl2,
where R = O2CCH3 and O2CC6H4-p-NO2, by femtosecond (fs) and nanosecond (ns)
transient absorption spectroscopy. Re2(dppm)2(O2CCH3)2Cl2 has a short lived state with
 = 2.3 ps; after 2 ns vestiges of positive signal remain with maximum at ~ 400 nm which
due to current instrument detection limitations cannot be fully characterized or quantified
and
warrants
further
investigation
(Figure
2.13).
In
contrast,
Re2(dppm)2(O2CC6H4NO2)2Cl2 has one short lived state,  = 1.6 ps, and a longer lived
state with  ~10 ns. The fs broadband TA spectra of Re2(dppm)2(O2CC6H4NO2)2Cl2 is
given in Figure 2.14, which shows that the initially-populated state absorbs at 435 nm and
this feature shifts to 455 nm within 1-2 ps. The absorption at 455 nm is coincident with
that of the p-nitrobenzene radical anion, supporting the view that the longer lived excited
state has significant MLCT character.65
45
Figure 2.13 fs-TA broadband spectrum of Re2(dppm)2(O2CCH3)2Cl2 in THF (exc = 365
nm). Kinetic trace at 415 nm shows  = 2.3 ± 0.1 ps.
Figure 2.14 fs-TA broadband spectrum of Re2(dppm)2(O2CC6H4NO2)2Cl2 in THF (exc =
365 nm). Kinetic trace at 415 nm shows = 1.6 ± 0.2 ps.
46
2.9
Conclusion
This comparative study shows that in the case of Re26+, which has a quadruple
bond and an electron configuration similar to Mo24+ and W24+, 242, the  orbital is
much lower in energy compared to those of the Mo24+ and W24+ cores because of the
increased positive charge and the natural change that occurs in progressing from left to
right across the transition series. The HOMO to LUMO transition therefore is not a
MLCT transition but rather occurs from a Re2 orbital to a Re2 * orbital calculated to
occur at 972 nm. The DFT calculations reveal that the orbital in the Re26+ complex is
the HOMO–1 and the Re2 to benzoate * transition occurs at 397 nm.
The * orbital energy of the triply bonded Re24+ complexes with configuration
242*2 at ~ -5.7 eV is closer to that of the Mo24+ orbital but has the wrong symmetry
to allow the HOMO to LUMO MLCT transition; note the calculated oscillator strength
for the HOMO-LUMO transition is 0.0004 in contrast to the M2  to ligand LUMO for M
= Mo or W where f ~ 0.8 to 1.1. The orbital in the Re24+ complexes is the HOMO–4
and the Re24+ to benzoate transition occurs at higher energy, 348 nm.
In terms of photovoltaic light harvesting, Re24+ and Re26+ cores hold less promise
in relation to the M24+ cores, where M = Mo2, MoW, or W2, which lead to 1MLCT
absorptions that traverse the solar emission spectrum.20,52,66
With regards to the
population of excited states that have MLCT character for charge injection, neither the
Re24+ complexes nor the Re26+ complex exhibit a MLCT state as their lowest energy
singlet excited state. The Re24+ complex clearly exhibits a 3* state as its lowest energy
triplet state, similar to Mo24+, and some W24+ complexes.16
47
However, the
Re2(dppm)2(O2CC6H4NO2)2Cl2 complex exhibits a long lived excited state ( ~ ns) that
based on the appearance of the transient absorption, may have some ligand character.
Further studies need to be conducted to determine if this is an efficient charge injection
state.
2.10 Experimental Section
2.10.1 Materials and Methods
1
HNMR spectra were recorded on a 400MHz Bruker DPX Advanced400
spectrometer.
Samples were prepared in dry, degassed solvents in J. Young tubes.
Chemical shifts are referenced to the residual solvent peak.
Matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass
spectra were obtained on a Bruker Microflex mass spectrometer provided by a grant from
the Ohio BioProducts Innovation Center. The spectrometer was operated in a reflective,
positive ion mode. Dithranol was used as the matrix and prepared as a saturated solution
in THF. Microanalysis was performed by Atlantic Microlab Inc.
Cyclic and differential pulse voltammograms were collected at a scan rate of
50.00 and 36.36 mV s-1 respectively, using a Princeton Applied Research (PAR) 173A
potentiostat-galvanostat equipped with a PAR 176 current-to-voltage converter.
Electrochemical measurements were performed under an inert atmosphere in a 0.1 M
solution of nBu4NPF6 in THF inside a single-compartment voltammetric cell equipped
with a platinum working electrode, a platinum wire auxiliary electrode, and a pseudo
reference electrode consisting of a silver wire in 0.1 M nBu4NPF6/THF separated from the
bulk solution by a Vycor tip. The potential values are referenced to the FeCp2/FeCp2+
couple.
48
All room temperature photophysical experiments were carried out on sample
solutions sealed in 1 cm x 1 cm quartz cuvettes sealed with Kontes taps. Low
temperature photophysical experiments were carried out on 2-MeTHF sample solutions
in J. Young NMR tubes cooled with liquid N2 in a glass dewar. Electronic absorption
spectra at room temperature were recorded on a Hewlett-Packard diode array
spectrometer (HP8453). Steady-state NIR-luminescence spectra were collected on a
home-built instrument utilizing a germanium detector. The samples were excited at 405
nm (45 mW) and 785 nm (45 mW). A RG830 long pass filter was placed between the
sample and the detector.
In the femtosecond transient absorption experiments, the sample was excited at
365 nm with excitation power ~ 1 – 2 μJ at the sample. Using standard glove box
techniques, samples were prepared having an absorbance ~ 0.4 - 0.8 at the excitation
wavelength and contained in a 10.0 X 1.0 mm quartz cuvette (starna cells, inc.) that was
modified with a Kontes stopcock. The laser and detection systems that were used have
been described in detail previously.67 During the measurements, the samples were kept in
constant motion by manual movement of an XYZ stage in the vertical and horizontal
directions. In order ensure that no photodecomposition occurred during data collection,
absorption spectra were recorded before and after the transient absorption measurements.
The measurements were repeated five times at each of the pump-probe delay positions to
confirm data reproducibility throughout the experiment and the resulting spectra were
corrected for the chirp in the white-light super continuum. The kinetics were fit to a
single exponential decay of the form, S(t) = A*exp(-t/τ) + C, with amplitude, A, lifetime,
49
τ, and offset, C, using SigmaPlot 10.0. Error bars for the lifetimes are reported as the
standard error of the exponential fit.
Nanosecond transient absorption spectra were measured on a home-built
instrument, described in detail previously, pumped by a frequency tripled (355 nm)
Spectra-Physics GCR-150 Nd:YAG laser (fwhm ~ 8ns, ~ 5 mJ per pulse).68
2.10.2 Computational Methods
The geometries of the model compounds were optimized in the gas-phase using
density functional theory (DFT) with the aid of the Gaussian03 suite of programs. The
B3LYP functional was used along with the SDD energy consistent pseudopotentials for
Re, 6-31G* basis set for H, C, O, and N, and 6-31+G(2d) for P and Cl. Optimizations of
the singlet ground states were performed in C2 symmetry for the
Re2(HPCHPH)2(O2CR)2Cl2 model compounds and CI symmetry for
Re2(O2CC6H4NO2)4Cl2 and were confirmed to be minima on the potential energy surface
by frequency analysis. All Gauss View plots are shown with isovalue 0.03. The time
dependant DFT calculations produced the singlet excited states of each complex starting
with the optimized singlet ground state geometry.69
2.10.3 X-ray Crystallography
Crystallographic data for Re2(dppm)2(O2CC6H4NO2)2Cl2 were collected at 150K
on a D8 goniostat equipped with a Bruker APEXII CCD detector at Beamline 11.3.1 at
Advanced Light Source (Lawrence Berkeley National Laboratory) using synchrotron
radiation tuned to  = 0.7749 Å.70 A series of 7 second data frames measured with a
frame width of 0.2o in  were collected to calculate a unit cell. For data collection,
50
frames were measured with a frame width of 0.3o in  and an exposure time of 7 seconds
per frame out to a maximum 2 value of ~58o. The data frames were collected using the
program APEX2 and integrated using the program SAINT within APEX2. The data were
corrected for absorption and beam corrections based on the multi-scan technique as
implemented in SADABS.71 The structure was solved by the direct methods procedure in
SHELXS-97.72 Full-matrix least-squares refinements based on F2 were performed in
SHELXL-97, as incorporated in the WinGX package. The rhenium complex contains a
crystallographic two-fold rotation axis. The asymmetric unit consists of half of the Re
complex and one solvent molecule of THF.72,73 The hydrogen atoms were included in
the model at calculated positions using a riding model with U (H) = 1.2 * Ueq(attached
atom). The final refinement cycle was based on 6692 intensities and 415 variables, and
resulted in agreement factors of R1(F) = 0.104 and wR2(F2) = 0.120. For the subset of
data with I > 2*sigma (I), the R1(F) value is 0.050 for 4112 reflections. The final
difference electron density map contains maximum and minimum peak heights of 1.51
and -2.24 e/Å3. Neutral atom scattering factors were used and include terms for
anomalous dispersion.74
2.10.4 Synthesis
All reaction procedures were carried out under an inert atmosphere in a nitrogen
filled glovebox or on a Schlenck line under argon. Solvents were dried, distilled and
degassed before use. Solvents were stored over 4Å molecular sieves in pots sealed with
Kontes taps. Tetrabutylammonium octachlorodirhenate(III) and 4-nitrobenzoic acid
(98%) were purchased from Sigma-Aldrich and used as received.
Bis(diphenylphosphino)methane (97%) was purchased from Acros and used as received.
51
Re2(O2CCH3)4Cl2 and Re2(dppm)2(O2CCH3)2Cl2 were prepared according to previously
published procedures.18,19
Re2(dppm)2(O2CC6H4NO2)2Cl2. Re2(dppm)2(O2CC6H4NO2)2Cl2 was
synthesized using a carboxylate exchange similar to that previously published.19
Re2(dppm)2(O2CCH3)2Cl2 (0.1369 g, 0.1028 mmol) and p-nitrobenzoic acid (0.0395 g,
0.2360 mmol) were heated at 35oC in 25 ml methanol for 43 hours. The dark brown
product was separated from the mother liquor by filtration. The solid was washed with
toluene (2 x 1 ml), ethanol (2 x 1 ml), and ether (2 x 3 ml). Recrystallization from THF
yielded crystals suitable for X-ray crystal diffraction. Yield: 0.0550 g (34.5%)
Microanalysis: Found, C, 49.54; H, 3.52. C64H54Cl2N2O8P4Re2 requires C, 49.71; H,
3.52%. MALDI-TOF: Found: 1548.2, 1512.9. Re2(dppm)2(O2CC6H4NO2)2Cl2 requires
M+, 1546.13; M+-Cl, 1511.16. UV-Vis max (CH2Cl2/nm, values in parentheses/M-1cm1
): 789 (150), 480 sh, 369 (10900), 300 sh.
Re2(O2CC6H4NO2)2Cl2. 4-nitrobenzoic acid (0.0430 g, 0.258 mmol) was taken
up in 20 ml methanol and added to Re2(O2CCH3)4Cl2 (0.0978 g, 0.143 mmol). The
solution was stirred at 42oC for 2 days. As no significant color change was observed,
heat was increased to 60oC for 2 days. Orange solid was collected on frit and washed
with 1 x 5 ml aliquots of methanol and hexanes. MALDI-TOF: Found: 1073.2, 965.4.
Re2(O2CC6H4NO2)4Cl requires 1070.93 and Re2(O2CC6H4NO2)3(O2CCH3)Cl requires
963.93.
An excess of 4-nitrobenzoic acid (0.224 g, 1.338 mmol) was added to the
previous product and the mixture and was refluxed at 130oC for three days in 15 ml
dichlorobenzene and 1 ml tetrahydrofuran. The solvent was then decanted and brown
52
solid was washed with hexanes. Excess p-nitrobenzoic acid was sublimed out of the
product at 100oC under vacuum. MALDI-TOF: Found: 1071.6, 964.5.
Re2(O2CC6H4NO2)4Cl requires 1070.93 and Re2(O2CC6H4NO2)3(O2CCH3)Cl requires
963.93.
2.11 Acknowledgements
Special thanks to the Advanced Light Source (ALS), The Lawrence Berkeley
National Lab, and Dr. Jeanette Krause of the University of Cincinnati for the
crystallographic data collection. Thanks to the Ohio Supercomputer Center for
computing support.
53
CHAPTER 3
3. COMPARISON OF ELECTRONIC AND PHOTOPHYSICAL PROPERTIES
OF QUADRUPLY BONDED DIMETAL COMPLEXES WITH THIENYL
ETHYNYL CARBOXYLATE AND THIENYL VINYL CARBOXYLATE
LIGANDS
3.1
Introduction
Conjugated organic molecules and polymers have been the focus of much
research for application in molecular wires and optoelectronics such as FETs, LEDs, and
photovoltaics because of their ability to facilitate electronic delocalization by conducting
electrons through their  system.75-77 Introducing metal atoms into conjugated organics
allows for alteration and enhancement of electronic and optical properties: charge
delocalization and charge transport can be enhanced2, frontier orbital energeties and
thereby band gaps can be tuned2, as can emission energies78, and efficient intersystem
crossing can be achieved to access longer lived triplet excited states2.
The most basic conjugated organic units and polymers are the olefinic (polyene)
and acetylenic (polyyne) groups. These units have been compared in larger organic
structures and in metal complexes to evaluate their ability to facilitate electronic coupling
and to enhance photovoltaic cell efficiencies. It has been shown that when the olefinic or
acetylenic unit are placed as part of a linker between two metal fragments such as [Fe(5C5R5)(dppe)2] or [Ru3O(OAc)6(py)2], where dppe = diphenylphosphinoethane, OAc =
54
acetate, and py = pyridine, the (C≡C) unit is more efficient at allowing communication
between the metal centers.79-81 A possible explanation for the increased coupling is that
the metal centers are brought ~ 0.5 - 1.0 Å closer when bridged with the acetylenic
linkers versus the corresponding olefinic linkers.79-81
With this information in mind we were curious as to how vinyl and ethynyl units
would affect the electronic coupling and photophysical properties of quadruply bonded
dimetal complexes. Bis-bis complexes, trans-M2(TiPB)2(O2CTh)2, where Th = thiophene
and M = Mo or W, have already been examined and have shown interesting electronic
and photophysical properties52,82, therefore these molecules were used as a core into
which C≡C and C=C units could be inserted and compared. This chapter focuses on the
synthesis, electronic structure, and photophysical properties of the bis-bis complexes
M2(TiPB)2(O2CC≡CTh)2 and M2(TiPB)2(O2CCH=CHTh)2, where M = Mo and W.
3.2
Synthesis
p-Tolylethynylcarboxylic acid was prepared via carboxylation of
and
Anthrylethynylcarboxylic acid was commercially available and the 3-(2-thienyl)propiolic
acid was synthesized via Corey’s method from the corresponding aldehyde.83
The
compounds were prepared by reacting the homoleptic compound M2(TiPB)4 and 2
equivelents of acid in toluene. The steric bulk of the TiPB ligands results in a trans
substituted complex, see Figure 3.1, that precipitates out of solution upon formation. The
microcrystalline precipitates that formed were collected and washed with toluene and
hexanes and dried under vacuum.
They gave molecular ions in the mass spectra
(MALDI-TOF) and showed 1H NMR spectra consistent with the formulation of the transM2(TiPB)2L2 compounds as the major product.
55
Figure 3.1 Synthetic route to heteroleptic bis-bis dimetal complexes.
3.3
Electronic Absorption Spectra
The electronic absorption spectra of all four complexes in THF are shown in
Figure 3.2. The M2(TiPB)2(O2CC≡CTh)2 complexes exhibit an intense absorption at ~
295 nm arising from the thienylethynylcarboxylate  to * transition, while in the
M2(TiPB)2(O2CCH=CHTh)2 complexes this  to * transition occurs at slightly lower
energy ~ 308 nm. All four complexes show a broad intense 1MLCT band as the lowest
energy absorption band with the maxima shifting to lower energies as the ligand is
changed from thienylethynylcarboxylate to thienylvinylcarboxylate and on going from
Mo to W.
56
Normalized Absorbance / a.u.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
700
800
900
Wavelength / nm
Figure 3.2 Electronic absorption spectra of Mo2(TiPB)2(O2CC≡CTh)2, max = 476 nm
(orange); Mo2(TiPB)2(O2CCH=CHTh)2, max = 515 nm (red); W2(TiPB)2(O2CC≡CTh)2
max = 646 nm (blue); and W2(TiPB)2(O2CCH=CHTh)2, max = 750 nm (green) in THF
at room temperature.
3.4
Electronic Structure Calculations
Electronic structure calculations, using density functional theory (DFT), were
conducted on the model complexes M2(O2CH)2(O2CR)2, where R = C≡CTh, and
CH=CHTh; the complexes were optimized in the Ci and C2h point groups respectively.
The energy levels of the frontier orbitals and the molecular orbital plots of these model
complexes can be seen in Figure 3.2 and 3.3, respectively. In all cases the HOMO is the
M2  orbital and the LUMO is the in phase * orbital of the ligand. In the case of
Mo2(O2CH)2(O2CCH=CHTh)2,
W2(O2CH)2(O2CCH=CHTh)2,
and
W2(O2CH)2(O2CCH=CHTh)2 the LUMO+1 (L+1) is the ligand * out of phase
57
combination, while in Mo2(O2CH)2(O2CC≡CTh)2 this ligand * is the LUMO + 2 and the
Mo2 * is the LUMO+1.
W2(O2CH)2(O2CCH=CHTh)2, and
The LUMO+2 in Mo2(O2CH)2(O2CCH=CHTh)2,
W2(O2CH)2(O2CCH≡CHTh)2 is the M2 *
orbital. Below the HOMO (HOMO-1,2 for Mo2 and HOMO-3,4 for W2) lie the ligand in
and out of phase  orbitals. It can be seen that the ligand in-phase  and * orbitals are
not of the proper symmetry to interact with the metal center in any way, however, the
out-of-phase  and * orbitals of the ligand can interact with the  orbital of the metal.
The ligand  orbitals can donate electron density to the metal center, destabilizing it,
while the ligand * orbital can accept electron density from the metal center via
backbonding, stabilizing the  orbital and destabilizing the ligand * orbital. The energy
separation between the in-phase and out-of-phase * orbitals gives a qualitative
indication of the degree of backbonding and the amount of communication occurring
between the metal center and the ligand. It can be seen when comparing the energy
separation in Mo2(O2CH)2(O2CCH=CHTh)2, Mo2(O2CH)2(O2CC≡CTh)2, and previously
published Mo2(O2CH)2(O2Th)282 there is very little difference (E = 0.25, E = 0.29 eV,
and E = 0.29 eV respectively). The tungsten complexes are similar in that the energy
difference between the in-phase and out-of-phase * orbitals are comparable to each
other (E = 0.37 eV for W2(O2CH)2(O2CCH=CHTh)2, E = 0.41 eV for
W2(O2CH)2(O2CC≡CTh)2, and E = 0.40 eV for W2(O2CH)2(O2CTh)2)2)82; however, the
separation is 0.12 eV greater than that for the molybdenum analogs.
This can be
explained by the fact that tungsten’s orbitals are higher in energy than molybdenum’s
allowing for better energetic overlap with the ligand * orbitals, leading to stronger
58
mixing. Table 3.1 compares the calculated energies of the HOMOs for these complexes
as well as the previously published M2(O2CH)2(O2CTh)2 complexes.82 Examination of
the calculated HOMO energies reveals that the addition of the CH=CH group between
the thienyl and carboxylate moieties results in a destabilization of the HOMO while the
C≡C group results in a stabilization.
Table 3.1 Electrochemical Potentials and Calculated Energies
The time dependent calculations were conducted as well to assist in the
assignments of the bands seen in the electronic absorption spectra. The significant
transitions (oscillator strengths greater than 0.1) are given in Table 3.1. In three of the
complexes
Mo2(O2CH)2(O2CC≡CTh)2,
W2(O2CH)2(O2CC≡CTh)2,
and
W2(O2CH)2(O2CCH=CHTh)2, the lowest energy calculated transition occurs solely
between the  based HOMO to the thienyl ligand in-phase * based LUMO. In the case
of Mo2(O2CH)2(O2CCH=CHTh)2 the two lowest energy transition arises mainly from
promoting an electron from the  based HOMO to the thienyl ligand * LUMO, however
59
there are also contributions to this transition from H-4 (M2 ) → L+3 (M2 *), H-3 (M2
) → L+4 (M2 *), and H → L+2 (*). This confirms the assignment of the lowest
energy absorption band in all the complexes as MLCT from the  to the * of the
thienylvinyl or thienylethynyl based ligand. The next major transition calculated in all
four complexes occurs by promoting an electron from the M2  HOMO to the in-phase
* orbitals of the formate carboxylate ligands (L+6 in the Mo2 complexes and L+4 in the
W2 complexes). Experimentally in the Mo complexes this transition is obscured by
stronger transitions, however it can be seen as a weak transition in the W complexes ~
400 nm.
The most intense higher energy transition in Mo2(O2CH)2(O2CC≡CTh)2 is
calculated to occur at 299 nm (f = 0.725) and is composed of H → L+8 (O2CC≡CTh L
*), H-3 (M2 ) → L+2 (O2CC≡CTh* and some M2 *), and most significantly H-2
(O2CC≡CTh L  and M2 ) → LUMO. Similarly in the Mo2(O2CH)2(O2CCH=CHTh)2
complex the transition calculated at 304 nm (f = 0.517) from mainly H-1 (O2CCH=CHTh
) → L+1 (O2CCH=CHTh* and some M2 *) and also H → L+8 (O2CCH=CHTh ).
W2(O2CH)2(O2CC≡CTh)2 has a calculated transition at 296 nm from H-4 (O2CC≡CTh )
→ L, H-3 (O2CC≡CTh ) →
L+1 (O2CC≡CTh* and some M2 *), H → L+7
(O2CC≡CTh*), and H→ L+9 (O2CC≡CTh*). W2(O2CH)2(O2CCH=CHTh)2 has a
calculated transition at 290 nm from mainly thienylvinylcarboxylate  based orbitals to
thienylvinylcarboxylate * based orbitals H-7(Th ) → L (O2CCH=CHTh *), H-4
(O2CCH=CHTh  + M2 d) → L (O2CCH=CHTh *), H-3 (O2CCH=CHTh ) → L+1
(O2CCH=CHTh *), and a small contribution from H → L+8 (O2CCH=CHTh *).
60
These time dependent calculations support the assignment of the experimental absorption
bands at ~295 nm and ~308 nm as thienylethynylcarboxylate ligand -* and
thienylvinylcarboxylate ligand -*, respectively.
Figure 3.3 Calculated energy diagram of frontier orbitals of M2(O2CH)2(O2CC≡CTh)2
and M2(O2CH)2(O2CCH=CHTh)2, where M = Mo, W.
61
Figure 3.4 Molecular orbital plots of frontier orbitals for M2(O2CH)2(O2CC≡CTh)2 and
M2(O2CH)2(O2CCH=CHTh)2, where M = Mo, W; isosurface value of 0.02.
62
Table 3.2 Orbital contributions of transitions of singlet ground state of
(a) Mo2(O2CH)2(O2CC≡CTh)2 (b) Mo2(O2CH)2(O2CCH=CHTh)2
(c) W2(O2CH)2(O2CC≡CTh)2 (d) W2(O2CH)2(O2CCH=CHTh)2
63
3.5
Electrochemical Studies
In order to confirm the predictions made by DFT calculations that the energy of
the HOMO is dependent on the ligand, electrochemical studies were performed on all
four complexes. The compounds were examined by cyclic voltammetry and differential
pulse voltammetry in 0.1M Bu4NPF6/THF solutions. The DPVs in Figure 3.5 show that
Mo2(TiPB)2(O2CC≡CTh)2 is the hardest complex to oxidize at 0.256 V and that upon
changing to the thineylvinylcarboxylate ligand in Mo2(TiPB)2(O2CCH=CHTh)2, the
complex becomes easier to oxidize with an oxidation potential of -0.027 V.
The
difference in oxidation potentials of 0.283 V is similar to the calculated energy separation
of 0.23 eV. Likewise, the difference between the oxidation potentials of the two tungsten
compounds is 0.239 V, with W2(TiPB)2(O2CCH=CHTh)2 being easier to oxidize at 0.610 V than W2(TiPB)2(O2CC≡CTh)2 at -0.371 V (calculated 0.23 eV). The tungsten
complexes are easier to oxidize than their molybdenum counterparts by about 0.63 V,
reflecting the higher energy of the  orbital which is possibly due to the weaker  bond of
the tungsten complexes.9 It is also interesting to compare these oxidation values to the
previously published complexes Mo2(TiPB)2(O2CTh)2 and W2(TiPB)2(O2CTh)2 with
oxidation potentials in 0.1M Bu4NPF6/THF solutions of 0.056 V and -0.56 V,
respectively, versus Cp2Fe0/+ redox couple (see Table 3.1).82
The M2(TiPB)2(O2CCH=CHTh)2 complexes are slightly easier to oxidize than the
M2(TiPB)2(O2CTh)2 complexes, however, the M2(TiPB)2(O2CC≡CTh)2 complexes are
significantly harder to oxidize. A similar trend was observed in [(C5Me5)(dppe)2Fe]2--L
complexes where L = CH=CH-CH=CH or C≡C-C≡C; the first oxidation of an Fe center
when attached to CH=CH-CH=CH was easier to oxidize by 0.16V than when attached to
64
C≡C-C≡C.80 Likewise in the mononuclear metal complexes [(C5Me5)(dppe)2Fe-L], when
L= CH=CH2 the metal oxidation occurs at a potential 0.21 V more negative with respect
to L = C≡CH.80
It is known from the ionization energies and calculated
electronegativities that acetylene, CH≡CH, is more electron withdrawing than
CH2=CH2.84,85
Correlating well with this, the gas basicity of H2C=CH2 is greater than
that of HC≡CH.84 This knowledge, combined with what is observed in the calculated
orbital energies and electrochemistry, indicates that the CH=CH group is slightly more
electron donating, therefore the filled ligand  orbitals destabilize the filled  orbital,
whereas the C≡C group is more withdrawing which results in less donation into the metal
center and a relative stabilization of the filled metal orbital.
Figure 3.5 Oxidation DPVs of complexes Mo2(TiPB)2(O2CC≡CTh)2 (orange),
Mo2(TiPB)2(O2CCH=CHTh)2 (red), W2(TiPB)2(O2CC≡CTh)2 (blue),
W2(TiPB)2(O2CCH=CHTh)2 (green) in 0.1M Bu4NPF6/THF solution. Referenced versus
Cp2Fe0/+ redox couple.
65
The
cyclic
voltammagrams
of
Mo2(TiPB)2(O2CCH=CHTh)2
W2(TiPB)2(O2CCH=CHTh)2 are shown in Figure 3.6.
and
The CVs show reversible
oxidation waves as well quasi-reversible reduction waves which lie close to the solvent
limit. These reduction waves show a clear evidence of splitting. For M = Mo, the E1/2
for the 1st and 2nd reduction waves is ~ 0.2 V. For tungsten evidence of an impurity is
seen, possibly corresponding to the ter-substituted product, at a lower reduction potential
of two reduction waves separated by ~ 0.3 V. The latter is attributed to the major species
present in solution namely the disubstituted bis-bis complex. The magnitude of the
separation between the two reduction waves is an indication of the electronic coupling
where the relative stability of the mixed valence ion compared to the neutral and doubly
reduced species can be expressed by the comproportionation constant (Kc)86
(1)
(2)
The greater E1/2 observed for the tungsten versus molybdenum complex again
supports the greater electronic communication that occurs when the third row transition
metal is incorporated into these complexes.
66
Figure 3.6 Cyclic voltammagrams of M2(TiPB)2(O2C-CH=CHTh)2, M = Mo (red) and
W (green) in 0.1M Bu4NPF6/THF solution with respect to Cp2Fe0/+ couple. M = Mo:
E1/2RED(1) = -2.449 V, E1/2RED(2) = -2.618 V; M = W: E1/2RED(1) = -2.378 V; E1/2RED(2) = 2.723 V.
3.6
Variable Temperature Absorption
When a bis-bis complex is excited from the ground state to the 1MLCT state it can
be
thought
of
as
an
excited
state
mixed
valence
complex
(ESMV).
While the hole is localized on the M2 center, the electron is in a ligand * orbital where it
may be delocalized over both ligands or localized on one. Figure 3.7 shows a schematic
representation of the potential energy surfaces of the ground and excited states in a
weakly coupled excited state mixed valence system (Class II in the Robin and Day
scheme), a system on the Class II/III border, and a completely delocalized Class III
67
system. In the most localized case shown, Class II, the offset in nuclear configuration
from the ground state is most pronounced and two minima can be seen representing the
change as the charge is localized on one ligand (La) versus the other (Lb). As the
coupling of the ligands through the metal center increases, the barrier to electron transfer
decreases, seen in the center of Figure 3.7, and the ESMV is said to be on the Class II/III
border. The completely delocalized Class III system is shown in the final box of Figure
3.4, where the nuclear configuration changes are the smallest and the potential energy
well is almost directly nested above the ground state.
Figure 3.7 Potential energy surfaces representing the ground state (S0) and mixed
valence excited state (S1) in a weakly coupled Class II system (left), a system on the
Class II/III border (center), and in a completely delocalized Class III system (right).
Modified from ref 86.
68
The vibronic features of the MLCT absorption band can be indicative of the
degree of coupling in the bis-bis complexes where if a strongly coupled ESMV complex
is formed the offset in the nuclear configuration between the ground and excited state is
small therefore the first vibronic feature ( = 0) would be expected to be the most
intense. However, in complexes where the coupling is weaker (greater offset between
ground state and excited state nuclear coordinates), higher energy vibronic features ( >
0) would be expected to be more intense.87
The low temperature absorption spectra of the M2(TiPB)2(O2CCH=CHTh)2
complexes can be seen in Figure 3.8. At room temperature the MLCT bands are broad
and relatively featureless suggesting a broad Boltzmann distribution of rotamers in
solution.52,86 As the temperature is lowered, the rotational barrier becomes significant
with respect to thermal energy and a red shift of ca. 30 nm is observed in the MLCT band
as the planar geometry dominates. As the temperature is lowered the vibronic features
sharpen noticeably.
Their spacing supports the assignment of the lowest energy
transition being MLCT in nature as they match well with ground state vibrations of the
free ligand.88 It can be seen that in W2(TiPB)2(O2CCH=CHTh)2 the  = 0 is the most
intense while in Mo2(TiPB)2(O2CCH=CHTh)2 this is not the case. This reflects the
greater coupling in tungsten complexes due to better energy match and orbital overlap
between the W2  orbital and ligand * orbitals.
69
1.6
Absorbance / a.u.
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
300
400
500
600
700
Wavelength / nm
800
900
Figure 3.8 Electronic absorption spectra in 2-MeTHF of Mo2(TiPB)2(O2CCH=CHTh)2 at
room temperature (red dashed) and -174oC (red solid) and W2(TiPB)2(O2CCH=CHTh)2 at
room temperature (green dashed) and -175oC (green solid).
3.7
Emission Studies
When excited into the MLCT band, Mo2(TiPB)2(O2CCH=CHTh)2 exhibits a weak
fluorescence arising from the 1MLCT state in the visible region with maxima ~ 700 nm
and phosphorescence at ~1055 nm due to radiative decay of the 3* excited state, Figure
3.9. This emissive triplet state has been confirmed previously in similar molybdenum
complexes to be the 3* due to the solvent and ligand independence of the max and due
to the vibronic features which appear at 77K with spacing ~ 350-400 cm-1 matching
(MoMo).16 W2(TiPB)2(O2CCH=CHTh)2 exhibits only a single emission, fluorescence
from the 1MLCT with max ~ 850 nm, Figure 3.9. A second emission from a lower
70
energy triplet state is not seen in this complex presumably due to its relative proximity to
the ground state which leads to non-radiative decay in accordance with the energy gap
law.89
Figure 3.9 Visible (exc = 460 nm) and NIR (exc = 405nm, 785 nm) emission spectra of
Mo2(TiPB)2(O2CCH=CHTh)2 (red) and W2(TiPB)2(O2CCH=CHTh)2 (green) in THF.
3.8
Solvent Dependence
The low energy MLCT absorptions of these complexes demonstrate
solvatochromism where the absorption max for Mo2(TiPB)2(O2CCH=CHTh)2 is 470 nm
in CHCl3, 477 nm in CH2Cl2, 515 nm in THF, and 530 nm in DMSO (Figure 3.10).
Correspondingly, W2(TiPB)2(O2CCH=CHTh)2 absorption max appear at 675 nm, 679
nm, 750 nm, and 784 nm in CHCl3, CH2Cl2, THF, and DMSO respectively. A similar
solvatochromic trend is observed in the fluorescence of Mo2(TiPB)2(O2CCH=CHTh)2
where energy ofmax proceeds in the order CHCl3 ≥ CH2Cl2 > THF > DMSO. Instrument
71
detection limitations make observation of the fluorescence from
1
MLCT of
W2(TiPB)2(O2CCH=CHTh)2 in CHCl3 and CH2Cl2 difficult, however, the emission
maxima shifts to lower energy on going from THF (max ~ 750nm) to DMSO (max ~ 925
nm). The solvatochromism observed in the absorption spectra when considering the noncoordinating solvents CHCl3 and CH2Cl2 is very small, however, a large
solvatochromism is observed in the presence of donating solvents. This can be explained
by considering that THF has been seen to coordinate axially in single crystals of these
complexes.16 As the donating ability of the solvent increases from THF90 to DMSO91 the
positive charge formed on the metal center in the photoexcited state is better stabilized.92
Normalized Intensity / a.u.
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
300
400
500
600
700
800
Wavelength / nm
Figure 3.10 Absorption (dashed lines) and emission (solid lines) of
Mo2(TiPB)2(O2CCH=CHTh)2 in various solvents, CHCl3 (blue), CH2Cl2 (green), THF
(red), and DMSO (black).
72
3.9
Conclusions
This research clarifies how inserting an electron withdrawing ethynyl moiety into
the aromatic ligands of the bis-bis complexes affects the frontier orbitals by stabilizing
the filled metal orbitals and shifting the HOMO to lower energy with respect to the vinyl
containing complex. It can also be noted that insertion of the vinyl moiety causes the
ligand based reductions to occur at ~0.4 V more positive potential compared to the
M2(TiPB)2(O2CTh)2 complexes, reflecting the greater conjugation which lowers the
LUMO * energy. This research also displays the difference in the nature of the W 2 core
versus the Mo2 core and the greater degree of electronic communication that occurs in
complexes of the former.
This control of orbital energetics will be useful for
incorporating these bis-bis complexes into photovoltaic devices with various acceptor
complexes and electrodes.
3.10 Experimental
3.10.1 Materials and Methods
1
HNMR spectra were recorded on a 400MHz Bruker DPX Advanced400 spectrometer.
Samples were prepared in dry, degassed solvents in J. Young tubes. Chemical shifts are
referenced to the residual protio solvent peak.
Matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass
spectra were obtained on a Bruker Microflex mass spectrometer provided by a grant from
the Ohio BioProducts Innovation Center. The spectrometer was operated in a reflective,
positive ion mode. Dithranol was used as the matrix and prepared as a saturated solution
in THF. Electrospray ionization (ESI) was performed at the Ohio State Campus
73
Chemical Instrument Center Mass Spectrometry and Proteomics Facility with a
Micromass LCT.
Cyclic (100 mV s-1) and differential pulse (36.36 mVs-1) voltammograms were
collected using a Princeton Applied Research (PAR) 173A potentiostat-galvanostat
equipped with a PAR 176 current-to-voltage converter. Electrochemical measurements
were performed under an inert atmosphere in a 0.1 M solution of nBu4NPF6 in THF inside
a single-compartment voltammetric cell equipped with a platinum working electrode, a
platinum wire auxiliary electrode, and a pseudo reference electrode consisting of a silver
wire in 0.1 M nBu4NPF6/THF separated from the bulk solution by a Vycor tip. The
potential values are referenced to the FeCp2/FeCp2+ couple.
All room temperature photophysical experiments were carried out on sample
solutions sealed in 1 cm x 1 cm quartz cuvettes sealed with Kontes taps. Electronic
absorption spectra at room temperature were recorded on a Hewlett-Packard diode array
spectrometer (HP8453). Low temperature absorption spectra were obtained using a
Perkin-Elmer Lambda 900 UV-vis NIR spectrometer from 2-MeTHF sample solutions.
Low temperature absorption spectra were obtained with a Specac variable temperature
cryostat employing a permanently sealed liquid IR cell with CaF2 windows.
Steady-state visible luminescence spectra were recorded on a SPEX Fluoromax-2
spectrofluorimeter in UVvisible region. Steady-state NIR-luminescence spectra were
collected on a home-built instrument utilizing a germanium detector. For detecting
emission in the NIR region, the samples were excited at 405 nm and 785 nm. An 830 nm
or 695 nm long pass filter was placed between the sample and the detector. Low
74
temperature emission experiments were carried out on 2-MeTHF sample solutions in J.
Young NMR tubes cooled with liquid N2 in a glass dewar.
Nanosecond transient absorption spectra were measured on a home-built
instrument, described in detail previously68, pumped by a frequency doubled (532 nm) or
tripled (355 nm) Spectra-Physics GCR-150 Nd:YAG laser (fwhm ~ 8ns, ~ 5 mJ per
pulse).
3.10.2 Computational Methods
The geometries of the model compounds were optimized in the gas-phase using
density functional theory (DFT) with the aid of the Gaussian03 suite of programs. The
B3LYP functional was used along with the SDD energy consistent pseudopotentials for
Mo and W, 6-31G* basis set for H, C, and O, and 6-31G+(2d) for S. Optimizations of the
singlet ground states were performed in C2h symmetry for M2(O2CH)2(O2C-CH=CHTh)2
and Ci symmetry for M2(O2CH)2(O2C-C≡C-Th)2 and were confirmed to be minima on
the potential energy surface by frequency analysis. All GaussView plots are shown with
isovalue 0.02.
3.10.3 Synthesis
3-(2-thienyl)acrylic acid was purchased from Sigma-Aldrich and used as received.
3-(2-thienyl)propynoic acid was prepared according to previously published procedure.83
Mo2(TiPB)2(O2CC≡CTh)2. A solution of 3-(2-thienyl)propynoic acid (0.092 g,
0.605 mmol) in 40 ml dry, degassed toluene was added to a Schlenck flask containing a
solution of Mo2(TiPB)4 (0.360 g, 0.305 mmol) in 20 ml dry, degassed toluene. A bright
75
red solution formed immediately upon combination; the solution was allowed to stir for 7
days at which point an orange-red precipitate had formed. The supernatant liquid was
decanted and the remaining solid was washed with toluene (4 x 25 ml) and hexanes (1 x
20 ml) before being dried under vacuum to yield 0.203 g of solid. MALDI-TOF: Found:
1083.4, 1061.3, 1039.2, 987.3, 890.1. Mo2(O2CC15H23)3(O2CCCC4H3S) requires 1085.3,
Mo2(O2CC15H23)2(O2CC12H17)(O2CCCC4H3S)
requires
1042.3,
Mo2(O2CC15H23)2(O2CCCC4H3S)2 requires 988.1, Mo2(O2CC15H23)(O2CCCC4H3S)3
requires 891.9.
W2(TiPB)2(O2CC≡CTh)2. A solution of 3-(2-thienyl)propynoic acid (0.107 g,
0.703 mmol) in 25 ml dry, degassed toluene and 10 drops of THF was added to a
Schlenck flask containing a solution of W2(TiPB)4 (0.482 g, 0.355 mmol) in 25 ml dry,
degassed toluene. A bright blue solution formed immediately upon combination; the
solution was allowed to stir for 7 days at which point a blue precipitate had formed. The
supernatant liquid was decanted and the remaining solid was washed with toluene (3 x 15
ml) and hexanes (1 x 15 ml) before being dried under vacuum to yield 0.201 g of solid.
MALDI-TOF: Found: 1162.3. W2(O2CC15H23)2(O2CCCC4H3S)2 requires 1164.2.
Mo2(TiPB)2(O2CCH=CHTh)2. Mo2(TiPB)4 (0.458 g, 0.388 mmol) and 3-(2thienyl)acrylic acid (0.116 g, 0.757 mmol) were combined in a Schlenck flask with 50 ml
toluene. The reaction mixture was allowed to stir at room temperature for 4 days at
which point the supernatant was decanted and the precipitate was washed with toluene (3
x 30 ml) and hexanes (1 x 10 ml). The red solid was then dried under vacuum. Yield:
0.302 g (80%). Microanalysis found: C, 54.91; H, 5.79%. C46H56Mo2O8S2 requires C,
55.64; H, 5.68%. 1HNMR (THF-d8): H (400 MHz) 7.86 (d, 1H), 7.40 (d, 1H), 7.30 (d,
76
1H), 7.06 (dd, 1H), 6.98 (s, 2H), 6.85 (d, 1H), 3.09 (m, 2H), 2.85 (m, 1H), 1.21 (d, 6H),
1.18 (d, 12H) ppm. MALDI-TOF: Found: 992.1. Mo2(O2CC15H23)2(O2CC3H5S)2 requires
993.1.
W2(TiPB)2(O2CCH=CHTh)2. W2(TiPB)4 (0.466 g, 0.343 mmol) and 3-(2thienyl)acrylic acid (0.103 g, 0.669 mmol) were combined in a Schlenck flask with 50 ml
toluene. The reaction mixture was allowed to stir at room temperature for 4 days at
which point the supernatant was decanted and the precipitate was washed with toluene (3
x 20 ml) and hexanes (1 x 10 ml). The blue solid was then dried under vacuum.
Microanalysis found: C, 46.31; H, 5.04%. C46H56W2O8S2 requires C, 47.27; H, 4.83%.
1
HNMR (THF-d8): H (400 MHz) 7.37 (d, 1H), 7.30 (d, 1H), 7.15 (d, 1H), 7.10 (m, 1H),
7.03 (s, 1.5H), 6.95 (d, 1H), 2.92 (m, 3H), 1.24 (d, 6H), 1.17 (d, 10H) ppm. MALDITOF: Found: 1169.3, 1074.8. W2(O2CC15H23)2(O2CC3H5S)2 requires 1168.2 and
W2(O2CC15H23)(O2CC3H5S)3 requires 1076.1.
77
CHAPTER 4
4. THE ELECTRONIC AND PHOTOPHYSICAL PROPERTIES OF
QUADRUPLY BONDED DIMETAL COMPLEXES SUPPORTED BY
ARYLETHYNYLCARBOXYLATE LIGANDS
4.1
Introduction
For many years the photophysical properties of basic quadruply bonded
paddlewheel complexes have been explored. The  → * electronic transition has been
observed now in many dimolybdenum and ditungsten complexes: in homoleptic
compounds such as [Mo2(L)8]4- (L = Cl-, CH3-, NCS-), [W2(L)8]4- (L = Cl-, CH3-),
[Mo2(L)8]4+ (L = NH3, CH3CN, H2O); heteroleptic Mo2Cl4(PR3)4 and W2X4(PR3)4; as
well as in complexes with bridging ligands such as mhp (2-hydroxy-6-methylpyridine
anion).9,28,29
Emission from this singlet * state has also been observed in some of
these complexes (see Table 1.1).42-44
However, little was understood about the
photophysical properties of quadruply bonded dimetal tetracarboxylates prior to 2005.
In 2005, Byrnes et al. explored dimetal tetraarylcarboxylate complexes of
molybdenum and tungsten, observing absorption to and emission from the 1MLCT state.
Once in the 1MLCT excited state, these complexes quickly underwent intersystem
crossing to a longer lived triplet.49,50 Curiosity regarding the nature of this triplet state led
to the synthesis and exploration of the photophysical properties of the related complexes,
M2(TiPB)2(O2CC≡CR)2, where M = Mo or W and R = p-C6H4CH3 or 9-C14H9, which will
78
be discussed in this chapter.
The insertion of the C≡C unit between the aryl and
carboxylate groups offers two advantages over previous compounds. First, in the crystal
structure of Mo2(O2CC14H9)4 the anthracene units are twisted out the plane of the
carboxylate unit by 44 - 87 degrees due to steric interactions between the peri-H atoms at
the 1 and 8 positions of the anthracene and the carboxylate O atoms.49 The addition of
the acetylene linker provides a way to maintain conjugation while alleviating steric
hindrance, thus allowing greater interaction between the metal core and the  conjugated
ligands. Secondly, oligomers and polymers of these quadruply bonded metal complexes
would be interesting for the incorporation into molecular electronic and optoelectronic
devices as they offer both the advantages of conjugated organic polymers as well as the
tunability of a redox metal center.60 Alkynyl polymers have shown particular promise in
the area of optoelectronics and molecular electronics due to their -electron conjugation,
rigid, linear structure, and high stability. These properties result in polymers that exhibit
interesting luminescence, are photoconductive, display electronic communication, and
have liquid crystallinity.93 Therefore, the acetylene unit was a natural choice for an
organic moiety to be incorporated into the quadruply bonded metal complexes.
4.2
Syntheses
3-(4-Tolyl)propynoic acid was synthesized via carboxylation of commercially
available p-tolylacetylene.
3-(9-Anthracenyl)propynoic acid was synthesized two
different ways: first in limited quantities via direct carboxylation of the acetylene
derivative and secondly from the corresponding aldehyde via Corey’s method.83,94 The
metal complexes were prepared by reacting the homoleptic compound M2(TiPB)4 with
just under 2 equivelents of acid in toluene. The steric bulk of the TiPB ligands results in
79
a trans substituted complex, see Figure 4.1, that precipitates out of solution upon
formation. The microcrystalline precipitates that formed were collected, washed with
toluene
and
hexanes,
and
dried
under
vacuum.
The
target
complexes,
Mo2(TiPB)2(O2CC≡C-p-tolyl)2
(1a),
Mo2(TiPB)2(O2CC≡C-(9-anthracenyl))2
(2a),
W2(TiPB)2(O2CC≡C-p-tolyl)2 (1b), W2(TiPB)2(O2CC≡C-(9-anthracenyl))2 (2b),
gave
molecular ions in the mass spectra (MALDI-TOF) and showed 1H NMR spectra
consistent with the formulation of the trans-M2(TiPB)2L2 compounds as the major
product, although in some cases minor formation of a tris-substituted species was
observed in the mass spectra.
Figure 4.1 Synthetic route to heteroleptic bis-bis dimetal complexes, where R' represents
C≡C-p-tolyl or C≡C-9-anthracenyl.
4.3
Single Crystal Structure of 1a [Mo2(TiPB)2(O2CC2C6H4CH3)2∙4THF]
An ORTEP drawing of Mo2(TiPB)2(O2CC2C6H4CH3)2∙4THF is given in Figure
4.2 and a summary of crystallographic data is given in Table 4.1. The space group of the
single crystal is Pī. The dimer contains an inversion center and a THF molecule is
80
bonded to each of the Mo atoms in the axial position through long Mo∙∙∙O interactions of
2.617(2) Å. The Mo-Mo distance of 2.1043(4) Å, is typical of a Mo-Mo quadruple
bond,9 and the four unique Mo-O bonds range from 2.103(2)-2.112(2) Å. It can be seen
that due to the steric bulk of the isopropyl groups, the TiPB ligand is twisted out of the
plane of the metal atoms with a dihedral angle between the O2C and C6 planes of
90.7(3)o. However, the tolyl C6 ring lies in the same plane as the Mo-Mo bond, with a
O2C and C6 dihedral angle of 3.5(3) degrees.
Figure 4.2 ORTEP drawing of Mo2(TiPB)2(O2CC2C6H4CH3)2∙4THF (1a) drawn with
50% probability ellipsoids. Hydrogen atoms are omitted for clarity. The solvent
molecules of THF are shown here. The Mo complex contains an inversion center.
81
Table 4.1 Crystallographic details for Mo2(TiPB)2(O2CC2C6H4CH3)2∙4THF
Molecular formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
C68 H92 Mo2 O12
1293.30
150(2) K
0.71073 Å
triclinic
P1
a = 10.9166(1) Å
b = 11.6291(1) Å
c = 13.4313(2) Å
Volume
1621.77(3) Å
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
1
3
1.324 Mg/m
0.446 mm-1
680
3
0.08 x 0.15 x 0.23 mm
2.53 to 27.52°
-14<=h<=14, -15<=k<=15, -17<=l<=17
42565
7415 [R(int) = 0.043]
Completeness to theta = 27.52°
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole
99.4 %
2
Full-matrix least-squares on F
7415 / 0 / 376
1.053
R1 = 0.0368, wR2 = 0.0925
R1 = 0.0516, wR2 = 0.0987
3
0.792 and -0.739 e/Å
 = 78.634(1)°
 = 84.373(1)°
= 76.304(1)°
3
82
4.4
Electronic Structure Calculations
Electronic structure calculations, using density functional theory (DFT), were
conducted on the model complexes M2(O2CH)2(O2CR)2, where R = C≡Ctolyl and
C≡Canthracenyl; the complexes were optimized in the C2 and D2h point groups,
respectively. To conserve computational resources and due to the fact that the TiPB
ligands are twisted out of the metal-metal carboxylate plane in these complexes, thereby,
minimizing -bonding interactions, formate ligands were substituted in place of the TiPB
ligands. The energy levels of the frontier orbitals and the molecular orbital plots of these
model complexes can be seen in Figure 4.3 and 4.4, respectively.
Figure 4.3 Energy diagram displaying the calculated energies of the frontier orbitals of
the ground states of 1a, 1b, 2a, and 2b. 1a and 1b were optimized in C2 symmetry and 2a
and 2b were optimized in D2h symmetry.
83
Figure 4.4 Frontier orbitals of the ground states of 1a, 1b, 2a, and 2b. 1a and 1b were
optimized in C2 symmetry and 2a and 2b were optimized in D2h symmetry. Note: W2 
orbitals of 1b not shown; energetically these orbitals are between the filled ligand  and
W2 .
In all cases the HOMO is the M2  orbital and the LUMO is the in-phase *
orbital of the ligand.
The LUMO+1 and LUMO+2, with the exception of complex 1a,
are the out-of-phase * orbital of the ligand and the M2 * orbital, respectively. In the
case of 1a the LUMO+1 is the M2 * orbital and LUMO+2 is the out-of-phase *. In all
cases, with the exception of 1b, the HOMO-1 and HOMO-2 are the filled ligand in-phase
and out-of-phase  orbtials. For 1b, the HOMO-1 and HOMO-2 are M2  orbitals and
the filled ligand in-phase and out-of-phase orbitals are the HOMO-3 and HOMO-4.
84
Figure 4.5 Interactions between  orbital on the dimetal unit and the filled ligand 
obritals as well as the ligand * orbitals. Modified from reference 95.
It can be seen in Figures 4.4 and 4.5 that the ligand in-phase  and * orbitals are
not of the proper symmetry to interact with metal centered molecular orbitals. However,
the out-of-phase  and * orbitals of the ligand can interact with the  orbital of the
metal. The ligand filled  orbitals can donate electron density to the metal center,
destabilizing it, while the ligand * orbital can accept electron density from the metal
center via backbonding, stabilizing the  orbital and to a greater degree destabilizing the
ligand * orbital. The energy separation between the in-phase and out-of-phase *
orbitals gives a qualitative indication of the amount of communication occurring through
the dimetal center.82 It can be seen that on raising the energy of the MM HOMO on
going from molybdenum to tungsten while keeping the ligand identity the same, the
85
splitting between the in-phase and out-of-phase * orbitals increases due to the greater
overlap between the MM and ligand * orbitals. For 1a E = 0.32 eV which increases
to 0.44 eV for 1b. Likewise, the E of 2a is 0.15 eV, while for 2b it is 0.23 eV. It is also
interesting to note that when comparing complexes of the same metal but different
ligands (i.e. 1a v. 2a and 1b v. 2b), the anthracenylethynylcarboxylate complexes show a
smaller energy splitting between the in-phase and out-of-phase * orbitals as well as a
smaller stabilization of the delta HOMO compared to the tolyl analogues. This can be
explained by considering the filled ligand in-phase and out-of-phase  orbitals, which are
the HOMO-1 and HOMO-2 in 1a, 2a, and 2b and the HOMO-3 and HOMO-4 in 1b
(Figure 4.3). The ligand  orbitals of the anthracenyl complexes are ~ 1.0 eV closer in
energy to the MM HOMO, allowing for greater mixing. It can be seen in Figure 4.3 that
as the energy between the MM HOMO and the filled ligand  orbitals decreases (in the
order 1b > 1a > 2b > 2a) this interaction becomes stronger, leading to a greater splitting
of the ligand filled in-phase and out-of-phase orbitals (1b = 0.10 eV < 1a, 2b = 0.12 eV <
2a = 0.16 eV).
The balance between these donating and backbonding accepting
properties of the  and * orbitals explains the trend seen in the splitting of the *
orbitals, where as the metal interaction with the filled orbitals becomes weaker in the
order 2a > 2b > 1a > 1b, the backbonding interaction becomes stronger and the *
splitting increases in the order 2a < 2b < 1a < 1b.
4.5
Electrochemical Studies
In all cases the complexes show a one electron reversible oxidation wave
attributed to the removal of an electron from the M2  base HOMO, which occurs at ca.
86
0.22 V versus FeCp20/+ for the molybdenum complexes and at ca. - 0.36 V for the
tungsten complexes. The ease of oxidation of the tungsten complexes tracks well with
the calculated energy of the HOMO orbitals which occur at ~ 0.5 eV higher energy
versus molybdenum analogs. All complexes show multiple reduction waves, however
only the first one electron reduction wave is reversible or quasireversible.
This first
reduction potential is listed along with the oxidation potentials in Table 4.2.
The
anthracenyl complexes are ~ 0.6 V easier to reduce compared to the tolyl complexes due
to the greater conjugation of the anthracenyl ligand. This trend in reduction potentials
matched well with the calculated trend (see Figure 4.3 and Table 4.2).
Table 4.2 Oxidation and reduction potentials of complexes 1a, 2a, 1b,
and 2b in 0.1M Bu4NPF6/THF solution versus internal standard FeCp20/+.
4.6
Electronic Absorption
The electronic absorption spectra of the four complexes in THF are shown in
Figure 4.6. The assignments of the types of transitions seen experimentally were guided
by time-dependent density functional theory (TD-DFT) calculations which are shown in
Figure 4.7, as well as listed in Table 4.3. In all cases the lowest energy transition is a
87
metal to ligand charge transfer (MLCT) absorption from the M2  HOMO to the
arylethynyl carboxylate in-phase * LUMO, with max ~ 439 nm (1a), 520 nm (2a), 616
nm (1b), and 762 nm (2b). The max of the MLCT band shifts to lower energy as the 
conjugation of the ligand is increased from tolyl to anthracenyl and as the metal is altered
from molybdenum to tungsten. The intensity of this transition more than doubles on
going from molybdenum (1a  ~ 12,700 M-1cm-1) to tungsten (1b  ~ 30,500 M-1cm-1) as
the orbital overlap increases due to the higher energy tungsten orbital. In the higher
energy region of the electronic absorption spectrum, the arylethynylcarboxylate ligand * absorptions are observed at ~ 290 nm (1a and 2b) and ~ 390 nm (2a and 2b). These
transtitions are supported in the TD-DFT calculations (see Table 4.1) for 1a (calculated at
284 nm), 2a (calculated at 426 nm), 1b (calculated at 297 nm), and 2b (calculated at 443
nm). In the case of 1b and 2b the calculated MLCT transition from the W2  (HOMO) to
the formate carboxylate liands occurs at 344 nm and 349 nm, respectively. Typically
TD-DFT calculations on complexes of this type reflect the observed trends in absorption
energies but overestimate energies due to their inability to account for spin-orbit and
solvation effects. Experimentally this transition is observed as a weak band in 1b at ~
400 nm and is obscured by the ligand -* transition in 2b.
88
Normalized Absorbance / a.u.
2.5
2.0
1.5
1.0
0.5
0.0
200
300
400
500
600
700
800
900
Wavelength / nm
Figure 4.6 Absorption spectra of 1a (orange), 2a (red), 1b (blue), and 2b (green) in THF.
89
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
400
500
600
700
1.4
1.2
1.2
1.0
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0.0
200
300
400
Wavelength / nm
1.0
1.0
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
500
600
700
Calculated Oscillator Strength
1.2
400
600
0.0
800
700
1.4
Normalized Absorbance / a.u.
Calculated Oscillator Strength
90
1.2
1b
300
500
Wavelength / nm
1.4
0.0
200
1.4
2a
0.0
800
1.2
2b
1.5
1.0
0.8
1.0
0.6
0.4
0.5
0.2
0.0
200
Wavelength / nm
2.0
300
400
500
600
700
800
Normalized Absorbance / a.u.
300
0.0
800
1.6
Normalized Absorbance / a.u.
1.0
Calculated Oscillator Strength
1a
1.0
0.0
200
1.6
1.2
Normalized Absorbance / a.u.
Calculated Oscillator Strength
1.2
0.0
900
Wavelength / nm
Figure 4.7 Experimental normalized absorption spectra in THF of 1a (orange), 2a (red), 1b (blue), and 2b (green) plotted with the
time-dependent calculated transitions of in the gas phase.
90
Table 4.3 Orbital contributions of transitions of singlet ground state of (1a)
Mo2(O2CH)2(O2CC≡CTolyl)2, (2a) Mo2(O2CH)2(O2CC≡CAnthryl)2,
(1b) W2(O2CH)2(O2CC≡CTolyl)2, (2b) W2(O2CH)2(O2CC≡CAnthryl)2.
The TD-DFT calculations lend support to the assignment of the MLCT absorption
bands, as does the solvent dependence. Charge transfer transitions are known to exhibit
strong solvatochromism, a property that is observed in all four complexes.96 Figure 4.8
shows complexes 1b and 2b absorptions in chloroform, dichloromethane, benzene, THF,
and DMSO. The solvent dependence of all four complexes are given in Table 4.5.
91
1.4
Normalized Absorbance / a.u.
Normalized Absorbance / a.u.
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
400
450
500
550
600
650
700
750
1.2
1.0
0.8
0.6
0.4
0.2
0.0
400
500
600
700
800
900
1000
Wavelength / nm
Wavelength / nm
Figure 4.8 Normalized room temperature absorbance of (Left) 1b and (Right) 2b.
Chloroform (purple), dichloromethane (blue), benzene (green), THF (black), and DMSO
(red).
The red shift of the MLCT band tracks well with the increasing dielectric constant
for the non-coordinating solvents with the exception of benzene.
The trend in
coordinating solvents can be explained by considering that THF has been shown to
coordinate axially in single crystals of these complexes.16 As the donating ability of the
solvent increases from THF90 to DMSO91 the positive charge formed on the metal center
in the photoexcited state is better stabilized.92
4.7
Temperature Dependence of Absorbance
When a bis-bis complex is excited from the ground state to the 1MLCT state it can
be
thought
of
as
an
excited
state
mixed
valence
complex
(ESMV).95
While the hole is localized on the M2 center, the electron is in a ligand * orbital where it
may be delocalized over both ligands or localized on one. Figure 4.8 shows a schematic
representation of the potential energy surfaces of the ground and excited states in a
weakly coupled excited state mixed valence system (Class II in the Robin and Day
scheme)97, a system on the Class II/III border, and a completely delocalized Class III
92
system. In the most localized case shown, Class II, the offset in the nuclear configuration
between the ground and excited state is most pronounced and two minima can be seen
representing the change as the charge is localized on one ligand (La) versus the other (Lb).
As the coupling of the ligands through the metal center increases, the barrier to electron
transfer decreases, seen in the center of Figure 4.8, and the ESMV is said to be on the
Class II/III border. The completely delocalized Class III system is shown in the rightmost panel of Figure 4.8, where the nuclear configuration changes are the smallest and
the excited state potential energy well is almost directly nested above the ground state.
Figure 4.9 Potential energy surfaces representing the ground state (S0) and mixed
valence excited state (S1) in a weakly coupled Class II system (left), a system on the
Class II/III border (center), and in a completely delocalized Class III system (right).
Modified from ref 86
93
The vibronic features of the MLCT absorption band can be indicative of the
degree of coupling in the bis-bis complexes. In a strongly coupled ESMV complex, the
offset in the nuclear configuration between the ground and excited state is small, such
that the first vibronic feature ( = 0) would be expected to be the most intense (Figure
4.9, right). However, in complexes where the coupling is weaker, greater offset between
ground state and excited state nuclear coordinates occurs, and higher energy vibronic
features ( > 0) would be expected to be more intense.87
The low temperature absorption spectra of the 1a and 1b (top) and 2a and 2b are
plotted in Figure 4.10. At room temperature the MLCT bands (Figure 4.6) are broad and
relatively featureless suggesting a broad Boltzmann distribution of rotamers in
solution.86,52 As the temperature is lowered to 100 K, a red shift is observed in the
MLCT band and the vibronic features sharpen noticeably. The changes seen with the
lowering of the temperature can be understood in terms of geometries of the molecules in
solution. Although the planar C2 (1a, 1b) or D2h (2a, 2b) geometry represents an energy
minimum, thermal energy is sufficient to allow deviations from this structure.87 An
estimate of the relative preference for the planar geometry that maximizes M2  to L *
backbonding can be gleaned from the shift in energy of the max on going from room to
low temperature, where a smaller shift indicates a greater degree of coupling. As
coupling in the molecule increases the barrier to rotation at room temperature should
increase as the preference to maximize M2  to L * overlap increases. This is seen
experimentally as a greater percentage of molecules in the planar geometry even at room
temperature, which decrease the amount of change in the energy maxima of the room and
low temperature spectra. In the case of 1a, 1b, 2a, and 2b, the molybdenum complexes
94
exhibit a greater shift in max compared to the tungsten complexes, indicative of greater
coupling in the tungsten complexes (See Table 4.4). It can also be seen that in the
tungsten complexes (1b and 2b) at ~ 100 K,  = 0 is the most intense feature while in
the molybdenum complexes (1a and 2a) this is not the case. This difference indicates a
smaller offset of the ground and excited state potential energy surfaces and reflects the
greater coupling (see Figure 4.8) in tungsten complexes due to the better orbital energy
match between the W2  orbital and ligand * orbitals.
95
Absorbance / a.u.
0.8
0.6
0.4
0.2
0.0
27000
24000
21000
18000
15000
12000
-1
Energy / cm
1.0
Absorbance / a.u.
0.8
0.6
0.4
0.2
0.0
26000
24000
22000
20000
18000
16000
14000
12000
Energy / cm-1
Figure 4.10 (Top) Room temperature (dashed line) and low temperature absorption
(100K, solid line) of 1a (orange) and 1b (blue) in 2-MeTHF. (Bottom) Room temperature
(dashed line) and low temperature absorption (100K, solid line) of 2a (red) and 2b
(green) in 2-MeTHF.
96
4.8
Emission
When excited into the MLCT absorption band these molecules exhibit
luminescence. All four complexes exhibit fluorescence from the 1MLCT state as shown
in Figures 4.11 and 4.12, with maxima at 77K in 2-MeTHF at 564 nm (1a), 648 nm (2a),
668 nm (1b), and ~ 820 nm (2b). The molybdenum complexes show a second emission,
phosphorescence, from a lower lying triplet excited state with max = 1055 nm in 2MeTHF at 77K. The spacing of the vibronic features are ~ 400 cm-1 (See Table 4.2)
similar to the ground state MoMo stretching frequency. These findings, along with
previously observed ligand and solvent independence of the emission energy, allows the
assignment of this emission as arising from the 3MM* excited state.16,52 Complex 1b
also shows a second emission, max = 875 nm, while no further emissive states are
observed for 2b.
97
Figure 4.11 Low temperature absorption (100K, dashed line) and emission spectra (77K,
solid line) of 1a (orange) and 1b (blue) in 2-MeTHF.
Figure 4.12 Low temperature absorption (100K, dashed line) and emission spectra (77K,
solid line) of at 2a (red) and 2b (green) in 2-MeTHF.
98
Table 4.3 Room temperature and low temperature absorption and emission data of 1a, 2a, 1b, and 2b in 2-MeTHF.
99
99
4.9
Solvent Dependence of Emission
The solvent dependence of the emission of the tungsten complexes, 1b and 2b,
are of importance due to the fact that their triplet excited states are not as well understood
as molybdenum tetracarboxylate complexes where the triplet is known to almost always
be MM*.16,52 It is believed that these tungsten quadruply bonded bis-bis complexes
could have a triplet state that is MLCT in nature. A solvent dependence of the emissive
state would provide evidence to support a 1MLCT state.14,96 As can be seen in Figure
4.13 and Table 4.4, the fluorescence of these complexes show solvent dependence, as
expected for an MLCT state. The energy of the emission seems to be fairly independent
of the influence of non-coordinating solvents, as seen for complex 1b in Figure 4.13,
where the emission maxima in C6H6, CHCl3, and CH2Cl2 are at ~ 630 nm in all solvents.
However, a shift in max is seen in coordinating solvents, where 1b in THF exhibits a
fluorescence max ~ 674 nm and ~ 702 nm in DMSO. In the case of 2b, the fluorescence
max in most solvents is hard to determine precisely due to instrument detection
limitations; the max appears to fall in the area between the visible and NIR detector (~
800-830 nm). Only a tail of emission is detected in the NIR for solvents other than
DMSO, however, in DMSO a clear max is observed at ~ 980 nm, indicating a solvent
dependence in coordinating solvents of the emissive 1MLCT state.
100
Normalized Intensity / a.u.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
20000
18000
16000
14000
12000
10000
8000
Energy / cm-1
Figure 4.13 Normalize emission of 1b in chloroform (purple), dichloromethane (blue,
RT), benzene (green, RT), THF (black, RT), 2-MeTHF (black dashed, 77K), and DMSO
(red, RT).
Unfortunately, the solvent dependence of the triplet state in complexes 1b and 2b
is more elusive. Complex 1b does not show a clear solvent dependence of the NIR
emission in 2-MeTHF and DMSO, and 2b does not exhibit emission from the triplet
state. In the case of 1b, the lack of apparent solvent dependence may be due to the
weakness of the emission at room temperature combined with the fact that it occurs near
the edge of the detection limit of the NIR instrument.
101
Table 4.4 Solvent dependence of absorption and emission of 1a, 2a, 1b, 2b.
102
102
4.10 Transient Absorption
The excited states of complexes 1a, 2a, 1b, and 2b have been probed with
femtosecond (fs-TA) and nanosecond (ns-TA) transient absorption. The broadband fsTA of 1a is not shown due to the weak signal observed, however, a lifetime for the
1
MLCT state was obtained from time-resolved infrared experiments (Figure B.2). When
excited with monochromatic light into the MLCT absorption band (ex 2a = 514nm),
complex 2a displays excited state absorption in the visible region attributed to the
1
MLCT state (Figure 4.14).
The 1MLCT states of 1a and 2a undergo intersystem
crossing (ISC) to long lived triplet states in ~5.0 ps (1a) and ~10.5 ps (2a). The triplet
states of 1a and 2a were probed with nanosecond transient absorption (Figure 4.15-4.16),
where they were observed to decay in ~ 103 s and ~83 s, respectively. As previously
mentioned, based on solvent studies and vibronic features, the triplet state in the
molybdenum complexes is identified as 3MM*; the observed lifetimes on the s
timescale are consistent with the triplet lifetimes of similar complexes.16,52
Figure 4.14 Femtosecond transient absorption of 2a in THF, exc = 514 nm.
104
Figure 4.15 Nanosecond transient absorption of 2a in THF, exc = 532 nm.
105
Figure 4.16 Nanosecond transient absorption of 1a in THF, exc = 355 nm.
106
Complexes 1b and 2b were explored with fs-TA (ex 1b = 514nm, ex 2b = 675
nm), and the broadband spectra are shown in Figures 4.17 and 4.18. In the case of 1b
there are absorption features at ~380 nm and ~670 nm and a bleach at ~600 nm attributed
to the absorption of the 1MLCT excited state and to the depletion of the ground state,
respectively. The absorption at ~380 nm decays in less than 1 ps to a longer lived triplet
state that remains through the duration of the experiment ( > 3 ns). However, the weak
absorption at ~670 nm is made up of two decay components detectable on the
femtosecond timescale, one which matches the decay at 380 nm ( ~1 ps) and a second
longer lived decay with  = 5 ps, which is attributed to vibrational cooling in the triplet
state. In the case of 2b there is a broad absorption in the 1MLCT state from ~475-625
nm and bleaches at ~ 410 nm and ~650 which match well with the ground state ligand * absorption and MLCT absorption, respectively. The absorption bands decay with a
single lifetime of  = 20 ps to a long lived triplet state that remains through the duration
of the experiment. The ISC rate of the anthracenyl complexes (2a and 2b) are slower
than the ISC rates of the tolyl counterparts; similar ISC trends have been observed in
related Mo2(TiPB)2(O2C-(C4H3S)n)2 complexes where n = 1, 2, or 3, [Mo2(O2CtBu)3]2-L
complexes
where
dithienylthiophenedicarboxylate,
oligomers.52,98,99
L
=
thienylthiophenedicarboxylate
and
platinum(II)
containing
or
phenyl-ethynyl
In these aforementioned cases the ISC rate decreases with the
increasing number of thiophene rings or ethnyl phenyl groups; this is proposed to be due
to decreased spin-orbit coupling.
This decreased spin-orbit coupling occurs as a
consequence of the electron in the excited state being more localized on the conjugated
ligand and spatially farther from the metal center.99
107
It is interesting to note in the case
of 2b that the absorption observed at long times in the fs-TA experiment (attributed to the
triplet excited state) matches well with the absorption of the radical anion of anthracene,
lending support to the assignment of the triplet state in this complex as 3MLCT.100 Both
1b and 2b were explored with nanosecond transient absorption, where weak signals were
detected (Figure 4.19), however, due to instrument limitations and the very short lifetime
of these complexes, the kinetics of the triplet state could not be accurately determined
and are therefore estimated as 3-10 ns. The very short triplet lifetimes in 1b and 2b,
though only estimates, give a very good indication of the nature of the triplet state. The
3
MM* state has been observed in W2(TiPB)4, with a relatively long lifetime of 1 s.16
It is also know that molybdenum tetracarboxylates with 3MM* excited states display
similar triplet lifetimes relatively independent of the type of ligand on the complex (3090 s).16,52,20 Therefore, it is expected that all tungsten carboxylates with 3MM*
excited states should have triplet lifetimes close to 1 s. Complexes 1b and 2b, display
triplet lifetimes two orders of magnitude shorter than that of W2(TiPB)4, which again
supports the assignment of an excited state other than 3MM*, possibly 3MLCT. A
summary of these results are given in the Jablonski diagram in Figure 4.20.
108
Figure 4.17 Femtosecond transient absorption of 1b in THF, exc = 514 nm.
109
Figure 4.18 Femtosecond transient absorption of 2b in THF, exc = 675 nm.
110
Figure 4.19 Nanosecond transient absorption of 1b and 2b in THF, exc = 532 nm.
111
Figure 4.20 Jablonski diagram summarizing the photophysical properties of 1a (orange),
2a (red), 1b (blue) and 2b (green).
4.11 Time Resolved Infrared Spectroscopy
The insertion of an acetylene unit into the ligand of these complexes is useful not
only for relieving steric hindrance between the aryl and carboxylate unit, but also because
it can act as an IR marker which can be tracked in the ground and excited states of the
complexes. The tungsten complexes, 1b and 2b, were explored with time-resolved
infrared spectroscopy (TRIR) to help in the determination of the nature of the singlet and
triplet excited states. In this pump-probe experiment the molecules are excited with
monochromatic light to populate the 1MCLT excited state and then they are probed with
IR light. In the ground state the C≡C asymmetric stretch occurs at 2220 cm-1 in 1b and
2185 cm-1 (shoulder at ~2208 cm-1) in 2b. The appearance of two (C≡C) bands in
complexes 2b and 2a (See Figure B.1) is not completely understood, however, one
112
possible explanation is that a mixture of isomers exist in these samples. In a trans
substituted highly symmetric dimetal bis-bis complex a single (C≡C) would be expected
due to the similar environment of both acetylene containing ligands as has been observed
previously
in
trans-M2(O2CMe)2((N[iPr])2CC≡CC6H5)2
complexes95
and
trans
substituted platinum complexes, [Pt((nBu)3P)2(ethynylbenzene)2] and [Pt((nBu)3P)2(1,4diethynylbenzene)2],101 and is also observed here in complexes 1a and 1b for which the
trans conformation has been confirmed by a crystal structure of 1a. However, in the cis
substituted complex Pt(dnpebpy)(C≡Cnap)2, where dnpebpy = 4,4'-dineopentylester-2,2'bipyridine and CCnap = 1-ethynylnaphthalene, two (C≡C) bands are observed in the
ground state.102 Due to the bulky nature of the TiPB ligands, bis-bis complexes of Mo2
and W2 carboxylates usually substitute in a trans manner, however, the growth of single
crystals of complexes 2a and 2b for X-ray crystal diffraction is currently underway to
confirm the substitution of these complexes.
The femtosecond TRIR spectra of 1b and 2b are shown in Figure 4.21. Upon
excitation, 1b shows a peak at 1975 cm-1 attributed to the C≡C stretching frequency in the
1
MLCT state. This band decays with = 0.69 ps to a band at 2000 cm-1 which remains
through the duration of the experiment. The decay of the 1MLCT state is consistent with
results observed in the fs-TA experiments. The band at 2000 cm-1 is attributed to the
triplet excited state. The fact that the triplet excited state exhibits a ligand stretching
frequency indicates that it is MLCT in nature95; this allows the assignment of 3MLCT for
T1 in 1b.
The results observed in 2b are less straightforward. An initial peak is formed at
2144 cm-1, which increases in intensity and blue shifts to 2150 cm-1 in less than 1 ps,
113
attributed to vibrational relaxation103. The peak at 2150 cm-1, attributed to the C≡C
stretch in the 1MLCT state, then decays with  = 19 ps, consistent with the lifetime
observed in the fs-TA experiment. It is interesting to note though that no C≡C stretching
frequency appears to remain in the triplet state of 2b, unless it is very weak. This is
contrary to what would be expected for a 3MLCT excited state.95
In the 1MLCT state the C≡C stretching frequency of both complexes is shifted to
lower energy relative to their ground state (C≡C). This indicates that an electron has
been placed in an antibonding orbital involving the C≡C, weakening the bond between
the two carbons.104,101 It can be seen that the shift is much greater for 1b (E = 245 cm-1)
versus 2b (E = 33 cm-1), showing that the C≡C bond is weakened more in the tolyl
complex compared to the anthracenyl complex. This indicates that the electron density is
more concentrated on the C≡C unit95 in the 1MLCT state of 1b compared to 2b, perhaps
due to the electron density being spread out onto the anthracene unit.
These data
correlate well with the longer ISC observed in the fs-TA for 2b, discussed in the previous
section, attributed to an excited state that is more localized on the aryl portion of the
ligand and spatially farther from the metal center. The disappearance of the C≡C signal
completely in the triplet state of 2b might also be explained by similar logic. If in the
triplet excited state the electron density in 2b is even less concentrated on the ethynyl unit
and instead localized on the anthracenyl section of the ligand, the ethynyl stretching
frequency would be relatively unchanged compared to the ground state making it
undetectable in the TRIR spectrum.
Time resolved IR spectroscopy can also be used as a means to explore the
charge delocalization in the excited state of these complexes. As explained in Section 4.7
114
and depicted in Figure 4.9, when these complexes are excited into their 1MLCT excited
state, they can be thought of as ESMV complexes, where the electron is localized on one
ligand or delocalized over both, depending on the amount of coupling through the metal
center.95 The amount of delocalization in the excited state can be estimated based on two
factors. First, in a more localized state two distinct C≡C frequencies would be observed,
compared to a completely delocalized state where a single C≡C signal is expected.
Secondly, the shift in the (C≡C) in the excited state compared to the ground state can be
compared to the calculated shift in the (C≡C) on going from the neutral complex to the
anion.95 It has been observed that in a delocalized system the shift matches well with the
calculated shift, where in a more localized system the shift is greater due to the
localization of the charge on only one ligand. In these tungsten carboxylate complexes
(1b, 2b) it can be seen that is both cases one strong band is observed which is attributed
to the (C≡C) in the excited state, which indicates a delocalized system. However, there
is also the possibility that these molecules enter a localized excited state but that the C≡C
stretch on the neutral ligand occurs at the same frequency as the ground state and
therefore two distinct peaks in the excited state are not observed. In comparing the two
complexes with their calculated shifts (Table 4.6), it can be seen that the trend in the
shifts where E 1b > E 2b matches well with the calculated trend. However, the shift
observed is much greater in 1b (E = 245 cm-1) and smaller in 2b (E = 33 cm-1)
compared to the calculated shifts, indicating a more delocalized excited state in 2b versus
a more localized state in 1b. However, 1MLCT states localized on one ligand where the
E differences observed are due soley to the greater conjugation of the anthracenyl unit
versus the tolyl unit cannot be ruled out at this time.
115
Figure 4.21 fs-TRIR of 1b (top) and 2b (bottom).
116
Table 4.5 Summary of the excited state dynamics and ground and excited state IR
frequencies.
4.12 Conclusions
Four new quadruply bonded dimetal complexes were synthesized which include
steric relieving C≡C units. The band gaps of the complexes are tunable with the variation
of the metal centers and ligands, allowing for absorption throughout the entire visible and
near-IR region.
All the complexes exhibit emissive singlet excited states and the
molybdenum complexes exhibit long lived (s) emissive MM* excites states. The
tungsten complexes also exhibit relaxation from their singlet excited states to relatively
longer lived (ns) triplet excited states, observed by transient absorption spectroscopy and
TRIR spectroscopy.
Based on the short triplet lifetimes as well as the transient
absorption profile of 2b, which shows similarities to the radical anion absorption, and the
C≡C stretching frequency observed in triplet state of 1b, the tungsten complexes are
believed to have triplet excited states that are MLCT in nature.
117
4.13 Experimental Section
4.13.1 X-Ray Crystallography
Crystallographic data for Mo2(TiPB)2(O2CC2C6H4CH3)2∙4THF were collected at
150K using an Oxford Cryosystems Cryostream Cooler. The data collection strategy was
set up to measure a hemisphere of reciprocal space with a redundancy factor of 3.0,
which means that 90% of the reflections were measured at least 3.0 times.
combination of phi and omega scans with a frame width of 1.0o was used.
A
Data
integration was done with Denzo105, and scaling and merging of data was done with
Scalepack105.
Merging the data and averaging the symmetry equivalent reflections
resulted in a Rint value of 0.043.
The structure was solved by the Patterson method in SHELXS-97106 in space
group Pī. The Mo dimer contains an inversion center and a THF molecule is bonded to
each end of the dimer through a long Mo∙∙∙O interaction of 2.617(2) Å. There is also a
solvent molecule of THF present in the asymmetric unit. Both THF molecules contain
some disorder. In the THF molecule bonded to the Mo dimer, one carbon atom is
disordered over two sites. It is labeled as C (28A) and C (28B). For the THF solvent
molecule, the designated oxygen atom, O (6), acquired a large B value, along with the
carbon atoms in the molecule. Renaming this oxygen atom as a carbon atom did not
improve the model. There happened to be a residual peak near it which, based on
geometry, could be an alternate site for this atom. So it was relabeled as an oxygen atom
disordered over two sites: O (6A) and O (6B). All disordered atoms were refined
isotropically. Full-matrix least-squares refinement based on F2 were performed in
SHELXL-97106, as incorporated in WinGX package107.
118
For the methyl groups, the hydrogen atoms were added at calculated positions
using a riding model with U(H) = 1.5 *Ueq (bonded carbon atom). The torsion angle,
which defines the orientation of the methyl group about the C-C bond, was refined. The
remaining hydrogen atoms were included in the model at calculated positions using a
riding model with U(H) = 1.2 *Ueq (attached atom). The final refinement cycle was
based on 7415 intensities and 376 variables and resulted in agreement factors of R1(F) =
0.052 and the R1(F) value is 0.037 for 6086 reflections. The final difference electron
density map contains maximum and minimum peak heights of 0.79 and -0.74 e/Å3.
Neutral atom scattering factors were used and include terms for anomalous dispersion.108
4.13.2 Materials and Methods
1
HNMR spectra were recorded on a 400MHz Bruker DPX Advanced400
spectrometer.
Samples were prepared in dry, degassed solvents in J. Young tubes.
Chemical shifts are referenced to the residual protio solvent peak.
Matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass
spectra were obtained on a Bruker Microflex mass spectrometer provided by a grant from
the Ohio BioProducts Innovation Center. The spectrometer was operated in a reflective,
positive ion mode. Dithranol was used as the matrix and prepared as a saturated solution
in THF. Electrospray ionization (ESI) was performed at the Ohio State Campus
Chemical Instrument Center Mass Spectrometry and Proteomics Facility with a
Micromass LCT. Microanalysis was performed by Atlantic Microlab Inc.
Cyclic (50-100 mV s-1) and differential pulse (36.36 mVs-1) voltammograms were
collected using a Princeton Applied Research (PAR) 173A potentiostat-galvanostat
equipped with a PAR 176 current-to-voltage converter. Electrochemical measurements
119
were performed under an inert atmosphere in a 0.1 M solution of nBu4NPF6 in THF inside
a single-compartment voltammetric cell equipped with a platinum working electrode, a
platinum wire auxiliary electrode, and a pseudo reference electrode consisting of a silver
wire in 0.1 M nBu4NPF6/THF separated from the bulk solution by a Vycor tip. The
potential values are referenced to the FeCp2/FeCp2+ couple.
All room temperature photophysical experiments were carried out on sample
solutions sealed in 1 cm x 1 cm quartz cuvettes sealed with Kontes taps. Electronic
absorption spectra at room temperature were recorded on a Hewlett-Packard diode array
spectrometer (HP8453). Low temperature absorption spectra were obtained using a
Perkin-Elmer Lambda 900 UV-vis NIR spectrometer from 2-MeTHF sample solutions.
Low temperature absorption spectra were obtained with a Specac variable temperature
cryostat employing a permanently sealed liquid IR cell with CaF2 windows.
Steady-state luminescence spectra were recorded on a SPEX Fluoromax-2
spectrofluorimeter in UVvisible region. Steady-state NIR-luminescence spectra were
collected on a home-built instrument utilizing a germanium detector. For detecting
emission in the NIR region, the samples were excited at 405 nm, 532 nm, and 785 nm. A
RG830 long pass filter was placed between the sample and the detector. Low
temperature emission experiments were carried out on 2-MeTHF sample solutions in J.
Young NMR tubes cooled with liquid N2 in a glass dewar.
In the femtosecond transient absorption experiments, the samples were excited at
514 or 675 nm with excitation power ~ 1 – 2 μJ at the sample. Using standard glove box
techniques, samples were prepared having an absorbance ~ 0.4 - 0.8 at the excitation
wavelength and contained in a 10.0 X 1.0 mm quartz cuvette (starna cells, inc.) that was
120
modified with a Kontes stopcock. The laser and detection systems that were used have
been described in detail previously.67 During the measurements, the samples were kept
in constant motion by manual movement of an XYZ stage in the vertical and horizontal
directions. In order ensure that no photodecomposition occurred during data collection,
absorption spectra were recorded before and after the transient absorption measurements.
The measurements were repeated five times at each of the pump-probe delay positions to
confirm data reproducibility throughout the experiment and the resulting spectra were
corrected for the chirp in the white-light super continuum. The kinetics were fit to a
single exponential decay of the form, S(t) = A*exp(-t/τ) + C, with amplitude, A, lifetime,
τ, and offset, C, using SigmaPlot 10.0. Error bars for the lifetimes are reported as the
standard error of the exponential fit.
Nanosecond transient absorption spectra were measured on a home-built
instrument, described in detail previously68, pumped by a frequency doubled (532 nm) or
tripled (355 nm) Spectra-Physics GCR-150 Nd:YAG laser (fwhm ~ 8ns, ~ 5 mJ per
pulse).
Ground state infrared spectra were obtained with a Perkin Elmer Spectrum GX.
Samples were sealed in a Perkin Elmer rectangular semi-demountable cell with a 0.1 mm
Teflon spacer between a 4 mm thick CaF2 back window and 2 mm thick CaF2 front
window. THF was the solvent and the concentration was such that the absorbance was ~
1.0 – 2.0 at the MLCT λmax. The spectra were baseline corrected and smoothed with the
instrument software and then the background THF spectrum was subtracted.
The laser system for the TRIR setup utilizes a Ti:Sapphire oscillator and
regenerative amplifier combination operating at 1 kHz that has been described in detail
121
previously.67 The fundamental laser beam is split to pump either an SFG or UV/vis OPA
to produce pump pulses tunable throughout the visible spectrum and a DFG OPA to
produce mid-IR pulses (2 to 10 μm). The IR beam is split into a probe and a reference
beam by a Ge beamsplitter. Each are focused onto the sample cell where only the probe
is overlapped with the pump beam. After the sample, the probe and reference beams are
directed to a grating spectrometer (Triax 320) and spectrally dispersed onto separate
HgCdTe array (32 elements) detectors cooled by liquid nitrogen. The pump and probe
pulses are synchronized by passing the pump pulse through a chopper operating at 500
Hz, allowing for measurement of the probe signal under pump on/off conditions.
Corresponding absorbance signal from the reference beam is subtracted to obtain the
overall signal. The TRIR setup has been described previously.109
Samples were sealed in a Perkin Elmer rectangular semi-demountable cell with a
0.1 mm Teflon spacer between a 4 mm thick CaF2 back window and 2 mm thick CaF2
front window in a glove box. THF was the solvent and the concentration was such that
the absorbance was ~ 1.0 – 2.0 at the MLCT λmax. During measurements, the static
sample cell was periodically translated manually using an XYZ stage.
Absorption
spectra were obtained before and after measurements to ensure that no photodecomposition had occurred. The spectra shown in Figure 4.20 consist of multiple
experiments covering different ranges of the IR probe light. Gaps in the spectra occur
where the probe wavelengths do not overlap between different experiments.
4.13.3 Computational Methods
The geometries of the model compounds were optimized in the gas-phase using
density functional theory (DFT) with the aid of the Gaussian03 suite of programs. The
122
B3LYP functional was used along with the SDD energy consistent pseudopotentials for
Mo and W, 6-31G* basis set for H, C, and O. Optimizations of the singlet ground states
were performed in C2 symmetry for M2(O2CH)2(O2C-C≡C-Tolyl)2 and D2h symmetry for
M2(O2CH)2(O2C-C≡C-Anthracenyl)2 and were confirmed to be minima on the potential
energy surface by frequency analysis. All GaussView plots are shown with isovalue 0.02.
4.13.4 Synthesis
p-Tolylacetylene was purchased from Acros Organics and dried over molecular
sieves. 9-Bromoanthracene (used as received) and trimethylsilylacetylene (dried over
molecular sieves) were purchased from Acros Organics.
purchased
from
Sigma
Aldrich
and
used
as
Copper (I) iodide was
received.
Trans-
dichlorobis(triphenylphosphine) palladium (II) was purchased from Strem Chemical and
used as received. 1-(9-Anthracenyl)-2,2-dibromoethene was prepared according to a
previously published procedure.94 Unless otherwise noted, all procedures were carried
out using standard air-sensitive techniques with dry, degassed solvents.
3-(4-Tolyl)propynoic acid. p-tolylacetylene (2.45 ml, 2.22 g, 0.0193 mol) was
diluted with 100 ml THF in a 250 ml Schlenk flask under argon. The reaction flask was
cooled to 0oC with an ice bath. 2.5 M n-butyl lithium hexanes solution (7.80 ml, 0.0195
mol) was added to the reaction flask dropwise. The reaction flask was allowed to warm
to room temperature and then the solution was stirred for one hour at room temperature.
Carbon dioxide was passed through a drying tube filled with anhydrous calcium sulfate
and bubbled through the reaction solution for 90 minutes. The reaction flask was then
opened to air and 200 ml 2% KOH (aq) solution was added. The aqueous reaction
mixture was extracted with diethyl ether until ether layer was clear (3 x 150 ml). HCl (1
123
M) was added to the aqueous solution and the product precipitated out of solution as a
white solid. Product was recrystallized from THF and hexanes. Yield: 2.128 g (69 %).
1
HNMR (DMSO-d6): H (400 MHz) 7.50 (d, 2H), 7.275 (d, 2H), 2.34 (s, 3H) ppm. ESI:
Found: 183.0 and 343.0. Single acid C10H8NaO2 requires 183.2 and hydrogen bonded
dimer C20H16NaO4 requires 343.3.
3-(9-Anthracenyl)propynoic acid. Method A. Synthesis modified from refs
110,111
. Trimethylamine (100ml) was added to 9-bromoanthracene (1.786g, 6.94 mmol),
copper iodide (0.078g, 0.410 mmol), and trans-dichlorobis(triphenylphosphine)
palladium
(II)
(0.1192g,
0.169mmol)
in
a
Schlenk
flask
under
argon.
Trimethylsilylacetylene (1.766ml, 1.227g, 12.50mmol) was added dropwise via syringe;
upon addition reaction mixture changed from yellow to dark brown.
Solution was
refluxed at 76oC for 20 hours. 9-trimethylsilylethynyl anthracene (orange) was purified
by column chromatography with hexanes as elutant. Yield: 0.7080 g (37 %).
9-Trimethylsilylethynyl anthracene (0.2037g, 0.742mmol) was dissolved in 100
ml degassed THF/MeOH (4:1) in a Schlenk flask under argon. A solution of potassium
hydroxide was added to the reaction flask via syringe (0.094g in 1.00ml water) and
reaction solution was allowed to stir at room temperature for 5.5 hours. Reaction solution
was opened to air and 25 ml of water were added. Product was extracted with 50 ml of
dichloromethane. Dichloromethane extraction was dried with magnesium sulfate solvent
was removed under vacuum.
9-ethynylanthracene (dark red semisolid) was carried
directly to next step.
9-Ethynylanthracene (0.1250g, 0.618 mmol) was dissolved in 150 ml dry
degassed THF under argon in a Schlenk flask. The reaction flask was cooled to -50-70oC
124
with a acetone/nitrogen(l) bath. 2.5 M n-butyl lithium in hexanes (0.245 ml, 0.618
mmol) was added dropwise via syringe. The red solution changed to blue and then to
dark brown upon addition of butyl lithium. The reaction mixture was stirred for 1.5 hrs in
bath and 1 hr at room temperature. Carbon dioxide was passed through a drying tube
filled with anhydrous calcium sulfate and bubbled through the reaction solution for 2 hrs.
The reaction flask was then opened to air and 100 ml 2% KOH (aq) solution was added.
The aqueous reaction mixture was extracted with diethyl ether until ether layer was clear
(3 x 100 ml).
HCl (1 M) was added to the aqueous solution and 3-(9-
anthracenyl)propiolic acid precipitated out of solution as a yellow solid. The solid was
recovered by suction filtration and washed with diethyl ether. Yield: 0.0200 g (11 %).
1
HNMR (DMSO-d6): H (250 MHz) 8.875 (s, 1H), 8.43 (d, 2H), 8.225 (d, 2H), 7.71 (dt,
4H) ppm.
Method B. 1-(9-Anthracenyl)-2,2-dibromoethene (1.569g, 4.33 mmol) was
dissolved in 150 ml THF in a Schlenk flask under argon. The reaction flask was cooled
to -50-70oC with a acetone/nitrogen(l) bath. 2.5 M n-butyl lithium in hexanes (3.82 ml,
9.54 mmol) was added dropwise via syringe. The red solution changed from orange to
green and then to brown upon addition of butyl lithium. The reaction mixture was stirred
for 2 hrs at room temperature. Carbon dioxide was passed through a drying tube filled
with anhydrous calcium sulfate and bubbled through the reaction solution for 90 minutes.
The reaction flask was then opened to air and 100 ml 2% KOH (aq) solution was added.
Aqueous reaction mixture was extracted with diethyl ether until the ether layer was clear
(3 x 100 ml).
HCl (1 M) was added to the aqueous solution and 3-(9-
anthracenyl)propynoic acid precipitated out of solution as a yellow solid. The solid was
125
recovered by suction filtration and washed with diethyl ether.
The solid was
recrystallized from THF and hexanes. Yield: 0.1560 g (15 %). 1HNMR (DMSO-d6): H
(400 MHz) 8.855 (s, 1H), 8.44 (d, 2H), 8.23 (d, 2H), 7.73 (dt, 4H) ppm.
Mo2(TiPB)2(O2CC≡C-p-Tolyl)2 (1a). 3-(4-Tolyl)propynoic acid (0.2001 g, 1.25
mmol) and Mo2(TiPB)4 (0.7384 g, 0.625 mmol) were dissolved in ca. 75ml of toluene in
a 200 ml centrifuge tube. An orange solution formed immediately upon addition of
solvent, which was allowed to stir for 4 days (56 hrs). The product (orange solid) was
isolated by centrifugation and supernatant was decanted. Product was then washed with
(3 x 20 ml) aliquots of toluene and 20 ml hexanes. Yield: 0.517 g (82%). Microanalysis:
found, C 62.27, H 6.20%. C52H60Mo2O8 requires C 62.15, H 6.02%. 1H-NMR (THF-d8):
(250 MHz)  7.60 (d, 2H); 7.28 (d, 2H); 7.10 (s, 2H); 3.25 (m, 2H); 2.95 (m, 1H); 2.40 (s,
3H); 1.35 (d, 12H); 1.28 (d, 6H). MALDI-TOF: found (1004.10, M+), calculated
(1004.91). UV-Vis max (THF/nm,  values in parentheses/M-1cm-1): 268 (37,500), 440
(12,700).
W2(TiPB)2(O2CC≡C-p-Tolyl)2 (1b). A slurry of 3-(4-tolyl)propynoic acid (0.058
g, 0.360 mmol) in toluene was added to a solution of W2(TiPB)4 (0.2573 g, 0.190 mmol)
in toluene. The solution turned from red to purple and was allowed to stir under argon
for 14 days at room temperature. The blue precipitate that formed was collected on a
sintered glass frit and washed with (2 x 10 ml) toluene and 5 ml hexanes, then dried
under vacuum to give a dark blue powder. Yield: 0.050 g (22%). Microanalysis: found,
C 51.89, H 4.89%. C52H60W2O8 requires C 52.90, H 5.12%. MALDI-TOF: found
(1181.9, M+), calculated (1180.33). UV-Vis max (THF/nm,  values in parentheses/M1
cm-1): 275 (34,500), 394 (10,800), 616 (30,500).
126
Mo2(TiPB)2(O2CC≡C-(9-Anthracenyl))2 (2a). Method A. 3-(9Anthracenyl)propynoic acid (prepared by Method A) ( (0.0100 g, 0.041 mmol) in toluene
was added to a reaction flask containing Mo2(TiPB)4 (0.0250 g, 0.021 mmol) in ca. 60 ml
toluene. The solution turned from yellow to red upon addition. The solution was
allowed to stir for 9 days. The red precipitate was collected on a sintered glass frit,
washed with (3 x 5 ml) toluene and 5 ml of hexanes, and then dried under vacuum. Yield:
0.020 g (40%) 1H-NMR (THF-d8): (400 MHz)  8.78 (d, 2H); 8.70 (s, 1H); 8.16 (d, 2H);
7.65 (dt, 4H); 7.10 (s, 2H), 3.40 (m, 2H); 2.95 (m, 1H); 1.38 (d, 12H); 1.26 (d, 6H).
MALDI-TOF: found (1178.6, M+), calculated (1178.27).
Method B. 3-(9-Anthracenyl)propynoic acid (prepared by Method B) ( (0.0560 g,
0.227 mmol) and Mo2(TiPB)4 (0.1343 g, 0.114 mmol) were combined in a centrifuge tube
with ca. 70 ml toluene. A red solution formed which was allowed to stir for 9 days. The
red precipitate was washed with (3 x 20 ml) toluene and 10 ml of hexanes, and then dried
under vacuum. Multiple species detected in NMR which were not able to be isolated.
Purification attempted: red solid washed with acetonitrile, ethanol, chloroform, toluene,
or diethyl ether with no change to NMR. Red solid heated to 110oC for 3 days under
vacuum to sublime out any impurities with no change to NMR. Red solid recrystallized
from THF and hexanes, with not change to NMR. 1H-NMR (THF-d8): (400 MHz)  8.78
(d, 2H); 8.70 (s, 1H); 8.61 (s, 0.35 H); 8.16 (d, 2H); 8.10 (d, 0.70 H); 7.65 (dt, 4H); 7.65
(m, ~1.4 H) 7.10 (s, 2H), 7.15 (s, 0.35 H); 3.40 (m, 3H); 2.90 (m, 2H); 1.38 (d, 12H);
1.26 (d, 6H); 1.38-1.26 (m, 6H) . MALDI-TOF: found (1178.6, M+), calculated
(1178.27).
127
W2(TiPB)2(O2CC≡C-(9-Anthracenyl))2 (2b). Method A. Combined 3-(9anthracenyl)propynoic acid (prepared by Method A) ( (0.0089 g, 0.036 mmol) and
W2(TiPB)4 (0.0250 g, 0.019 mmol) in ca. 50 ml toluene. The solution changed from red
to green within minutes and then was allowed to stir for 10 days at room temperature.
The green precipitate that formed was collected on a sintered glass frit and washed with
(3 x 1 ml) toluene and 1 ml hexanes. Yield: 0.010 g (40%). 1H-NMR (THF-d8): (400
MHz)  8.79 (d, 2H); 8.52 (s, 1H); 8.11 (d, 2H); 7.61 (m, 4H); 7.07 (s, 2H), 3.17 (m, 2H);
2.89 (m, 1H); 1.30 (d, 12H); 1.24 (d, 6H). MALDI-TOF: found (1355.2, M+), calculated
(1352.89).
Method B. 3-(9-anthracenyl)propynoic acid (prepared by Method B) ( (0.0455 g,
0.185 mmol) and W2(TiPB)4 (0.1254 g, 0.092 mmol) were combined in a centrifuge tube
with ca. 70 ml toluene. A green solution formed which was allowed to stir for 9 days.
The green precipitate was washed with (3 x 20 ml) toluene and 10 ml of hexanes, and
then dried under vacuum. Multiple species detected in NMR which were not able to be
isolated.
1
H-NMR (THF-d8): (400 MHz)  8.79 (d, 2H); 8.75 (d, 0.5H); 8.50 (s, 1H);
8.52 (s, 1H); 8.11 (d, 2H); 8.05 (m, 0.65H); 7.61 (m, 6H); 7.07 (s, 2H), 7.03 (s, 0.5H);
3.17 (m, 2H); 3.05 (m, 0.8H); 2.89 (m, 1.4H); 1.30 (d, 12H); 1.26-1.22 (m, 10H).
MALDI-TOF: found (1352.6, M+), calculated (1352.89).
128
CHAPTER 5
5. CONCLUSIONS
The photophysical properties of complexes containing multiply bonded dimetal
units at their core can be tuned with the alteration of metal atoms and bridging ligands.
This research compares the changes that occur in the photophysical properties as the
metals are altered from Mo, to W, to Re; as the bond order between the metal center
decreased from four to three, and as the ligand connectivity between the aromatic and
carboxylate portion of the ligand are altered as well as when the conjugation is altered.
In the second chapter complexes with rhenium dimetal centers are explored.
Re26+ complexes containing electron configurations similar to traditional Mo24+ and W24+
quadruply bonded complexes, 242, were explored as well as Re24+ complexes with
electron configurations of 242*2. The Re26+ complexes, due to the increased positive
charge on the metal centers, have a  orbital at is much lower in energy compared to
similar Mo24+ and W24+ complexes. The HOMO to LUMO transition therefore is not a
MLCT transition but rather occurs from a Re2 orbital to a Re2 * orbital calculated to
occur at 972 nm. The DFT calculations reveal that the orbital in the Re26+ complex is
the HOMO–1 and the Re2 to benzoate * transition occurs at 397 nm.
The * orbital energy of the triply bonded Re24+ complexes with configuration
242*2 at ~ -5.7 eV is closer to that of the Mo24+ orbital but has the wrong symmetry
129
to allow the HOMO to LUMO MLCT transition; note the calculated oscillator strength
for the HOMO-LUMO transition is 0.0004 in contrast to the M2  to ligand LUMO for M
= Mo or W where f ~ 0.8 to 1.1. The orbital in the Re24+ complexes is the HOMO–4
and the Re24+ to benzoate transition occurs at higher energy, 348 nm.
In terms of photovoltaic light harvesting, Re24+ and Re26+ cores hold less promise
in relation to the M24+ cores, where M = Mo2, MoW, or W2, which lead to 1MLCT
absorptions that traverse the solar emission spectrum.20,52,66
With regards to the
population of excited states that have MLCT character for charge injection, neither the
Re24+ complexes nor the Re26+ complex exhibit a MLCT state as their lowest energy
singlet excited state. The Re24+ complex clearly exhibits a 3* state as its lowest energy
triplet state, similar to Mo24+, and some W24+ complexes. Emission from the 3* state
has not been previously observed for a dirhenium tetracarboxylate complex.16
The
Re2(dppm)2(O2CC6H4NO2)2Cl2 complex exhibits a long lived excited state ( ~ ns) that
based on the appearance of the transient absorption, may have some ligand character.
Further studies need to be conducted to determine if efficient charge injection can occur
from this state.
The research in Chapter 3 clarifies how inserting an electron withdrawing ethynyl
moiety into the aromatic ligands of the bis-bis complexes affects the frontier orbitals by
stabilizing the filled metal orbitals and shifting the HOMO to lower energy with respect
to both the vinyl containing complexes and the previously published M2(TiPB)2(O2CTh)2
complexes. It can also be noted that insertion of the vinyl moiety causes the ligand based
reductions to occur
at ~0.4 V more positive potential compared to the
M2(TiPB)2(O2CTh)2 complexes, reflecting the greater conjugation which lowers the
130
LUMO * energy. This research also displays the difference in the nature of the W2 core
versus the Mo2 core and the greater degree of electronic communication that occurs in
complexes of the former. This control of orbital energetic and understanding of electron
delocalization will be useful for incorporating these bis-bis complexes into photovoltaic
devices with various acceptor complexes and electrodes.
In Chapter 4, four new quadruply bonded dimetal complexes were synthesized
which include steric relieving C≡C units. The band gaps of the complexes are tunable
with the variation of the metal centers and ligands, allowing for absorption throughout the
entire visible and near-IR region. All the complexes exhibit emissive singlet excited
states and the molybdenum complexes exhibit long lived (s) emissive MM* excites
states. The tungsten complexes also exhibit relaxation from their singlet excited states to
relatively longer lived (ns) triplet excited states, observed by transient absorption
spectroscopy and TRIR spectroscopy. Based on the short triplet lifetimes as well as the
transient
absorption
profile
of
W2(TiPB)2(O2CC≡CAnthracene)2,
which
shows
similarities to the radical anion absorption, and the C≡C stretching frequency observed in
the triplet state of W2(TiPB)2(O2CC≡CTolyl)2, the tungsten complexes are believed to
have triplet excited states that are MLCT in nature.
The work described here offers a better understanding of the electronic structure
of some multiply bonded metal complexes and how the photophysical properties can be
tuned. The ditungsten complexes with highly conjugated ligands offer low energy,
intense, absorption bands close to the near IR region which show promise for efficient
solar energy harvesting. The electrochemistry and the MLCT absorption profile at low
temperature in the ditungsten complexes reveal a degree of electron delocalization that
131
will be useful for charge transport when used as the active layer in metal-organic hybrid
solar cells. Finally, the confirmation of the lowest energy triplet state in two of the
ditungsten complexes as MLCT in nature is promising for charge separation and charge
injection in optoelectronic devices.
132
APPENDIX A
CRYSTALLOGRAPHIC DATA FOR Re2(dppm)2(O2CC6H4NO2)2Cl2·2 THF AND
Mo2(TiPB)2(O2CC2C6H4CH3)2∙4 THF
133
Table A.1 Crystallographic details for Re2(dppm)2(O2CC6H4NO2)2Cl2·2 THF
Molecular formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 29.12°
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole
C64 H52 Cl2 N2 O8 P4 Re2 + 2(THF)
1688.46
150(2) K
0.77490 Å
monoclinic
C2/c
a = 31.062(7) Å
b = 10.454(3) Å
c = 24.183(6) Å
= 124.225(3)°
6493(3) Å3
4
1.727 Mg/m3
4.769 mm-1
3352
0.08 x 0.03 x 0.01 mm3
3.97 to 29.12°
-38<=h<=38, -13<=k<=13, -30<=l<=30
34819
6692 [R(int) = 0.131]
99.5 %
Full-matrix least-squares on F2
6692 / 0 / 415
0.971
R1 = 0.0500, wR2 = 0.1002
R1 = 0.1040, wR2 = 0.1197
1.512 and -2.242 e/Å3
134
Table A.2 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters
(Å2x 103) for Re2(dppm)2(O2CC6H4NO2)2Cl2·2 THF. U(eq) is defined as one third of
the trace of the orthogonalized Uij tensor.
________________________________________________________________________
x
y
z
U(eq)
________________________________________________________________________
C(1)
9305(4)
9530(8)
2115(4)
29(2)
C(2)
8909(4)
10557(9)
1906(5)
35(2)
C(3)
8694(4)
10712(9)
2278(5)
37(2)
C(4)
8279(4)
11573(9)
2061(5)
44(2)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
8077(4)
8278(4)
8702(4)
10784(4)
11053(3)
11364(4)
11849(4)
11996(4)
11673(4)
11196(4)
12179(8)
12024(9)
11184(8)
5115(8)
6053(8)
5006(10)
5208(11)
6418(11)
7439(12)
7265(9)
1456(5)
1074(5)
1313(4)
2992(4)
2102(4)
2203(5)
2296(5)
2258(5)
2119(5)
2038(4)
37(2)
41(2)
32(2)
30(2)
28(2)
41(2)
46(3)
45(3)
48(2)
38(2)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
10213(3)
10179(4)
9991(4)
9837(4)
9871(4)
10052(4)
11063(3)
11159(4)
11361(4)
4371(8)
3158(9)
2108(8)
2257(10)
3464(9)
4487(9)
5414(8)
6038(9)
5370(9)
1610(4)
1823(5)
1393(5)
737(5)
512(5)
938(5)
4328(4)
4906(5)
5493(5)
29(2)
34(2)
37(2)
46(3)
42(2)
40(2)
30(2)
40(2)
48(3)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
11482(4)
11390(5)
11175(4)
11447(3)
11796(4)
12239(4)
12345(4)
4090(10)
3475(10)
4141(9)
7235(8)
6982(9)
7719(10)
8708(10)
5526(5)
4976(5)
4374(5)
3868(4)
3706(5)
3955(5)
4394(5)
45(3)
50(3)
38(2)
30(2)
35(2)
46(2)
44(3)
135
Table A.2 (continued)
C(31)
C(32)
Cl
N
O(1)
O(2)
O(3)
O(4)
12009(4)
11554(4)
10140(1)
7629(3)
9454(3)
9485(2)
7422(3)
7468(4)
8949(9)
8249(8)
8086(2)
13023(8)
8944(6)
9308(5)
13072(7)
13586(9)
4588(5)
4316(4)
4094(1)
1207(5)
2642(3)
1754(3)
1510(4)
686(4)
44(3)
37(2)
40(1)
45(2)
33(2)
30(1)
50(2)
75(3)
P(1)
10481(1)
5791(2)
2139(1)
26(1)
P(2)
10845(1)
6343(2)
3568(1)
27(1)
Re
10063(1)
7579(1)
3020(1)
24(1)
O(5)
11593(3)
-1538(8)
6482(4)
66(2)
C(33)
11037(4)
-1668(11)
6102(6)
53(3)
C(34)
10830(4)
-386(10)
5772(5)
46(3)
C(35)
11234(4)
71(10)
5661(5)
48(3)
C(36)
11696(4)
-797(11)
6097(6)
57(3)
________________________________________________________________________
136
Table A.3 Bond lengths [Å] and angles [°] for Re2(dppm)2(O2CC6H4NO2)2Cl2·2 THF.
_____________________________________________________
C(1)-O(1)
1.245(10)
C(1)-O(2)
1.296(10)
C(1)-C(2)
1.492(12)
C(2)-C(7)
1.365(12)
C(2)-C(3)
1.398(12)
C(3)-C(4)
1.409(13)
C(3)-H(3)
0.9500
C(4)-C(5)
1.380(13)
C(4)-H(4)
C(5)-C(6)
C(5)-N
C(6)-C(7)
C(6)-H(6)
C(7)-H(7)
C(8)-P(2)
C(8)-P(1)
C(8)-H(8A)
C(8)-H(8B)
0.9500
1.384(13)
1.462(12)
1.409(13)
0.9500
0.9500
1.824(9)
1.860(9)
0.9900
0.9900
C(9)-C(14)
C(9)-C(10)
C(9)-P(1)
C(10)-C(11)
C(10)-H(10)
C(11)-C(12)
C(11)-H(11)
C(12)-C(13)
C(12)-H(12)
1.380(12)
1.389(12)
1.848(9)
1.406(14)
0.9500
1.366(15)
0.9500
1.372(15)
0.9500
C(13)-C(14)
C(13)-H(13)
C(14)-H(14)
C(15)-C(16)
C(15)-C(20)
C(15)-P(1)
C(16)-C(17)
1.393(13)
0.9500
0.9500
1.395(12)
1.412(12)
1.826(8)
1.395(12)
137
Table A.3 (continued)
C(16)-H(16)
C(17)-C(18)
C(17)-H(17)
C(18)-C(19)
C(18)-H(18)
C(19)-C(20)
C(19)-H(19)
C(20)-H(20)
0.9500
1.383(13)
0.9500
1.402(14)
0.9500
1.367(13)
0.9500
0.9500
C(21)-C(26)
C(21)-C(22)
C(21)-P(2)
C(22)-C(23)
C(22)-H(22)
C(23)-C(24)
C(23)-H(23)
C(24)-C(25)
C(24)-H(24)
C(25)-C(26)
1.364(13)
1.413(12)
1.838(8)
1.378(12)
0.9500
1.381(14)
0.9500
1.356(14)
0.9500
1.399(12)
C(25)-H(25)
C(26)-H(26)
C(27)-C(28)
C(27)-C(32)
C(27)-P(2)
C(28)-C(29)
C(28)-H(28)
C(29)-C(30)
C(29)-H(29)
0.9500
0.9500
1.371(12)
1.414(12)
1.834(9)
1.386(13)
0.9500
1.383(14)
0.9500
C(30)-C(31)
C(30)-H(30)
C(31)-C(32)
C(31)-H(31)
C(32)-H(32)
Cl-Re
N-O(4)
1.386(14)
0.9500
1.385(13)
0.9500
0.9500
2.525(2)
1.216(10)
138
Table A.3 (continued)
N-O(3)
O(1)-Re
O(2)-Re#1
P(1)-Re#1
P(2)-Re
Re-O(2)#1
Re-Re#1
Re-P(1)#1
1.217(10)
2.121(6)
2.162(6)
2.400(2)
2.390(2)
2.162(6)
2.3208(9)
2.400(2)
O(5)-C(36)
O(5)-C(33)
C(33)-C(34)
C(33)-H(33A)
C(33)-H(33B)
C(34)-C(35)
C(34)-H(34A)
C(34)-H(34B)
C(35)-C(36)
C(35)-H(35A)
1.381(12)
1.434(13)
1.506(14)
0.9900
0.9900
1.503(14)
0.9900
0.9900
1.514(14)
0.9900
C(35)-H(35B)
C(36)-H(36A)
C(36)-H(36B)
0.9900
0.9900
0.9900
O(1)-C(1)-O(2)
O(1)-C(1)-C(2)
O(2)-C(1)-C(2)
C(7)-C(2)-C(3)
C(7)-C(2)-C(1)
123.3(8)
117.5(8)
119.2(7)
120.5(9)
120.8(8)
C(3)-C(2)-C(1)
C(2)-C(3)-C(4)
C(2)-C(3)-H(3)
C(4)-C(3)-H(3)
C(5)-C(4)-C(3)
C(5)-C(4)-H(4)
C(3)-C(4)-H(4)
117.9(8)
120.1(9)
119.9
119.9
117.6(9)
121.2
121.2
139
Table A.3 (continued)
C(4)-C(5)-C(6)
C(4)-C(5)-N
C(6)-C(5)-N
C(5)-C(6)-C(7)
C(5)-C(6)-H(6)
C(7)-C(6)-H(6)
C(2)-C(7)-C(6)
C(2)-C(7)-H(7)
123.2(9)
118.2(9)
118.6(8)
117.9(9)
121.0
121.0
120.5(8)
119.7
C(6)-C(7)-H(7)
P(2)-C(8)-P(1)
P(2)-C(8)-H(8A)
P(1)-C(8)-H(8A)
P(2)-C(8)-H(8B)
P(1)-C(8)-H(8B)
H(8A)-C(8)-H(8B)
C(14)-C(9)-C(10)
C(14)-C(9)-P(1)
C(10)-C(9)-P(1)
119.7
110.5(5)
109.6
109.6
109.6
109.6
108.1
120.5(8)
121.3(7)
117.9(7)
C(9)-C(10)-C(11)
C(9)-C(10)-H(10)
C(11)-C(10)-H(10)
C(12)-C(11)-C(10)
C(12)-C(11)-H(11)
C(10)-C(11)-H(11)
C(11)-C(12)-C(13)
C(11)-C(12)-H(12)
C(13)-C(12)-H(12)
119.1(9)
120.5
120.5
119.9(10)
120.1
120.1
120.6(9)
119.7
119.7
C(12)-C(13)-C(14)
C(12)-C(13)-H(13)
C(14)-C(13)-H(13)
C(9)-C(14)-C(13)
C(9)-C(14)-H(14)
C(13)-C(14)-H(14)
C(16)-C(15)-C(20)
120.5(10)
119.8
119.8
119.2(10)
120.4
120.4
116.9(8)
140
Table A.3 (continued)
C(16)-C(15)-P(1)
C(20)-C(15)-P(1)
C(15)-C(16)-C(17)
C(15)-C(16)-H(16)
C(17)-C(16)-H(16)
C(18)-C(17)-C(16)
C(18)-C(17)-H(17)
C(16)-C(17)-H(17)
125.5(7)
117.6(7)
121.8(8)
119.1
119.1
119.8(9)
120.1
120.1
C(17)-C(18)-C(19)
C(17)-C(18)-H(18)
C(19)-C(18)-H(18)
C(20)-C(19)-C(18)
C(20)-C(19)-H(19)
C(18)-C(19)-H(19)
C(19)-C(20)-C(15)
C(19)-C(20)-H(20)
C(15)-C(20)-H(20)
C(26)-C(21)-C(22)
119.6(9)
120.2
120.2
120.1(9)
120.0
120.0
122.0(9)
119.0
119.0
117.9(8)
C(26)-C(21)-P(2)
C(22)-C(21)-P(2)
C(23)-C(22)-C(21)
C(23)-C(22)-H(22)
C(21)-C(22)-H(22)
C(22)-C(23)-C(24)
C(22)-C(23)-H(23)
C(24)-C(23)-H(23)
C(25)-C(24)-C(23)
122.0(7)
119.9(7)
120.4(9)
119.8
119.8
120.1(9)
119.9
119.9
120.2(9)
C(25)-C(24)-H(24)
C(23)-C(24)-H(24)
C(24)-C(25)-C(26)
C(24)-C(25)-H(25)
C(26)-C(25)-H(25)
C(21)-C(26)-C(25)
C(21)-C(26)-H(26)
119.9
119.9
119.9(9)
120.0
120.0
121.4(9)
119.3
141
Table A.3 (continued)
C(25)-C(26)-H(26)
C(28)-C(27)-C(32)
C(28)-C(27)-P(2)
C(32)-C(27)-P(2)
C(27)-C(28)-C(29)
C(27)-C(28)-H(28)
C(29)-C(28)-H(28)
C(30)-C(29)-C(28)
119.3
118.6(8)
125.6(7)
115.7(7)
121.5(9)
119.3
119.3
119.8(9)
C(30)-C(29)-H(29)
C(28)-C(29)-H(29)
C(29)-C(30)-C(31)
C(29)-C(30)-H(30)
C(31)-C(30)-H(30)
C(32)-C(31)-C(30)
C(32)-C(31)-H(31)
C(30)-C(31)-H(31)
C(31)-C(32)-C(27)
C(31)-C(32)-H(32)
120.1
120.1
119.9(9)
120.1
120.1
120.2(9)
119.9
119.9
119.9(9)
120.0
C(27)-C(32)-H(32)
O(4)-N-O(3)
O(4)-N-C(5)
O(3)-N-C(5)
C(1)-O(1)-Re
C(1)-O(2)-Re#1
C(15)-P(1)-C(9)
C(15)-P(1)-C(8)
C(9)-P(1)-C(8)
120.0
123.9(9)
117.3(9)
118.8(8)
120.0(6)
116.4(5)
99.1(4)
102.4(4)
102.0(4)
C(15)-P(1)-Re#1
C(9)-P(1)-Re#1
C(8)-P(1)-Re#1
C(8)-P(2)-C(27)
C(8)-P(2)-C(21)
C(27)-P(2)-C(21)
C(8)-P(2)-Re
121.2(3)
119.1(3)
110.2(3)
107.7(4)
102.3(4)
98.7(4)
108.7(3)
142
Table A.3 (continued)
C(27)-P(2)-Re
C(21)-P(2)-Re
O(1)-Re-O(2)#1
O(1)-Re-Re#1
O(2)#1-Re-Re#1
O(1)-Re-P(2)
O(2)#1-Re-P(2)
Re#1-Re-P(2)
115.9(3)
121.9(3)
80.9(2)
88.11(16)
87.87(15)
169.93(17)
89.90(16)
95.69(5)
O(1)-Re-P(1)#1
O(2)#1-Re-P(1)#1
Re#1-Re-P(1)#1
P(2)-Re-P(1)#1
O(1)-Re-Cl
O(2)#1-Re-Cl
Re#1-Re-Cl
P(2)-Re-Cl
P(1)#1-Re-Cl
C(36)-O(5)-C(33)
94.50(18)
171.84(16)
98.77(5)
94.13(8)
81.30(16)
83.83(16)
167.44(5)
93.71(8)
88.82(8)
105.9(8)
O(5)-C(33)-C(34)
O(5)-C(33)-H(33A)
C(34)-C(33)-H(33A)
O(5)-C(33)-H(33B)
C(34)-C(33)-H(33B)
H(33A)-C(33)-H(33B)
C(35)-C(34)-C(33)
C(35)-C(34)-H(34A)
C(33)-C(34)-H(34A)
104.9(9)
110.8
110.8
110.8
110.8
108.8
103.0(8)
111.2
111.2
C(35)-C(34)-H(34B)
C(33)-C(34)-H(34B)
H(34A)-C(34)-H(34B)
C(34)-C(35)-C(36)
C(34)-C(35)-H(35A)
C(36)-C(35)-H(35A)
C(34)-C(35)-H(35B)
111.2
111.2
109.1
104.2(9)
110.9
110.9
110.9
143
Table A.3 (continued)
C(36)-C(35)-H(35B)
H(35A)-C(35)-H(35B)
O(5)-C(36)-C(35)
O(5)-C(36)-H(36A)
C(35)-C(36)-H(36A)
O(5)-C(36)-H(36B)
C(35)-C(36)-H(36B)
H(36A)-C(36)-H(36B)
110.9
108.9
108.5(9)
110.0
110.0
110.0
110.0
108.4
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 -x+2,y,-z+1/2
144
Table A.4 Anisotropic displacement parameters (Å2x 103) for
Re2(dppm)2(O2CC6H4NO2)2Cl2·2 THF. The anisotropic displacement factor exponent
takes the form: -22[ h2a*2U11 + ... + 2 h k a* b* U12 ]
________________________________________________________________________
U11
U22
U33
U23
U13
U12
________________________________________________________________________
C(1)
35(5)
22(4)
26(5)
3(4)
15(4)
8(4)
C(2)
43(6)
35(5)
34(5)
2(4)
26(5)
1(4)
C(3)
52(6)
38(5)
31(5)
2(4)
29(5)
7(5)
C(4)
50(7)
44(6)
45(6)
8(5)
30(5)
6(5)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
37(5)
50(6)
49(6)
37(6)
33(5)
35(6)
43(6)
33(6)
54(6)
39(5)
36(5)
37(5)
28(5)
25(4)
32(5)
59(6)
67(7)
75(8)
59(6)
50(6)
35(5)
45(6)
35(5)
32(5)
25(4)
36(5)
35(6)
37(6)
44(5)
31(5)
2(4)
9(4)
-3(4)
-1(4)
-2(4)
7(5)
9(5)
3(5)
-2(6)
-3(4)
19(4)
32(5)
33(5)
22(5)
20(4)
25(5)
27(5)
25(5)
35(5)
22(4)
3(4)
0(4)
-2(4)
-3(4)
0(4)
5(5)
21(5)
-2(5)
-11(7)
-4(4)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
33(5)
34(5)
41(6)
49(6)
55(7)
56(7)
29(5)
52(6)
73(8)
34(5)
38(5)
28(5)
48(7)
44(6)
41(5)
36(5)
40(5)
44(6)
26(5)
36(5)
43(6)
48(6)
42(6)
39(6)
28(5)
32(5)
24(5)
-9(4)
-2(4)
-4(4)
-18(5)
-10(5)
-3(4)
11(4)
8(4)
9(4)
19(4)
23(5)
25(5)
32(5)
36(5)
37(5)
17(4)
26(5)
26(6)
-2(4)
1(4)
0(4)
1(5)
-3(5)
0(5)
5(4)
12(5)
12(5)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
61(7)
80(8)
45(6)
28(4)
34(5)
41(5)
34(6)
46(6)
37(5)
46(6)
36(5)
40(5)
62(7)
40(6)
28(5)
43(6)
25(5)
18(4)
32(5)
41(5)
39(6)
16(4)
18(5)
4(4)
2(3)
3(4)
3(5)
5(4)
24(5)
41(6)
20(5)
8(3)
19(4)
26(5)
9(5)
8(5)
16(5)
5(5)
-3(4)
7(4)
0(5)
-6(4)
145
Table A.4 (continued)
C(31)
C(32)
Cl
N
O(1)
O(2)
O(3)
O(4)
48(6)
45(6)
50(2)
53(6)
45(4)
34(4)
45(4)
92(7)
40(6)
32(5)
44(1)
42(5)
32(3)
26(3)
53(4)
88(6)
28(5)
27(5)
29(1)
55(6)
33(4)
29(3)
55(5)
72(6)
-3(4)
-1(4)
-4(1)
9(4)
-7(3)
-2(3)
6(4)
44(5)
11(5)
17(5)
24(1)
40(5)
28(3)
17(3)
31(4)
61(6)
-4(5)
4(4)
9(1)
8(4)
2(3)
-2(3)
11(3)
42(5)
P(1)
35(1)
29(1)
24(1)
-2(1)
21(1)
-1(1)
P(2)
35(1)
26(1)
22(1)
0(1)
18(1)
1(1)
Re
31(1)
24(1)
21(1)
0(1)
18(1)
1(1)
O(5)
56(5)
97(6)
52(5)
27(5)
35(4)
11(5)
C(33)
44(7)
70(8)
53(7)
2(6)
31(6)
-1(6)
C(34)
49(7)
56(6)
40(6)
3(5)
30(5)
9(5)
C(35)
47(7)
52(6)
41(6)
1(5)
22(5)
0(5)
C(36)
51(7)
62(7)
64(8)
16(6)
37(6)
-3(6)
________________________________________________________________________
146
Table A.5 Calculated hydrogen coordinates ( x 104) and isotropic displacement
parameters (Å2x 103) for Re2(dppm)2(O2CC6H4NO2)2Cl2·2 THF.
________________________________________________________________________
x
y
z
U(eq)
________________________________________________________________________
H(3)
H(4)
H(6)
H(7)
8827
8144
8134
8846
10235
11732
12470
11053
2677
2322
664
1059
45
53
49
39
H(8A)
H(8B)
H(10)
H(11)
H(12)
H(13)
H(14)
H(16)
H(17)
H(18)
10568
11133
11252
12073
12326
11775
10972
10288
9969
9708
4402
4771
4164
4505
6553
8271
7972
3044
1293
1546
2977
3154
2208
2386
2328
2077
1940
2274
1550
442
37
37
49
55
54
58
46
41
44
55
H(19)
H(20)
H(22)
H(23)
H(24)
H(25)
H(26)
H(28)
H(29)
9768
10070
11085
11416
11631
11472
11106
11732
12470
3571
5300
6924
5791
3638
2592
3698
6287
7546
63
777
4889
5876
5936
4999
3989
3416
3824
50
48
48
57
55
60
46
42
55
H(30)
H(31)
H(32)
H(33A)
H(33B)
H(34A)
H(34B)
12646
12091
11315
10921
10918
10485
10798
9221
9596
8450
-1875
-2352
-474
206
4563
4909
4430
6398
5762
5343
6067
53
53
44
64
64
55
55
147
Table A.5 (continued)
H(35A)
11326
976
5798
58
H(35B)
11108
-12
5185
58
H(36A)
11756
-1351
5814
68
H(36B)
12013
-279
6389
68
________________________________________________________________________
148
Table A.6 Torsion angles [°] for Re2(dppm)2(O2CC6H4NO2)2Cl2·2 THF.
________________________________________________________________
O(1)-C(1)-C(2)-C(7)
-175.8(9)
O(2)-C(1)-C(2)-C(7)
5.7(13)
O(1)-C(1)-C(2)-C(3)
-6.0(13)
O(2)-C(1)-C(2)-C(3)
175.4(9)
C(7)-C(2)-C(3)-C(4)
-3.5(15)
C(1)-C(2)-C(3)-C(4)
-173.3(9)
C(2)-C(3)-C(4)-C(5)
4.2(14)
C(3)-C(4)-C(5)-C(6)
-3.2(15)
C(3)-C(4)-C(5)-N
C(4)-C(5)-C(6)-C(7)
N-C(5)-C(6)-C(7)
C(3)-C(2)-C(7)-C(6)
C(1)-C(2)-C(7)-C(6)
C(5)-C(6)-C(7)-C(2)
C(14)-C(9)-C(10)-C(11)
P(1)-C(9)-C(10)-C(11)
C(9)-C(10)-C(11)-C(12)
C(10)-C(11)-C(12)-C(13)
176.8(9)
1.4(15)
-178.5(8)
1.7(14)
171.1(9)
-0.6(14)
5.4(13)
-168.8(7)
-2.9(14)
-1.0(15)
C(11)-C(12)-C(13)-C(14)
C(10)-C(9)-C(14)-C(13)
P(1)-C(9)-C(14)-C(13)
C(12)-C(13)-C(14)-C(9)
C(20)-C(15)-C(16)-C(17)
P(1)-C(15)-C(16)-C(17)
C(15)-C(16)-C(17)-C(18)
C(16)-C(17)-C(18)-C(19)
C(17)-C(18)-C(19)-C(20)
2.3(15)
-4.1(13)
169.9(7)
0.2(14)
-0.6(13)
-176.9(7)
0.6(14)
0.0(14)
-0.5(15)
C(18)-C(19)-C(20)-C(15)
C(16)-C(15)-C(20)-C(19)
P(1)-C(15)-C(20)-C(19)
C(26)-C(21)-C(22)-C(23)
P(2)-C(21)-C(22)-C(23)
C(21)-C(22)-C(23)-C(24)
C(22)-C(23)-C(24)-C(25)
0.4(15)
0.1(14)
176.7(8)
0.1(15)
-175.1(8)
1.6(17)
-1.9(18)
149
Table A.6 (continued)
C(23)-C(24)-C(25)-C(26)
C(22)-C(21)-C(26)-C(25)
P(2)-C(21)-C(26)-C(25)
C(24)-C(25)-C(26)-C(21)
C(32)-C(27)-C(28)-C(29)
P(2)-C(27)-C(28)-C(29)
C(27)-C(28)-C(29)-C(30)
C(28)-C(29)-C(30)-C(31)
0.5(17)
-1.6(15)
173.5(8)
1.3(17)
-1.9(13)
179.5(7)
2.1(14)
0.6(15)
C(29)-C(30)-C(31)-C(32)
C(30)-C(31)-C(32)-C(27)
C(28)-C(27)-C(32)-C(31)
P(2)-C(27)-C(32)-C(31)
C(4)-C(5)-N-O(4)
C(6)-C(5)-N-O(4)
C(4)-C(5)-N-O(3)
C(6)-C(5)-N-O(3)
O(2)-C(1)-O(1)-Re
C(2)-C(1)-O(1)-Re
-3.5(15)
3.7(14)
-1.0(13)
177.7(7)
177.2(10)
-2.8(14)
-6.5(14)
173.4(9)
3.7(12)
-174.8(6)
O(1)-C(1)-O(2)-Re#1
C(2)-C(1)-O(2)-Re#1
C(16)-C(15)-P(1)-C(9)
C(20)-C(15)-P(1)-C(9)
C(16)-C(15)-P(1)-C(8)
C(20)-C(15)-P(1)-C(8)
C(16)-C(15)-P(1)-Re#1
C(20)-C(15)-P(1)-Re#1
C(14)-C(9)-P(1)-C(15)
13.2(12)
-168.3(6)
114.5(8)
-61.8(8)
9.9(9)
-166.3(7)
-113.2(8)
70.5(8)
138.8(7)
C(10)-C(9)-P(1)-C(15)
C(14)-C(9)-P(1)-C(8)
C(10)-C(9)-P(1)-C(8)
C(14)-C(9)-P(1)-Re#1
C(10)-C(9)-P(1)-Re#1
P(2)-C(8)-P(1)-C(15)
P(2)-C(8)-P(1)-C(9)
-47.1(8)
-116.3(8)
57.8(8)
5.2(8)
179.3(6)
-157.0(5)
100.7(5)
150
Table A.6 (continued)
P(2)-C(8)-P(1)-Re#1
P(1)-C(8)-P(2)-C(27)
P(1)-C(8)-P(2)-C(21)
P(1)-C(8)-P(2)-Re
C(28)-C(27)-P(2)-C(8)
C(32)-C(27)-P(2)-C(8)
C(28)-C(27)-P(2)-C(21)
C(32)-C(27)-P(2)-C(21)
-26.7(5)
-84.0(5)
172.5(5)
42.3(5)
-2.4(9)
179.0(6)
103.6(8)
-75.0(7)
C(28)-C(27)-P(2)-Re
C(32)-C(27)-P(2)-Re
C(26)-C(21)-P(2)-C(8)
C(22)-C(21)-P(2)-C(8)
C(26)-C(21)-P(2)-C(27)
C(22)-C(21)-P(2)-C(27)
C(26)-C(21)-P(2)-Re
C(22)-C(21)-P(2)-Re
C(1)-O(1)-Re-O(2)#1
C(1)-O(1)-Re-Re#1
-124.4(7)
57.0(7)
4.7(9)
179.7(8)
-105.7(8)
69.3(8)
126.3(7)
-58.7(8)
72.4(7)
-15.8(6)
C(1)-O(1)-Re-P(2)
C(1)-O(1)-Re-P(1)#1
C(1)-O(1)-Re-Cl
C(8)-P(2)-Re-O(1)
C(27)-P(2)-Re-O(1)
C(21)-P(2)-Re-O(1)
C(8)-P(2)-Re-O(2)#1
C(27)-P(2)-Re-O(2)#1
C(21)-P(2)-Re-O(2)#1
96.7(11)
-114.4(6)
157.5(7)
-149.8(10)
-28.3(10)
91.7(10)
-125.9(3)
-4.4(3)
115.7(4)
C(8)-P(2)-Re-Re#1
C(27)-P(2)-Re-Re#1
C(21)-P(2)-Re-Re#1
C(8)-P(2)-Re-P(1)#1
C(27)-P(2)-Re-P(1)#1
C(21)-P(2)-Re-P(1)#1
C(8)-P(2)-Re-Cl
-38.0(3)
83.5(3)
-156.5(4)
61.2(3)
-177.3(3)
-57.2(4)
150.3(3)
151
Table A.6 (continued)
C(27)-P(2)-Re-Cl
-88.2(3)
C(21)-P(2)-Re-Cl
31.9(4)
C(36)-O(5)-C(33)-C(34)
-37.9(11)
O(5)-C(33)-C(34)-C(35)
31.9(11)
C(33)-C(34)-C(35)-C(36)
-14.9(11)
C(33)-O(5)-C(36)-C(35)
28.2(12)
C(34)-C(35)-C(36)-O(5)
-7.5(13)
________________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 -x+2,y,-z+1/2
152
Table A.7 Crystallographic details for Mo2(TiPB)2(O2CC2C6H4CH3)2∙4 THF
Molecular formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 27.52°
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole
C68 H92 Mo2 O12
1293.30
150(2) K
0.71073 Å
triclinic
P1
a = 10.9166(1) Å
b = 11.6291(1) Å
c = 13.4313(2) Å
1621.77(3) Å3
1
1.324 Mg/m3
0.446 mm-1
 = 78.634(1)°
 = 84.373(1)°
= 76.304(1)°
680
0.08 x 0.15 x 0.23 mm3
2.53 to 27.52°
-14<=h<=14, -15<=k<=15, -17<=l<=17
42565
7415 [R(int) = 0.043]
99.4 %
Full-matrix least-squares on F2
7415 / 0 / 376
1.053
R1 = 0.0368, wR2 = 0.0925
R1 = 0.0516, wR2 = 0.0987
0.792 and -0.739 e/Å3
153
Table A.8 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters
(Å2x 103) for Mo2(TiPB)2(O2CC2C6H4CH3)2∙4 THF. U(eq) is defined as one third of the
trace of the orthogonalized Uij tensor.
________________________________________________________________________
x
y
z
U(eq)
________________________________________________________________________
C(1)
7135(2)
3326(2)
5557(2)
26(1)
C(2)
8226(2)
2409(2)
5901(2)
31(1)
C(3)
9106(2)
1632(2)
6216(2)
30(1)
C(4)
10155(2)
696(2)
6596(2)
27(1)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
10952(2)
11951(3)
12196(2)
11419(3)
10406(3)
13269(3)
3822(2)
3176(2)
1888(2)
1266(3)
889(2)
-22(3)
-1144(2)
-1316(2)
-426(2)
-2138(3)
3990(2)
3406(2)
3855(2)
3237(3)
7267(2)
7638(2)
7347(2)
6670(2)
6305(2)
7785(3)
6717(2)
7640(2)
7835(2)
8657(2)
34(1)
38(1)
36(1)
37(1)
33(1)
57(1)
24(1)
26(1)
31(1)
40(1)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
1913(3)
3198(3)
3854(3)
1175(3)
349(3)
414(3)
1259(4)
-127(4)
1655(4)
2199(3)
1809(3)
2382(2)
4953(2)
5868(3)
4590(3)
1459(4)
1675(4)
1624(3)
9271(2)
9069(2)
8263(2)
7143(2)
7735(2)
6413(3)
10145(3)
10084(3)
11169(3)
45(1)
44(1)
34(1)
37(1)
46(1)
59(1)
65(1)
91(2)
74(1)
C(24)
C(25)
C(26)
C(27)
C(28A)
C(28B)
C(29)
5253(3)
6016(3)
5437(3)
7369(3)
7869(4)
7895(9)
6869(3)
1898(3)
1491(3)
891(3)
6957(3)
8019(5)
7825(10)
8789(3)
154
8025(2)
8977(3)
7422(3)
6240(3)
5801(7)
5393(13)
5096(3)
42(1)
62(1)
61(1)
55(1)
44(2)*
38(3)*
65(1)
Table A.8 (continued)
C(30)
C(31)
C(32)
C(33)
C(34)
Mo
O(1)
O(2)
5672(3)
2755(6)
3792(6)
3967(6)
2769(6)
5241(1)
6923(2)
3586(2)
8464(2)
4818(5)
4075(6)
4860(6)
5710(6)
5583(1)
4331(1)
6905(1)
5586(2)
150(4)
757(5)
1451(4)
1475(4)
5418(1)
5858(1)
5032(1)
41(1)
107(2)
127(2)
117(2)
112(2)
21(1)
25(1)
25(1)
O(3)
O(4)
O(5)
O(6A)
O(6B)
4333(2)
6174(2)
6039(2)
1984(5)
2593(19)
4849(1)
6397(1)
7228(2)
5484(5)
6073(19)
6764(1)
4111(1)
6088(1)
796(4)
412(16)
23(1)
24(1)
33(1)
124(2)*
113(6)*
*Refined isotropically. The occupancy factor for C(28A) refined to 0.68(2), which
restricted the occupancy factor for C(28B) to 0.32(2). The occupancy factors for O(6A)
and O(6B) were fixed at 0.8 and 0.2, respectively.
________________________________________________________________________
155
Table A.9 Bond lengths [Å] and angles [°] for Mo2(TiPB)2(O2CC2C6H4CH3)2∙4 THF.
_____________________________________________________
C(1)-O(1)
1.274(3)
C(1)-O(2)#1
1.274(3)
C(1)-C(2)
1.443(3)
C(2)-C(3)
1.198(3)
C(3)-C(4)
1.436(3)
C(4)-C(9)
1.394(4)
C(4)-C(5)
1.395(4)
C(5)-C(6)
1.383(4)
C(5)-H(5)
C(6)-C(7)
C(6)-H(6)
C(7)-C(8)
C(7)-C(10)
C(8)-C(9)
C(8)-H(8)
C(9)-H(9)
C(10)-H(10A)
C(10)-H(10B)
0.9500
1.392(4)
0.9500
1.375(4)
1.510(4)
1.378(4)
0.9500
0.9500
0.9800
0.9800
C(10)-H(10C)
C(11)-O(3)
C(11)-O(4)#1
C(11)-C(12)
C(12)-C(13)
C(12)-C(17)
C(13)-C(14)
C(13)-C(18)
C(14)-C(15)
0.9800
1.269(3)
1.278(3)
1.490(3)
1.397(4)
1.406(4)
1.403(4)
1.518(4)
1.398(4)
C(14)-H(14)
C(15)-C(16)
C(15)-C(21)
C(16)-C(17)
C(16)-H(16)
C(17)-C(24)
C(18)-C(19)
0.9500
1.386(4)
1.535(4)
1.386(4)
0.9500
1.523(4)
1.522(4)
156
Table A.9 (continued)
C(18)-C(20)
C(18)-H(18)
C(19)-H(19A)
C(19)-H(19B)
C(19)-H(19C)
C(20)-H(20A)
C(20)-H(20B)
C(20)-H(20C)
1.522(4)
1.0000
0.9800
0.9800
0.9800
0.9800
0.9800
0.9800
C(21)-C(22)
C(21)-C(23)
C(21)-H(21)
C(22)-H(22A)
C(22)-H(22B)
C(22)-H(22C)
C(23)-H(23A)
C(23)-H(23B)
C(23)-H(23C)
C(24)-C(26)
1.481(6)
1.541(5)
1.0000
0.9800
0.9800
0.9800
0.9800
0.9800
0.9800
1.516(4)
C(24)-C(25)
C(24)-H(24)
C(25)-H(25A)
C(25)-H(25B)
C(25)-H(25C)
C(26)-H(26A)
C(26)-H(26B)
C(26)-H(26C)
C(27)-O(5)
1.528(4)
1.0000
0.9800
0.9800
0.9800
0.9800
0.9800
0.9800
1.438(3)
C(27)-C(28A)
C(27)-C(28B)
C(27)-H(27A)
C(27)-H(27B)
C(27)-H(27C)
C(27)-H(27D)
C(28A)-C(29)
1.463(6)
1.529(11)
0.9900
0.9900
0.9900
0.9900
1.515(6)
157
Table A.9 (continued)
C(28A)-H(28A)
C(28A)-H(28B)
C(28B)-C(29)
C(28B)-H(28C)
C(28B)-H(28D)
C(29)-C(30)
C(29)-H(29A)
C(29)-H(29B)
0.9900
0.9900
1.410(10)
0.9900
0.9900
1.500(4)
0.9900
0.9900
C(29)-H(29C)
C(29)-H(29D)
C(30)-O(5)
C(30)-H(30A)
C(30)-H(30B)
C(31)-O(6A)
C(31)-C(32)
C(31)-O(6B)
C(31)-H(31A)
C(31)-H(31B)
0.9900
0.9900
1.442(3)
0.9900
0.9900
1.369(7)
1.460(7)
1.53(2)
0.9900
0.9900
C(31)-H(31C)
C(31)-H(31D)
C(32)-C(33)
C(32)-H(32A)
C(32)-H(32B)
C(33)-C(34)
C(33)-H(33A)
C(33)-H(33B)
C(34)-O(6A)
0.9900
0.9900
1.480(7)
0.9900
0.9900
1.442(7)
0.9900
0.9900
1.411(7)
C(34)-O(6B)
C(34)-H(34A)
C(34)-H(34B)
C(34)-H(34C)
C(34)-H(34D)
Mo-O(3)
Mo-Mo#1
1.43(2)
0.9900
0.9900
0.9900
0.9900
2.103(2)
2.1043(4)
158
Table A.9 (continued)
Mo-O(2)
Mo-O(1)
Mo-O(4)
Mo-O(5)
O(2)-C(1)#1
O(4)-C(11)#1
2.109(2)
2.110(2)
2.112(2)
2.617(2)
1.274(3)
1.278(3)
O(1)-C(1)-O(2)#1
122.5(2)
O(1)-C(1)-C(2)
O(2)#1-C(1)-C(2)
C(3)-C(2)-C(1)
C(2)-C(3)-C(4)
C(9)-C(4)-C(5)
C(9)-C(4)-C(3)
C(5)-C(4)-C(3)
C(6)-C(5)-C(4)
C(6)-C(5)-H(5)
C(4)-C(5)-H(5)
118.9(2)
118.6(2)
177.6(3)
179.7(3)
118.3(2)
121.0(2)
120.7(2)
120.2(3)
119.9
119.9
C(5)-C(6)-C(7)
C(5)-C(6)-H(6)
C(7)-C(6)-H(6)
C(8)-C(7)-C(6)
C(8)-C(7)-C(10)
C(6)-C(7)-C(10)
C(7)-C(8)-C(9)
C(7)-C(8)-H(8)
C(9)-C(8)-H(8)
121.4(3)
119.3
119.3
117.9(2)
121.6(3)
120.5(3)
121.7(3)
119.2
119.2
C(8)-C(9)-C(4)
C(8)-C(9)-H(9)
C(4)-C(9)-H(9)
C(7)-C(10)-H(10A)
C(7)-C(10)-H(10B)
H(10A)-C(10)-H(10B)
C(7)-C(10)-H(10C)
120.6(3)
119.7
119.7
109.5
109.5
109.5
109.5
159
Table A.9 (continued)
H(10A)-C(10)-H(10C)
H(10B)-C(10)-H(10C)
O(3)-C(11)-O(4)#1
O(3)-C(11)-C(12)
O(4)#1-C(11)-C(12)
C(13)-C(12)-C(17)
C(13)-C(12)-C(11)
C(17)-C(12)-C(11)
109.5
109.5
122.0(2)
120.2(2)
117.8(2)
121.6(2)
118.8(2)
119.5(2)
C(12)-C(13)-C(14)
C(12)-C(13)-C(18)
C(14)-C(13)-C(18)
C(15)-C(14)-C(13)
C(15)-C(14)-H(14)
C(13)-C(14)-H(14)
C(16)-C(15)-C(14)
C(16)-C(15)-C(21)
C(14)-C(15)-C(21)
C(15)-C(16)-C(17)
118.3(2)
120.4(2)
121.2(2)
121.1(3)
119.4
119.4
118.5(3)
118.6(3)
122.9(3)
122.6(3)
C(15)-C(16)-H(16)
C(17)-C(16)-H(16)
C(16)-C(17)-C(12)
C(16)-C(17)-C(24)
C(12)-C(17)-C(24)
C(13)-C(18)-C(19)
C(13)-C(18)-C(20)
C(19)-C(18)-C(20)
C(13)-C(18)-H(18)
118.7
118.7
117.9(3)
121.5(2)
120.6(2)
112.4(2)
110.9(2)
111.4(2)
107.3
C(19)-C(18)-H(18)
C(20)-C(18)-H(18)
C(18)-C(19)-H(19A)
C(18)-C(19)-H(19B)
H(19A)-C(19)-H(19B)
C(18)-C(19)-H(19C)
H(19A)-C(19)-H(19C)
107.3
107.3
109.5
109.5
109.5
109.5
109.5
160
Table A.9 (continued)
H(19B)-C(19)-H(19C)
C(18)-C(20)-H(20A)
C(18)-C(20)-H(20B)
H(20A)-C(20)-H(20B)
C(18)-C(20)-H(20C)
H(20A)-C(20)-H(20C)
H(20B)-C(20)-H(20C)
C(22)-C(21)-C(15)
109.5
109.5
109.5
109.5
109.5
109.5
109.5
114.3(3)
C(22)-C(21)-C(23)
C(15)-C(21)-C(23)
C(22)-C(21)-H(21)
C(15)-C(21)-H(21)
C(23)-C(21)-H(21)
C(21)-C(22)-H(22A)
C(21)-C(22)-H(22B)
H(22A)-C(22)-H(22B)
C(21)-C(22)-H(22C)
H(22A)-C(22)-H(22C)
113.4(3)
109.4(3)
106.4
106.4
106.4
109.5
109.5
109.5
109.5
109.5
H(22B)-C(22)-H(22C)
C(21)-C(23)-H(23A)
C(21)-C(23)-H(23B)
H(23A)-C(23)-H(23B)
C(21)-C(23)-H(23C)
H(23A)-C(23)-H(23C)
H(23B)-C(23)-H(23C)
C(26)-C(24)-C(17)
C(26)-C(24)-C(25)
109.5
109.5
109.5
109.5
109.5
109.5
109.5
110.6(3)
111.0(3)
C(17)-C(24)-C(25)
C(26)-C(24)-H(24)
C(17)-C(24)-H(24)
C(25)-C(24)-H(24)
C(24)-C(25)-H(25A)
C(24)-C(25)-H(25B)
H(25A)-C(25)-H(25B)
112.8(3)
107.4
107.4
107.4
109.5
109.5
109.5
161
Table A.9 (continued)
C(24)-C(25)-H(25C)
H(25A)-C(25)-H(25C)
H(25B)-C(25)-H(25C)
C(24)-C(26)-H(26A)
C(24)-C(26)-H(26B)
H(26A)-C(26)-H(26B)
C(24)-C(26)-H(26C)
H(26A)-C(26)-H(26C)
109.5
109.5
109.5
109.5
109.5
109.5
109.5
109.5
H(26B)-C(26)-H(26C)
O(5)-C(27)-C(28A)
O(5)-C(27)-C(28B)
O(5)-C(27)-H(27A)
C(28A)-C(27)-H(27A)
O(5)-C(27)-H(27B)
C(28A)-C(27)-H(27B)
H(27A)-C(27)-H(27B)
O(5)-C(27)-H(27C)
C(28B)-C(27)-H(27C)
109.5
108.9(3)
104.5(4)
109.9
109.9
109.9
109.9
108.3
110.9
110.9
O(5)-C(27)-H(27D)
C(28B)-C(27)-H(27D)
H(27C)-C(27)-H(27D)
C(27)-C(28A)-C(29)
C(27)-C(28A)-H(28A)
C(29)-C(28A)-H(28A)
C(27)-C(28A)-H(28B)
C(29)-C(28A)-H(28B)
H(28A)-C(28A)-H(28B)
110.9
110.9
108.9
104.2(4)
110.9
110.9
110.9
110.9
108.9
C(29)-C(28B)-C(27)
C(29)-C(28B)-H(28C)
C(27)-C(28B)-H(28C)
C(29)-C(28B)-H(28D)
C(27)-C(28B)-H(28D)
H(28C)-C(28B)-H(28D)
C(28B)-C(29)-C(30)
106.1(7)
110.5
110.5
110.5
110.5
108.7
108.9(5)
162
Table A.9 (continued)
C(30)-C(29)-C(28A)
C(30)-C(29)-H(29A)
C(28A)-C(29)-H(29A)
C(30)-C(29)-H(29B)
C(28A)-C(29)-H(29B)
H(29A)-C(29)-H(29B)
C(28B)-C(29)-H(29C)
C(30)-C(29)-H(29C)
103.3(3)
111.1
111.1
111.1
111.1
109.1
109.9
109.9
C(28B)-C(29)-H(29D)
C(30)-C(29)-H(29D)
H(29C)-C(29)-H(29D)
O(5)-C(30)-C(29)
O(5)-C(30)-H(30A)
C(29)-C(30)-H(30A)
O(5)-C(30)-H(30B)
C(29)-C(30)-H(30B)
H(30A)-C(30)-H(30B)
O(6A)-C(31)-C(32)
109.9
109.9
108.3
105.5(2)
110.6
110.6
110.6
110.6
108.8
105.3(5)
C(32)-C(31)-O(6B)
O(6A)-C(31)-H(31A)
C(32)-C(31)-H(31A)
O(6A)-C(31)-H(31B)
C(32)-C(31)-H(31B)
H(31A)-C(31)-H(31B)
C(32)-C(31)-H(31C)
O(6B)-C(31)-H(31C)
C(32)-C(31)-H(31D)
104.2(9)
110.7
110.7
110.7
110.7
108.8
110.9
110.9
110.9
O(6B)-C(31)-H(31D)
H(31C)-C(31)-H(31D)
C(31)-C(32)-C(33)
C(31)-C(32)-H(32A)
C(33)-C(32)-H(32A)
C(31)-C(32)-H(32B)
C(33)-C(32)-H(32B)
110.9
108.9
103.4(5)
111.1
111.1
111.1
111.1
163
Table A.9 (continued)
H(32A)-C(32)-H(32B)
C(34)-C(33)-C(32)
C(34)-C(33)-H(33A)
C(32)-C(33)-H(33A)
C(34)-C(33)-H(33B)
C(32)-C(33)-H(33B)
H(33A)-C(33)-H(33B)
O(6A)-C(34)-C(33)
109.1
103.9(4)
111.0
111.0
111.0
111.0
109.0
108.5(5)
O(6B)-C(34)-C(33)
O(6A)-C(34)-H(34A)
C(33)-C(34)-H(34A)
O(6A)-C(34)-H(34B)
C(33)-C(34)-H(34B)
H(34A)-C(34)-H(34B)
O(6B)-C(34)-H(34C)
C(33)-C(34)-H(34C)
O(6B)-C(34)-H(34D)
C(33)-C(34)-H(34D)
99.9(9)
110.0
110.0
110.0
110.0
108.4
111.8
111.8
111.8
111.8
H(34C)-C(34)-H(34D)
O(3)-Mo-Mo#1
O(3)-Mo-O(2)
Mo#1-Mo-O(2)
O(3)-Mo-O(1)
Mo#1-Mo-O(1)
O(2)-Mo-O(1)
O(3)-Mo-O(4)
Mo#1-Mo-O(4)
109.5
92.65(4)
91.16(6)
91.81(5)
88.52(6)
91.70(5)
176.48(6)
176.61(6)
90.73(4)
O(2)-Mo-O(4)
O(1)-Mo-O(4)
C(1)-O(1)-Mo
C(1)#1-O(2)-Mo
C(11)-O(3)-Mo
C(11)#1-O(4)-Mo
C(27)-O(5)-C(30)
88.45(6)
91.66(6)
117.00(15)
116.88(15)
116.73(15)
117.84(15)
108.3(2)
164
Table A.9 (continued)
C(31)-O(6A)-C(34)
106.9(5)
C(34)-O(6B)-C(31)
97.9(13)
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 -x+1,-y+1,-z+1
165
Table A.10 Anisotropic displacement parameters (Å2x 103) for
Mo2(TiPB)2(O2CC2C6H4CH3)2∙4 THF. The anisotropic displacement factor exponent
takes the form: -22[ h2a*2U11 + ... + 2 h k a* b* U12]
________________________________________________________________________
U11
U22
U33
U23
U13
U12
________________________________________________________________________
C(1)
24(1)
25(1)
24(1)
-1(1)
1(1)
-3(1)
C(2)
31(1)
28(1)
33(2)
-6(1)
-2(1)
-5(1)
C(3)
29(1)
27(1)
30(1)
-1(1)
-1(1)
-4(1)
C(4)
25(1)
24(1)
27(1)
2(1)
0(1)
-2(1)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
35(1)
30(1)
29(1)
47(2)
37(2)
40(2)
23(1)
35(1)
35(1)
39(2)
26(1)
42(2)
33(2)
23(1)
28(1)
52(2)
21(1)
22(1)
30(1)
44(2)
37(2)
37(2)
33(2)
34(2)
32(2)
59(2)
24(1)
22(1)
24(1)
33(2)
-3(1)
1(1)
7(1)
0(1)
-1(1)
9(2)
-1(1)
-2(1)
-4(1)
-5(1)
-3(1)
-7(1)
5(1)
6(1)
-3(1)
1(2)
-1(1)
-1(1)
5(1)
11(1)
-2(1)
-5(1)
3(1)
0(1)
-6(1)
13(2)
1(1)
-6(1)
-6(1)
-9(1)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
57(2)
53(2)
42(2)
33(1)
45(2)
64(2)
74(3)
84(3)
101(3)
42(2)
36(2)
29(1)
35(2)
36(2)
62(2)
61(2)
90(3)
60(2)
31(2)
34(2)
29(2)
35(2)
51(2)
43(2)
45(2)
84(3)
35(2)
5(1)
12(1)
-1(1)
1(1)
-9(1)
-16(2)
12(2)
16(3)
5(2)
8(1)
-2(1)
-2(1)
8(1)
1(1)
-18(2)
17(2)
40(2)
29(2)
-14(2)
-8(1)
-8(1)
2(1)
-1(1)
16(2)
-7(2)
-31(3)
9(2)
C(24)
C(25)
C(26)
C(27)
C(29)
C(30)
C(31)
40(2)
57(2)
50(2)
44(2)
52(2)
41(2)
129(5)
31(2)
52(2)
59(2)
50(2)
51(2)
27(1)
113(4)
45(2)
68(2)
68(2)
72(2)
82(3)
54(2)
84(4)
9(1)
3(2)
-20(2)
9(2)
18(2)
-9(1)
-26(3)
-7(1)
-23(2)
-3(2)
-26(2)
1(2)
-3(1)
-31(3)
-2(1)
2(2)
5(2)
-23(2)
-19(2)
-5(1)
-23(4)
166
Table A.10 (continued)
C(32)
C(33)
C(34)
Mo
O(1)
O(2)
O(3)
O(4)
145(5)
99(4)
140(5)
22(1)
25(1)
25(1)
28(1)
27(1)
116(5)
174(6)
125(5)
19(1)
24(1)
21(1)
21(1)
22(1)
108(5)
88(4)
97(4)
20(1)
26(1)
26(1)
20(1)
23(1)
-28(4)
-11(4)
-39(4)
-3(1)
-4(1)
-5(1)
-3(1)
-3(1)
-43(4)
-22(3)
2(4)
-1(1)
-5(1)
-1(1)
-1(1)
1(1)
18(4)
-51(4)
-67(4)
-3(1)
-3(1)
-1(1)
-5(1)
-6(1)
O(5)
33(1)
32(1)
35(1)
-7(1)
-1(1)
-10(1)
________________________________________________________________________
167
Table A.11 Calculated hydrogen coordinates ( x 104) and isotropic displacement
parameters (Å2x 103) for Mo2(TiPB)2(O2CC2C6H4CH3)2∙4 THF.
________________________________________________________________________
x
y
z
U(eq)
________________________________________________________________________
H(5)
H(6)
H(8)
H(9)
10807
12480
11586
9874
1650
119
-2068
-579
7471
8100
6448
5850
40
45
44
40
H(10A)
H(10B)
H(10C)
H(14)
H(16)
H(18)
H(19A)
H(19B)
H(19C)
H(20A)
13004
14000
13499
390
3647
1818
-339
-5
859
963
-2516
-1802
-2742
3530
1121
5352
5530
6601
6061
3976
8465
7832
7343
8800
9500
6723
8111
7261
8214
6067
86
86
86
48
52
45
69
69
69
89
H(20B)
H(20C)
H(21)
H(22A)
H(22B)
H(22C)
H(23A)
H(23B)
H(23C)
68
-279
1606
-520
-458
-318
1349
2578
1291
5296
4266
595
2495
1097
1575
2466
1407
1104
5909
6795
10094
10188
10611
9412
11249
11184
11726
89
89
79
137
137
137
111
111
111
H(24)
H(25A)
H(25B)
H(25C)
H(26A)
H(26B)
H(26C)
5587
5804
5813
6919
5156
6333
4941
2568
754
2124
1333
203
647
1174
7586
9373
9391
8778
7844
7215
6816
50
93
93
93
92
92
92
168
Table A.11 (continued)
H(27A)
H(27B)
H(27C)
H(27D)
H(28A)
H(28B)
H(28C)
H(28D)
7806
7515
7760
7525
8686
7990
8568
8252
6271
6731
6111
7092
7793
8449
8117
7421
5908
6976
6182
6917
5419
6338
5644
4811
65
65
65
65
53
53
46
46
H(29A)
H(29B)
H(29C)
H(29D)
H(30A)
H(30B)
H(31A)
H(31B)
H(31C)
H(31D)
6833
7033
6830
6979
5287
5056
3077
2295
1974
2971
9656
8595
8952
9525
8988
8549
5349
4309
4515
4832
5056
4404
4347
5310
6084
5068
-436
-108
336
-585
78
78
78
78
49
49
128
128
128
128
H(32A)
4566
3858
322
153
H(32B)
3565
3330
1142
153
H(33A)
4162
4389
2138
141
H(33B)
4658
5275
1186
141
H(34A)
2371
5623
2173
135
H(34B)
2896
6542
1272
135
H(34C)
2092
5324
1832
135
H(34D)
2819
6394
1796
135
________________________________________________________________________
169
Table A.12 Torsion angles [°] for Mo2(TiPB)2(O2CC2C6H4CH3)2∙4 THF.
________________________________________________________________
O(1)-C(1)-C(2)-C(3)
92(7)
O(2)#1-C(1)-C(2)-C(3)
-88(7)
C(1)-C(2)-C(3)-C(4)
23(60)
C(2)-C(3)-C(4)-C(9)
66(55)
C(2)-C(3)-C(4)-C(5)
-114(55)
C(9)-C(4)-C(5)-C(6)
-0.8(4)
C(3)-C(4)-C(5)-C(6)
179.3(2)
C(4)-C(5)-C(6)-C(7)
0.7(4)
C(5)-C(6)-C(7)-C(8)
C(5)-C(6)-C(7)-C(10)
C(6)-C(7)-C(8)-C(9)
C(10)-C(7)-C(8)-C(9)
C(7)-C(8)-C(9)-C(4)
C(5)-C(4)-C(9)-C(8)
C(3)-C(4)-C(9)-C(8)
O(3)-C(11)-C(12)-C(13)
O(4)#1-C(11)-C(12)-C(13)
O(3)-C(11)-C(12)-C(17)
0.6(4)
-178.2(3)
-1.7(4)
177.1(3)
1.6(4)
-0.2(4)
179.6(2)
90.7(3)
-88.5(3)
-92.7(3)
O(4)#1-C(11)-C(12)-C(17)
C(17)-C(12)-C(13)-C(14)
C(11)-C(12)-C(13)-C(14)
C(17)-C(12)-C(13)-C(18)
C(11)-C(12)-C(13)-C(18)
C(12)-C(13)-C(14)-C(15)
C(18)-C(13)-C(14)-C(15)
C(13)-C(14)-C(15)-C(16)
C(13)-C(14)-C(15)-C(21)
88.0(3)
-1.8(4)
174.7(2)
-179.3(2)
-2.8(4)
0.1(4)
177.5(3)
2.0(5)
-176.9(3)
C(14)-C(15)-C(16)-C(17)
C(21)-C(15)-C(16)-C(17)
C(15)-C(16)-C(17)-C(12)
C(15)-C(16)-C(17)-C(24)
C(13)-C(12)-C(17)-C(16)
C(11)-C(12)-C(17)-C(16)
C(13)-C(12)-C(17)-C(24)
-2.4(5)
176.5(3)
0.7(4)
-176.8(3)
1.5(4)
-175.0(2)
179.0(2)
170
Table A.12 (continued)
C(11)-C(12)-C(17)-C(24)
C(12)-C(13)-C(18)-C(19)
C(14)-C(13)-C(18)-C(19)
C(12)-C(13)-C(18)-C(20)
C(14)-C(13)-C(18)-C(20)
C(16)-C(15)-C(21)-C(22)
C(14)-C(15)-C(21)-C(22)
C(16)-C(15)-C(21)-C(23)
2.5(4)
-133.2(3)
49.4(4)
101.3(3)
-76.1(3)
-159.7(4)
19.2(5)
71.9(4)
C(14)-C(15)-C(21)-C(23)
C(16)-C(17)-C(24)-C(26)
C(12)-C(17)-C(24)-C(26)
C(16)-C(17)-C(24)-C(25)
C(12)-C(17)-C(24)-C(25)
O(5)-C(27)-C(28A)-C(29)
C(28B)-C(27)-C(28A)-C(29)
O(5)-C(27)-C(28B)-C(29)
C(28A)-C(27)-C(28B)-C(29)
C(27)-C(28B)-C(29)-C(30)
-109.2(4)
81.6(4)
-95.9(3)
-43.3(4)
139.2(3)
-17.5(7)
65.8(11)
22.5(12)
-81.5(13)
-10.1(13)
C(27)-C(28B)-C(29)-C(28A)
C(27)-C(28A)-C(29)-C(28B)
C(27)-C(28A)-C(29)-C(30)
C(28B)-C(29)-C(30)-O(5)
C(28A)-C(29)-C(30)-O(5)
O(6A)-C(31)-C(32)-C(33)
O(6B)-C(31)-C(32)-C(33)
C(31)-C(32)-C(33)-C(34)
C(32)-C(33)-C(34)-O(6A)
70.4(13)
-77.3(12)
29.2(6)
-5.9(9)
-30.7(5)
-34.4(7)
10.8(10)
22.3(7)
-3.4(7)
C(32)-C(33)-C(34)-O(6B)
O(2)#1-C(1)-O(1)-Mo
C(2)-C(1)-O(1)-Mo
O(3)-Mo-O(1)-C(1)
Mo#1-Mo-O(1)-C(1)
O(2)-Mo-O(1)-C(1)
O(4)-Mo-O(1)-C(1)
-49.3(11)
3.9(3)
-175.51(17)
90.86(17)
-1.74(16)
175.7(10)
-92.52(17)
171
Table A.12 (continued)
O(3)-Mo-O(2)-C(1)#1
Mo#1-Mo-O(2)-C(1)#1
O(1)-Mo-O(2)-C(1)#1
O(4)-Mo-O(2)-C(1)#1
O(4)#1-C(11)-O(3)-Mo
C(12)-C(11)-O(3)-Mo
Mo#1-Mo-O(3)-C(11)
O(2)-Mo-O(3)-C(11)
-94.80(17)
-2.12(16)
-180(36)
88.56(17)
-1.7(3)
179.07(16)
1.08(15)
92.95(16)
O(1)-Mo-O(3)-C(11)
O(4)-Mo-O(3)-C(11)
O(3)-Mo-O(4)-C(11)#1
Mo#1-Mo-O(4)-C(11)#1
O(2)-Mo-O(4)-C(11)#1
O(1)-Mo-O(4)-C(11)#1
C(28A)-C(27)-O(5)-C(30)
C(28B)-C(27)-O(5)-C(30)
C(29)-C(30)-O(5)-C(27)
C(32)-C(31)-O(6A)-C(34)
-90.55(16)
176.2(9)
-174.8(9)
0.40(15)
-91.39(16)
92.12(16)
-1.8(5)
-26.6(8)
20.7(3)
32.9(7)
O(6B)-C(31)-O(6A)-C(34)
-61.7(11)
O(6B)-C(34)-O(6A)-C(31)
67.1(12)
C(33)-C(34)-O(6A)-C(31)
-18.4(7)
O(6A)-C(34)-O(6B)-C(31)
-52.6(9)
C(33)-C(34)-O(6B)-C(31)
53.7(11)
O(6A)-C(31)-O(6B)-C(34)
57.3(10)
C(32)-C(31)-O(6B)-C(34)
-40.2(12)
________________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 -x+1,-y+1,-z+1
172
APPENDIX B
SPECTROSCOPIC DATA FOR Mo2(TiPB)2(O2CC2C6H4CH3)2,
W2(T PB)2(O2CC2C6H4CH3)2, Mo2(TiPB)2(O2CC2-9-C14H9)2, W2(TiPB)2(O2CC2-9C14H9)2
i
173
0
0
-2
-2
-4
-4
-6
-8
-6
1a
2a
0
0
-1
-1
-2
-2
-3
-4
-3
1b
2b
-5
2400
2200
2000
1800
1600
1400
1200
1000
2400
2200
2000
1800
1600
1400
1200
1000
Wavenumber / cm-1
Wavenumber / cm-1
Figure B.1 Ground state infrared absorption spectra of 1a, 2a, 1b, 2b in THF solution.
In spectra shown THF is subtracted.
174
Figure B.2 Time-resolved (fs) infrared absorption spectra of asymmetric carboxylate
stretch of TiPB ligands of 1a in THF. The carboxylate signal is shifted to higher energy in
the excited state due to decreased backbonding from the positively charged dimetal center
(exc = 400 nm).
175
Figure B.3 Time-resolved (fs) infrared absorption spectra of 2a in THF. The initial <1 ps
rise which blue shifts signal is attributed to vibrational cooling (exc = 514 nm).
176
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