Doctoral Consortium e-poster Research Week 2009-2010
15-19 February 2010
“The Great Divide”: Carbene 
Silylene
 Germylene”
Presented by: BUNDHUN Ashwini (MPhil/PhD)
Department of Chemistry,
University of Mauritius, Mauritius
Advisors:
Assoc. Prof. Ponnadurai Ramasami
(ramchemi@intnet.mu)
University of Mauritius, Mauritius
Prof. Henry F. Schaefer III
Centre for Computational Quantum Chemistry (CCQC)
University of Georgia, Athens, Georgia, USA

Ashwini Bundhun
Advisors : Assoc. Prof. (Dr) Ponnadurai Ramasami & Prof. Henry. F. Schaefer III
BSc Chemistry
University of Mumbai
India
MSc in Chemistry
University of Mauritius
Mauritius ashwinibilly@gmail.com
Research Interests :
Benchmarking Density Functional Theory (DFT) functionals against experimental data and high-quality computations on GeX
2 and GeXY (X, Y = H, F, Cl, Br, I, CN, CH
3
, SiH
3
, GeH
3
) germylene derivatives and their tin analogues. These studies consist of the predicted trends in the geometrical parameters, the different forms of electron affinities and singlet-triplet gaps.
My current research also focuses on the “Quantum Mechanical Modeling for the GeX
2
/GeHX + GeH
4
Reactions (X = H, F, Cl, and Br)”. I am using DFT to study in all seven reactions in the gas-phase and the stationary points on the potential energy surface are characterized. The gist is that the energetics for the
GeH
2
+ GeH
4

Ge
2
H
6 system is consistent vis-à-vis available experimental data. Hence the trend in the energetics and thermochemical data for the all mono- and di-substituted systems are further studied and compared to the parent reaction.
Other interests :
DFT study of the carbon chains C n
X, C n
X + and C n
X
–
(X = O and Se; n = 1–10).
DFT study of dicyanogermylenes and XGeCY
3 species (X, Y = H, F, Cl, Br, I).
2

“Presentation Overview”
Introduction – Importance of germylene species, Application processes
Theoretical Methods – Programs Suite, Optimization, Functionals, Basis sets
Geometrical Parameters – Symmetries, States, Multiplicities,
Bond lengths, Bond angles
Predicted trends in:-
Singlet-Triplet Gaps
Electron Affinities
Graphical representation of singlet-triplet gaps and electron affinities
Conclusions
Acknowledgements
3

“Introduction”
•
Germylenes : Divalent germanium compounds are important chemical species
Intermediates in processes employed in the semiconductor industry
Processes:
Plasma-etching
Chemical vapor deposition (CVD)
Areas in which electron affinities play important roles:
Microelectronics
Silicon
Schottky diodes
Molecular clusters
Polymer photoluminescence
4

“Theoretical Methods”
Program Suite : Gaussian 03 & GaussView
Functionals : BH&HLYP, BLYP and B3LYP
Basis sets : DZP++ for all atoms except the 6-311G(d,p) for iodine atom
Frequency Analysis : Harmonic vibrational frequencies
Predicted are the four different forms of electron affinities:
Adiabatic electron affinities (EA ad
)
Corrected adiabatic electron affinity (EA ad(ZPVE)
)
Vertical electron affinity (VEA) & Vertical detachment energy of the anion (VDE)
Singlet-triplet splittings
5 http://www.gaussian.com/

“Theoretical Computations”
EA ad
= E(optimized neutral) − E(optimized anion)
EA vert
= E(optimized neutral) − E(anion at optimized neutral geometry)
VDE = E(neutral at optimized anion geometry) – E(optimized anion) [3]
EA ad(ZPVE)
= [E(optimized neutral) + ZPVE neutral
] – [E(optimized anion) + ZPVE anion
] [4]
The singlet-triplet splittings are predicted as the energy difference between the neutral ground state and the lowest triplet state.
[1]
[2]
6

Energy (eV)
“Potential Energy Surfaces”
1.0
X
–
X

= 2

= 1

= 0, J

= 0
VDE EA VEA
0.5
1.0
2.0

= 2

= 1

= 0, J

= 0 r/Å
Rienstra-Kiracofe J. C.; Tschumper G. S; Schaefer H. F.; Nandi S.; Ellison B. Chem. Rev. 2002 , 102 , 231.
Potential energy surfaces representing diatomic and polyatomic molecules for an anionic molecule, X– and its corresponding neutral molecule X.
The transitions show the adiabatic electron affinity (EA), vertical electron affinity (VEA) and vertical detachment energy (VDE).
For the non-linear and polyatomic molecules with n number of atoms, there are (3 n
– 6) modes allowing a cut through the active mode(s).
7

“Multiplicities of Carbene Analogues”
Methylene is a ground state triplet
Silylene and germylene are ground state singlets a
1 a
1 a
1 b
1
C Si Ge
Triplet 3 B
1
Singlet 1 A
1
Singlet 1 A
1
In all MH
2
(C, Si and Ge) species with six valence electrons the singlet state has two electrons in an orbital of

-symmetry (a
1
). In the triplet state this electron pair is unpaired and one electron resides in an orbital of

-symmetry (b
1
)
8

“HOMO-LUMO Gaps in SiH
2 and GeH
2 larger than in CH
2
”
Energy
(Units)
2b
2
3a
1
1b
1
2a
1
1a
1
Apeloig Y.; Pauncz R.; Karni M.; West R., Steiner W.; Chapman D. Organometallics 2003 , 22 , 3250.
1b
2
9

Table 1. Experimental structural parameters, singlet-triplet gaps, electron affinities (eV) for the carbon and silicon analogues.
M
MH
MF
2
2
MCl
2
C r(C-H) = 1.078
Å
,

(H-C-H) = 136.0
 r(C-H) = 1.077 Å,

(H-C-H) = 134.0
 r(C-H) = 1.107 Å,

(H-C-H) = 102.4


E
S-T
= 9.09

0.20 kcal mol -1
EA = 0.6520 ± 0.0060 kcal mol -1
EA = 0.210 ± 0.015 kcal mol -1
EA = 0.208 ± 0.031 kcal mol -1
EA > 0.90 ± 0.40 kcal mol -1 r(C-F) = 1.304
Å
,

(F-C-F) = 104.8
 r(C-F) = 1.300 Å,

(F-C-F) = 104.9


E
S-T
= 237.14

0.02 kJ mol -1
EA = 0.180 ± 0.020 kcal mol -1 87
EA = 0.1790 ± 0.0050 kcal mol -1
EA = 0.07 ± 0.15 kcal mol -1
EA = < 1.30 ± 0.80 kcal mol -1
EA > 0.2005 kcal mol -1
EA = 2.6495 kcal mol -1 r(C-Cl) = 1.716
Å
,

(Cl-C-Cl) = 109.2
 r(C-Cl) = 1.714 Å,

(Cl-C-Cl) = 109.3

MBr
2 r(C-Br) = 1.740
Å
,

(Br-C-Br) = 112.0

EA = 1.928 ± 0.082 kcal mol -1
EA = 1.880 ± 0.070 kcal mol -1
Si r(Si-H) = 1.514
Å
,

(H-Si-H) = 92.1
 r(Si-H) = 2.861 Å,

(H-Si-H) = 92.0

EA = 1.123 ± 0.022 kcal mol -1 r(Si-F) = 1.590
Å
,

(F-Si-F) = 100.8
 r(Si-F) = 1.586 Å,

(F-Si-F) = 113.1

EA = 0.10 ± 0.10 kcal mol -1 r(Si-Cl) = 2.088
Å
,

(Cl-Si-Cl) = 102.8
 r(Si-Cl) = 2.041 Å,

(Cl-Si-Cl) = 114.5

EA = 0.77 ± 0.13 kcal mol -1 r(Si-Br) = 2.249
Å
,

(Br-Si-Br) = 102.7

EA > 1.7 kcal mol -1
10
All references are listed in Table 6.
Bundhun A.; Ramasami P.; Schaefer H. F. J. Phys. Chem. A 2009 , 113, 8080.

“Structural Parameters of Germylene Derivatives”
GeH
2
Neutral ( 1 A
1
)
B3LYP 1.601 Å
BLYP 1.618 Å
BHLYP 1.584 Å
90.7

90.2

91.5

GeH
2
¯ Anion ( 2 B
1
)
1.629 Å
1.647 Å
1.612 Å
91.5

91.2

92.2

GeH
2
Triplet ( 3 B
1
)
1.548 Å
1.565 Å
1.533 Å
119.6

119.5

119.6

GeF
2
Neutral ( 1 A
1
)
B3LYP 1.771 Å
BLYP 1.798 Å
BHLYP 1.744 Å
97.6

98.4

96.8

1.863 Å
1.893 Å
1.834 Å
GeF
2
¯ Anion ( 2 B
1
)
96.1

97.2

95.0

GeF
2
Triplet ( 3 B
1
)
1.769 Å
1.802 Å
1.738 Å
115.0

116.0

113.8

GeCl
2
Neutral ( 1 A
1
)
B3LYP 2.226 Å
BLYP 2.254 Å
BHLYP 2.200 Å
100.8

101.7

100.0

2.394 Å
2.425 Å
2.368 Å
GeCl
2
¯ Anion ( 2 B
1
)
100.8

102.3

99.5

GeCl
2
Triplet ( 3 B
1
)
2.210 Å
2.251 Å
2.176 Å
119.2

119.9

118.4

11

“Structural Parameters of Germylene Derivatives”
GeBr
2
Neutral ( 1 A
1
)
B3LYP 2.383 Å
BLYP 2.413 Å
BHLYP 2.358 Å
102.2

103.2

101.3

GeBr
2
¯ Anion ( 2 B
1
)
2.556 Å
2.588 Å
2.532 Å
102.3

103.8

101.0

GeBr
2
Triplet ( 3 B
1
)
2.369 Å
2.411 Å
2.334 Å
121.1

121.6

120.4

B3LYP 2.611 Å
BLYP 2.643 Å
BHLYP 2.587 Å
GeI
2
Neutral ( 1 A
1
)
103.9

105.0

103.0

Ge(CN)
2
Neutral ( 1 A
1
)
B3LYP 1.987 Å
BLYP 2.005 Å
BHLYP 1.972 Å
93.0

93.3

92.9

170.5

169.7

171.5

1.172 Å
1.187 Å
1.156 Å
GeI
2
¯ Anion ( 2 B
1
)
2.786 Å
2.819 Å
2.764 Å
104.2

105.7

102.8

Ge(CN)
2
¯ Anion ( 2 B
1
)
2.022 Å
2.038 Å
2.012 Å
170.2

169.3

171.3

93.4

94.0

92.8

1.178 Å
1.192 Å
1.162 Å
GeI
2
Triplet ( 3 B
1
)
2.596 Å
2.641 Å
2.560 Å
122.0

121.9

121.8

Ge(CN)
2
Triplet ( 3 B
1
)
1.893 Å
1.912 Å
1.881 Å
1.175 Å
1.191 Å
1.158 Å
117.0
115.9


117.0


174.2

174.4

174.7


12
Supporting Information Available via the internet at J. Phys.Chem. A 2009 , 113 , 8080. http://pubs.acs.org
.

More Compounds
Ge(CH
3
)
2
Ge(SiH
3
)
2
Table 1. Experimental Techniques
•
•
•
•
•
•
Electron impact appearance energy
Laser photoelectron spectroscopy
UV photoelectron spectroscopy
Microwave spectroscopy
Infrared spectroscopy
Laser-induced fluorescence spectroscopy
Ge(GeH
3
)
2
Table 2. Experimental structural parameters, singlet-triplet gaps, electron affinities (eV) of available germylene derivatives.
EA (GeH
2
) = 1.0970 ± 0.0027 kcal mol -1
EA (GeF
2
) > 1.30 ± 0.30 kcal mol -1
EA (GeCl
2
) = 2.56 kcal mol -1
EA (GeBr
2
) >1.6 kcal mol -1
13
Supporting Information Available via the internet at J. Phys.Chem. A 2009 , 113 , 8080. http://pubs.acs.org
.

“Predicted Electron Affinities and Singlet-Triplet Gaps”
BH&HLYP BLYP B3LYP BH&HLYP BLYP B3LYP
Ge H
2
Ge F
2
Ge Cl
2
Ge Br
2
Ge I
2
Ge (CN)
2
1.01 (1.03) 1.02 (1.05) 1.15 (1.18)
0.85 (0.87) 0.81 (0.83) 0.96 (0.98)
1.65 (1.66) 1.49 (1.50) 1.69 (1.70)
1.81 (1.82) 1.60 (1.61) 1.83 (1.84)
2.06 (2.07) 1.76 (1.77) 2.03 (2.04)
2.73 (2.56) 2.56 (2.73) 2.78 (2.78)
Ge (CH
3
)
2
Ge (SiH
3
)
2
Ge (GeH
3
)
2
0.44 (0.46) 0.49 (0.52) 0.60 (0.62)
1.87 (1.90) 1.83 (1.86) 1.99 (2.06)
1.91 (1.95) 1.89 (1.93) 2.04 (2.08)
Table 3. Germylene adiabatic electron affinities EA ad and zero-point corrected EA ad values (in parentheses) in eV.
Ge H
2
Ge F
2
Ge Cl
2
Ge Br
2
Ge I
2
Ge (CN)
2
1.06 (24.4) 1.23 (28.3) 1.16 (26.7)
3.57 (82.4) 3.72 (85.9) 3.69 (85.0)
2.66 (61.4) 2.83 (65.2) 2.78 (64.1)
2.38 (54.8) 2.52 (58.1) 2.48 (57.2)
2.08 (47.9) 2.05 (47.2) 2.07 (47.7)
1.76 (40.6) 1.87 (43.2) 1.85 (42.7)
Ge (CH
3
)
2
1.26 (29.1) 1.38 (31.9) 1.34 (31.0)
Ge (SiH
3
)
2
Ge (GeH
3
)
2
0.48 (11.0) 0.68 (15.6) 0.60 (13.8)
0.57 (13.2) 0.77 (17.8) 0.69 (16.0)
Table 4. Singlet-triplet gaps (eV) (kcal mol -1 in parentheses).
14

“Predicted VEA and VDE”
Ge H
2
Ge F
2
Ge Cl
2
Ge Br
2
Ge I
2
Ge (CN)
2
Ge (CH
3
)
2
Ge (SiH
3
)
2
Ge (GeH
3
)
2
BH&HLYP
0.99
0.69
1.38
1.56
1.84
2.78
0.35
1.66
1.72
BLYP
1.01
0.67
1.25
1.39
1.58
3.06
0.36
1.61
1.70
B3LYP
1.14
0.81
1.44
1.60
1.83
2.71
0.51
1.78
1.84
Table 5. Vertical electron affinity (VEA) in eV.
BH&HLYP BLYP B3LYP
Ge H
2
Ge F
2
Ge Cl
2
Ge Br
2
Ge I
2
Ge (CN)
2
Ge (CH
3
)
2
Ge (SiH
3
)
2
Ge (GeH
3
)
2
1.02
1.04
1.97
2.11
2.32
2.80
0.50
2.04
2.08
1.03
0.98
1.76
1.86
1.97
2.35
0.53
1.99
2.05
1.16
1.14
1.99
2.10
2.26
2.76
0.66
2.19
2.20
Table 6. Vertical detachment energy (VDE) in eV.
BHLYP functional provides the best agreement of the predicted structures with experimentally geometrical parameters
15

“Graphical :- Electron Affinities & Singlet-Triplet Gaps”
3.00
2.50
2.00
1.50
1.00
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0
0.50
0 2 3 4 5 6 7
1 2 3 4 5 6
H F Cl Br I CN
7
Graph of adiabatic electron affinities EA ad(ZPVE) halogen substituents.
(eV) versus Graph of singlet-triplet gaps (eV) versus halogen substituents.
16

“Graphical :- Electron Affinities & Singlet-Triplet Gaps”
4
2.3
2.1
1.9
1.7
1.5
1.3
1.1
0.9
0.7
0.5
0 H F CH
3
SiH
3
GeH
3
Graph of adiabatic electron affinities EA ad(ZPVE)
H, F, CH
3
, SiH
3 and GeH
3 substituents.
(eV) versus
3.5
3
2.5
2
1.5
1
6
0.5
0 1 2 3
H F CH
3
4
SiH
3
5
GeH
3
.
Graph of singlet-triplet (eV) versus H, F, CH
3
, SiH
3
GeH
3 substituents.
and
6
17

“Factors Affecting Electron Affinities”
Electronegativities of the halo-substituents
Size of the central divalent germanium centre
Size of the halogen substituents
Electron density clouding the divalent germanium centre
Interelectron repulsion
Electronegative substituents withdraw electron density from Ge resulting in more positive charge making Ge a better

-acceptor, enhancing

-donation from the halo-substituents
18

“Fluoro Substituents”
EA ad(ZPVE) containing fluoro substituents decreases sharply due to:
Shortness of the Ge-F bond distance
Fluorine lone pair crowds into the germanium

-orbital
4p contribution of the Ge atom higher in the singlet states
4s contribution of the Ge atom is less in the triplet state
Enhanced polarity of the Ge-F bond :- polarizability effect
19

“Chloro/bromo/iodo Substituents”
Ge-Cl, Ge-Br and Ge-I bonds are less polarized
Poorer
 withdrawing abilities of the Ge-Cl, Ge-Br and Ge-I bonds
Less effective donor abilities of non-bonding electron pairs
Accounting for the sizes of the Chloro/bromo/iodo substituents
No large difference in the withdrawing abilities of the Ge-Cl/Ge-Br/Ge-I bonds
20

“Standard Pauling Electronegativities”
F(3.98) > Cl (3.16) > Br (2.96) > I (2.66) > C (2.55) > H (2.20) > Ge (2.01) > Si (1.90)
Electronegative substituents withdraw charge from the divalent germanium centre leading to an increase in the central atom’s positive charge
Despite electronegativities decrease in the order F > Cl > Br > I , EA ad(ZPVE) increases in the opposite order
Hence electronegativity is not the sole factor in determining the ability of germylenes to accept an extra electron
21
Allfred A. L. J. Inorg. Nucl. Chem . 1961 , 17 , 215.

“Conclusions”
Dimethylgermylene also binds an electron, though weakly, ranging from 0.44 eV – 0.60 eV
Down the periodic table, there is an increasing ability to bind an electron
GeH
3 and SiH
3 groups behave similarly
No neutral structure of C
2v symmetry was found for Ge(CH
3
)
2 on the PES
Singlet-triplet splittings for germylene derivatives are consistently larger than those for methylene and silylene
22

“Conclusions”
EA ad(ZPVE) values (eV) obtained with the B3LYP functional range from 0.62 eV to [Ge(CH
3
)
2
] to
2.08 eV [Ge(GeH
3
)
2
]
Results compare satisfactorily with the few available experimental values
Largest singlet-triplet gaps is predicted for GeF
2
, with Ge(GeH
3
)
2 value of 0.57 eV having the smallest
Singlet-triplet splittings for germylene derivatives are consistently larger than those for methylene and silylene
Invariably, as one progresses down the periodic table C

Si
 Ge, the “great divide” occurs between carbon and silicon
23

“Acknowledgments”
Hassan H. Abdallah (Universiti Sains Malaysia)
Paul Blowers (The University of Arizona)
Centre for Computational Quantum Chemistry (CCQC)
Facilities at the University of Mauritius (UOM)
Mauritius Tertiary Education Commission (TEC)
Reviewers
The Organizing Committee of Doctoral Consortium
24

“Representative Publications”
“Germylene Energetics: Electron Affinities and Singlet−Triplet Gaps of GeX
2
(X, Y = H, CH
3
, SiH
3
, GeH
3
, F, Cl, Br, I)” and GeXY Species
Bundhun A.; Ramasami P.; Schaefer H. F. J. Phys. Chem. A 2009, 113, pp 8080–8090.
-------------------------------------------------------------------------------------------------------------------------------
“Quantum Mechanical Modeling for the GeX
2
/GeHX + GeH
4
Reactions (X = H, F, Cl, and Br)”
Bundhun A.; Blowers P.; Ramasami P.; Schaefer H. F. J. Phys. Chem. A (Accepted Manuscript)
---------------------------------------------------------------------------------------------------
“DFT study of the carbon chains C n
X, C n
X + and C n
X
–
(X = O and Se; n = 1–10)”
Bundhun A.; Ramasami P. EPJ D (Accepted Manuscript)
---------------------------------------------------------------------------------------------------------------
25