Halogen Bonding
Darin J. Ulness
Department of Chemistry
Concordia College, Moorhead, MN
Outline
• Hydrogen bonding
• History
• The s hole and s hole bonding
• I(2)CARS Spectroscopy
• Data
• Discussion
Hydrogen Bonding
•Hydrogen on a N, O, F
•Interact with a N, O, F
•Bond distance shorter than
sum of Van der Waals Radii
•Angle approximately 180o
Halogen Bonding
•I > Br > Cl, no F
•Interact with a N, O
•Bond distance shorter than
sum of Van der Waals Radii
•Angle approximately 180o
Halogen Bonding: History
•F. Guthrie, J. Chem. Soc. 16, 239 (1863)
•Complexation of I2 and NH3
•I. Remsen, J.F. Norris, Am. Chem. J. 18, 90, (1896)
•Complexation of X2 and methyl amines
•O. Hassel, Proc. Chem. Soc. 7, 250 (1957) [Nobel Prize 1969]
•Donor/acceptor complexes: Halogens and Lone Pair
•T. Di Paolo, C. Sandorfy, Can. J. Chem. 52, 3612 (1974)
•Spectroscopic studies aromatic amines and halo-alkanes
Halogen Bonding: Today
Biochemistry
• Biomolecular engineering
• Drug Design
Materials Science
• Crystal engineering
• Molecular recognition
Halogen Bonding
Computational
Chemistry
• s hole bonding
Voth A. R. et.al. PNAS 2007;104:6188-6193
Resnati et.al. J. Fluroine Chem.
2004;104: 271
The s hole
Test charge far from an iodine atom
I
Test Charge
Free Iodine
Atom
Test Charge “feels” an electroneutral field
The s hole
Test charge close to an iodine atom
I
Test Charge “feels” an electropositive
field
An arbitrary spherical surface carries
an eletropositive potential !
The s hole
Test Charge
In molecules the electron density is
directed into the bond
The s hole
Electropositve
s-hole
Test Charge
Electroneutral
“ring”
Electronegative
“belt”
The s hole
Perfluoroinate: Stronger s hole
Electropositve
s-hole
Test Charge
Electroneutral
“ring”
Electronegative
“belt”
s hole bonding with
pyridine
Pyridine as a probe of
Halogen bonding
The ring stretches of pyridine act as a probe of its
environment
N
N
C
C
C
C
C
C
C
C
C
C
“ring-breathing” mode
“triangle” mode
Pyridine as a probe of
Halogen bonding
Hydrogen bonding to a water modulates the stretching
frequency
H
H
O
N
N
C
C
C
C
C
C
C
C
C
free pyridine
C
H-bonded pyridine
Experiment
•Coherent Raman Scattering: e.g.,
CARS
•Frequency resolved signals
•Spectrograms
•Molecular liquids
Light
Electromagnetic radiation
•Focus on electric field part
Spectrum
frequency
One frequency (or color)
time
Noisy Light: Definition
Eletric Field Strength
Noisy Light Spectrum
Time resolution on
•Broadband
the order of the
•Phase incoherent
•Quasi continuous wave correlation time, tc
Frequency
Time
Nonlinear Optics
Material
Signal
P= c E
Light field
Perturbation series approximation
P(t) = P(1) + P(2) + P(3) …
P(1) = c (1)E,
P(2) = c (2)EE,
P(3) = c (3)EEE
CARS
Coherent Anti-Stokes Raman Scattering
w1
w2
w1
wCARS
w1-w2= wR
wCARS= w1 +wR
wR
CARS with Noisy Light
•I(2)CARS
•We need twin noisy beams B and B’.
•We also need a narrowband beam, M.
•The frequency of B (B’) and M differ by
roughly the Raman frequency of the sample.
•The I(2)CARS signal has a frequency that is
anti-Stokes shifted from that of the noisy
beams.
B
M
B’
I(2)CARS
(2)
I CARS:
Experiment
Computer
CCD
Interferometer
Monochromator
B’
Sample
t
B
I(2)CARS
M
Lens
Narrowband
Source
Broadband
Source
(noisy light)
(2)
I CARS:
Spectrogram
Computer
CCD
Interferometer
Monochromator
t
B’
Sample
B
I(2)CARS
M
Lens
Narrowband
Source
Broadband
Source
•Signal is dispersed onto the CCD
•Entire Spectrum is taken at each
delay
•2D data set: the Spectrogram
•Vibration information
(2)
I CARS:
Data Processing
BenzeneT22
BenzeneT22
150
2
125
1
Fourier
100
0
75
Transformation
-1
50
25
-2
0
18000
18100
18200
18300
100
18400
0
200
300
200
400
600
800
1000
400
0.8
0.6
0.4
0.2
X-Marginal
1200
Pyridine as a probe of
Halogen bonding
Normalized X-marginal
1.0
0.8
0.6
0.4
0.2
0.0
980
1000
1020
1040
-1
Wavenumber / cm
Pyridine as a probe of
Halogen bonding
ring-breathing
Normalized X-marginal
1.0
0.8
free
pyridine
100% pyr
85% pyr
70% pyr
55% pyr
25% pyr
H-bonded
pyridine
0.6
0.4
0.2
0.0
980
1000
1020
1040
-1
Wavenumber / cm
Pyridine as a probe of
Halogen bonding
1-iodo-perfluoroalkanes
2-iodo-perfluoropropane
C3F7I
C6F13I
C4F9I
1-iodo-perfluoroalkanes
C4F9I
C6F13I
C6F13I and Pyridine
4
4
3.5
3.5
Neat
0.1
2.5
0.2
0.3
2
0.4
0.5
0.6
1.5
0.7
.8
1
0.9
3
Neat
Normalized Intesity
3
0.1
2.5
0.2
0.3
2
0.4
0.5
1.5
0.6
0.7
1
.8
0.9
0.5
0.5
0
0
900
920
940
960
980
1000
1020
1040
1060
1080
1100
900
920
940
960
980
1000
1020
Frequency (cm-1)
1040
1060
1080
1100
2-iodo-perfluoropropane
C3F7I
C6F13I
C6F13I and Pyridine
4
0.1
3.5
0.2
3
0.3
2.5
2
1.5
1
3.5
3
Neat
Normalized Intesity
Normalized Intensity
Pyridine and C3F7I
4
0.4
2.5
0.5
2
0.6
1.5
0.7
1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
.8
0.9
0.5
0.8
0
900
920
940
960
980
1000
1020
Frequency (cm-1)
1040
1060
1080
1100
0.9
Neat
0.5
0
900
920
940
960
980
1000
1020
Frequency (cm-1)
1040
1060
1080
1100
Temperature Studies
C3F7I
C6F13I
C3F7I Temp Study
Name
4.5
4.5
Normalized Intensity
3.5
3
2.5
2
1.5
1
0.5
0
900
920
940
960
980
1000
1020
Frequency (cm-1)
1040
1060
1080
c3f7ipy
65C
c3f7ipy
50C
c3f7ipy
35C
c3f7ipy
25C
c3f7ipy
15C
c3f7ipy
0C
c3f7ipy 15C
c3f7ipy 30C
0.9
1100
Neat Py
25C
4
c6f13ipy
60C
c6f13ipy
40C
c6f13ipy
25C
c6f13ipy
15C
c6f13ipy
0C
c6f13ipy
-15C
c6f13ipy
-25C
0.8
3.5
Normalized Intensity
4
3
2.5
2
1.5
1
0.5
0
900
920
940
960
980
1000
1020
Frequency (cm-1)
1040
1060
1080
0.9
1100
Neat
Thermodynamic
Conclusions
•The equilibrium constant for the 2-iodo-perflouropropane is
greater than for the 1-iodo-perfluoroalkanes.
•Mole fraction studies
•The energy of interaction (strength of the halogen bond) is
comparable across the iodo-perfluoroalkanes.
•Equal blue-shifts
•The enthalpy for complexation is smaller for the 2-iodoperfluoropropane than for the 1-iodo-perfluoroalkanes.
•Temperature studies
Thermodynamic
Conclusions
py
DhbH
DhbS
ipa
DsH
DsS
DvH
DvS
DH
py
ipa
py ipa
DS
py ipa
Thermodynamic
Conclusions
py
DhbH
DhbS
ipa
DsH
DsS
DvH
DvS
DH
py
ipa
py ipa
DS
py ipa
Thermodynamic
Conclusions
py
DhbH
DhbS
ipa
DsH
DsS
DvH
DvS
DH
py
ipa
py ipa
DS
py ipa
I’m Special !
2-iodo-perfluoropropane
1-iodo-perfluoroalkanes
Conjecture
•Stronger and more aF directed self-halogen
bonding leads to more local solvent structure
order.
•Increased positive entropy contribution
•Increased positive enthalpy contribution
One is better than two ?
One is better than two ?
Importance of the a Fluorine
Pyridine and H2H
0.1
2.5
0.2
Normalized Intensity
2
0.3
0.4
1.5
0.5
1
0.6
0.7
0.5
0.8
0
900
920
940
960
980
1000
1020
Frequency (cm-1)
1040
1060
1080
1100
0.9
Neat
Acknowledgements
•Dr. Haiyan Fan
•Dr. Mark Gealy
•Jeff Eliason
•Scott Flancher
•Diane Moliva
•Danny Green
•NSF CAREER: CHE-0341087
•Dreyfus Foundation
•Concordia Chemistry Research
Fund