Halogen Bonding Darin J. Ulness Department of Chemistry Concordia College, Moorhead, MN.
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Halogen Bonding
Darin J. UlnessDepartment of Chemistry
Concordia College, Moorhead, MN
Outline
• Hydrogen bonding
• History
• The hole and 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
Halogen Bonding
Biochemistry• Biomolecular engineering• Drug Design
Materials Science• Crystal engineering• Molecular recognition
ComputationalChemistry
• hole bondingVoth A. R. et.al. PNAS 2007;104:6188-6193 Resnati et.al. J. Fluroine Chem.
2004;104: 271
The hole
I
Test ChargeFree Iodine
Atom
Test Charge “feels” an electroneutral field
Test charge far from an iodine atom
The hole
I
Test charge close to an iodine atom
Test Charge “feels” an electropositive field
An arbitrary spherical surface carries an eletropositive potential !
The hole
Test Charge
In molecules the electron density is directed into the bond
The hole
Electropositve-hole
Test Charge
Electroneutral“ring”
Electronegative“belt”
The hole
Electropositve-hole
Test Charge
Electroneutral“ring”
Electronegative“belt”
Perfluoroinate: Stronger hole
hole bonding with pyridine
Pyridine as a probe of Halogen bonding
The ring stretches of pyridine act as a probe of its environment
C
N
C
C C
C
C
N
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
C
N
C
C C
C
free pyridine
C
N
C
C C
C
O
HH
H-bonded pyridine
Experiment
•Coherent Raman Scattering: e.g., CARS•Frequency resolved signals•Spectrograms•Molecular liquids
Light
frequency
Spectrum
time
One frequency (or color)
Electromagnetic radiation•Focus on electric field part
Noisy Light: Definition•Broadband•Phase incoherent•Quasi continuous wave
Ele
tric
Fie
ld S
tren
gth
Time
No
isy
Lig
ht
Sp
ect
rum
Frequency
Time resolution onthe order of the correlation time, c
P= E
Nonlinear Optics
Signal
Material
Light field
Perturbation series approximation
P(t) = P(1) + P(2) + P(3) …
P(1) = (1)E, P(2) = (2)EE, P(3) = (3)EEE
CARSCoherent Anti-Stokes Raman Scattering
R
1
12
CARS
1-2= R
CARS= 1 +R
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
B’M
I(2)CARS
I(2)CARS: Experiment
Monochromator
NarrowbandSource
BroadbandSource(noisy light)
Lens
Sample
Interferometer
B
B’
MI(2)CARS
ComputerCCD
I(2)CARS: Spectrogram
Monochromator
NarrowbandSource
BroadbandSource
Lens
Sample
Interferometer
B
B’
MI(2)CARS
ComputerCCD
•Signal is dispersed onto the CCD
•Entire Spectrum is taken at each delay
•2D data set: the Spectrogram
•Vibration information
I(2)CARS: Data Processing
18000 18100 18200 18300 18400
-2
-1
0
1
2
BenzeneT22
0 200 400 600 800 1000 1200
0
25
50
75
100
125
150
BenzeneT22
100 200 300 400
0.2
0.4
0.6
0.8
Fourier
Transformation
X-Marginal
Pyridine as a probe of Halogen bonding
980 1000 1020 1040
0.0
0.2
0.4
0.6
0.8
1.0
No
rma
lize
d X
-ma
rgin
al
Wavenumber / cm-1
Pyridine as a probe of Halogen bonding
980 1000 1020 1040
0.0
0.2
0.4
0.6
0.8
1.0 100% pyr 85% pyr 70% pyr 55% pyr 25% pyr
No
rma
lize
d X
-ma
rgin
al
Wavenumber / cm-1
freepyridine
H-bondedpyridine
ring-breathing
Pyridine as a probe of Halogen bonding
C4F9I
C6F13IC3F7I
2-iodo-perfluoropropane
1-iodo-perfluoroalkanes
1-iodo-perfluoroalkanes
0
0.5
1
1.5
2
2.5
3
3.5
4
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Neat
0.1
0.2
0.3
0.4
0.5
0.6
0.7
.8
0.9
C6F13I and Pyridine
0
0.5
1
1.5
2
2.5
3
3.5
4
900 920 940 960 980 1000 1020 1040 1060 1080 1100Frequency (cm-1)
Norma
lized In
tesity
Neat
0.1
0.2
0.3
0.4
0.5
0.6
0.7
.8
0.9
C4F9I C6F13I
2-iodo-perfluoropropane
C6F13I and Pyridine
0
0.5
1
1.5
2
2.5
3
3.5
4
900 920 940 960 980 1000 1020 1040 1060 1080 1100Frequency (cm-1)
Norma
lized In
tesity
Neat
0.1
0.2
0.3
0.4
0.5
0.6
0.7
.8
0.9
C3F7I C6F13I
Pyridine and C3F7I
0
0.5
1
1.5
2
2.5
3
3.5
4
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Frequency (cm-1)
Norma
lized In
tensity
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Neat
Temperature StudiesC3F7I C6F13I
C3F7I Temp Study
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Frequency (cm-1)
Norma
lized In
tensity
c3f7ipy65Cc3f7ipy50Cc3f7ipy35Cc3f7ipy25Cc3f7ipy15Cc3f7ipy0Cc3f7ipy -15Cc3f7ipy -30C0.9
Neat Py25C
Name
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Frequency (cm-1)
Norma
lized In
tensity
c6f13ipy60Cc6f13ipy40Cc6f13ipy25Cc6f13ipy15Cc6f13ipy0Cc6f13ipy-15Cc6f13ipy-25C0.8
0.9
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-iodo-perfluoropropane than for the 1-iodo-perfluoroalkanes.
•Temperature studies
Thermodynamic Conclusions
H
S
py
py py
pyipa
ipa ipa
ipa
vH
vS
sH
sS
hbH
hbS
Thermodynamic Conclusions
H
S
py
py py
pyipa
ipa ipa
ipa
vH
vS
sH
sS
hbH
hbS
Thermodynamic Conclusions
H
S
py
py py
pyipa
ipa ipa
ipa
vH
vS
sH
sS
hbH
hbS
I’m Special !
2-iodo-perfluoropropane 1-iodo-perfluoroalkanes
Conjecture
•Stronger and more F 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 Fluorine
Pyridine and H2H
0
0.5
1
1.5
2
2.5
900 920 940 960 980 1000 1020 1040 1060 1080 1100
Frequency (cm-1)
Norma
lized In
tensity
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
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
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