Halogen Bonding

1
Halogen Bonding
Darin J. Ulness Department of Chemistry Concordia
College, Moorhead, MN
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Outline

• Hydrogen bonding
• History
• The s hole and s hole bonding
• I(2)CARS Spectroscopy
• Data
• Discussion

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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

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Halogen Bonding

• I gt Br gt Cl, no F
• Interact with a N, O
• Bond distance shorter than sum of Van der Waals
  Radii
• Angle approximately 180o

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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

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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 20071046188-6193
Resnati et.al. J. Fluroine Chem. 2004104 271
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The s hole
Test charge far from an iodine atom
I
Test Charge
Free Iodine Atom
Test Charge feels an electroneutral field
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The s hole
Test charge close to an iodine atom
Test Charge feels an electropositive field An
arbitrary spherical surface carries an
eletropositive potential !
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The s hole
Test Charge
In molecules the electron density is directed
into the bond
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The s hole
Electropositve s-hole
Test Charge
Electroneutral ring
Electronegative belt
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The s hole
Perfluoroinate Stronger s hole
Electropositve s-hole
Test Charge
Electroneutral ring
Electronegative belt
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s hole bonding with pyridine
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Pyridine as a probe of Halogen bonding
The ring stretches of pyridine act as a probe of
its environment
triangle mode
ring-breathing mode
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Pyridine as a probe of Halogen bonding
Hydrogen bonding to a water modulates the
stretching frequency
H
H
O
N
C
C
C
C
C
H-bonded pyridine
free pyridine
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Experiment

• Coherent Raman Scattering e.g., CARS
• Frequency resolved signals
• Spectrograms
• Molecular liquids

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Light

• Electromagnetic radiation
• Focus on electric field part

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Noisy Light Definition

• Broadband
• Phase incoherent
• Quasi continuous wave

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Nonlinear Optics
Material
P c E
Signal
Light field
Perturbation series approximation
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CARS
Coherent Anti-Stokes Raman Scattering
wCARS
w1
w2
w1-w2 wR wCARS w1 wR
w1
wR
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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.

I(2)CARS
B
M
B
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I(2)CARS Experiment
Computer
CCD
Interferometer
Monochromator
t
Sample
B
B
M
I(2)CARS
Lens
Broadband Source (noisy light)
Narrowband Source
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I(2)CARS Spectrogram
Computer
CCD
Interferometer
Monochromator
t
Sample
B
B
I(2)CARS
M
Lens
Broadband Source
Narrowband Source

• Signal is dispersed onto the CCD
• Entire Spectrum is taken at each delay
• 2D data set the Spectrogram
• Vibration information

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I(2)CARS Data Processing
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Pyridine as a probe of Halogen bonding
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Pyridine as a probe of Halogen bonding
ring-breathing
H-bonded pyridine
free pyridine
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Pyridine as a probe of Halogen bonding
1-iodo-perfluoroalkanes
2-iodo-perfluoropropane
C3F7I
C6F13I
C4F9I
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1-iodo-perfluoroalkanes
C4F9I
C6F13I
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2-iodo-perfluoropropane
C3F7I
C6F13I
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Temperature Studies
C3F7I
C6F13I
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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

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Thermodynamic Conclusions
DhbH?
py
py
ipa
ipa
DhbS?
DsH?
DvH?
DsS?
DvS?
DH?
py
py
ipa
DS?
ipa
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Thermodynamic Conclusions
DhbH?
py
py
ipa
ipa
DhbS?
DsH?
DvH?
DsS?
DvS?
DH?
py
py
ipa
DS?
ipa
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Thermodynamic Conclusions
DhbH?
py
py
ipa
ipa
DhbS?
DsH?
DvH?
DsS?
DvS?
DH?
py
py
ipa
DS?
ipa
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Im Special !
2-iodo-perfluoropropane
1-iodo-perfluoroalkanes
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Conjecture

• Stronger and more aF directed self-halogen
  bonding leads to more local solvent structure
  order.
• Increased positive entropy contribution
• Increased positive enthalpy contribution

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One is better than two ?
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One is better than two ?
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Importance of the a Fluorine
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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