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Halogen Bonding. Darin J. Ulness Department of Chemistry Concordia College, Moorhead, MN. Hydrogen bonding History The s hole and s hole bonding I (2) CARS Spectroscopy Data Discussion. Outline. Hydrogen on a N, O, F Interact with a N, O, F
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Halogen Bonding Darin J. Ulness Department of Chemistry Concordia College, Moorhead, MN
Hydrogen bonding • History • The s hole and s hole bonding • I(2)CARS Spectroscopy • Data • Discussion Outline
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 Hydrogen 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
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: History
Biochemistry • Biomolecular engineering • Drug Design • Materials Science • Crystal engineering • Molecular recognition Halogen Bonding: Today 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
I Test charge close to an iodine atom The s hole 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
Electropositve s-hole The s hole Test Charge Electroneutral “ring” Electronegative “belt”
Perfluoroinate: Stronger s hole Electropositve s-hole The s hole Test Charge Electroneutral “ring” Electronegative “belt”
N N C C C C C C C C C C • The ring stretches of pyridine act as a probe of its environment Pyridine as a probe of Halogen bonding “triangle” mode “ring-breathing” mode
N C C C C C • Hydrogen bonding to a water modulates the stretching frequency Pyridine as a probe of Halogen bonding H H O N C C C C C H-bonded pyridine free pyridine
Experiment • Coherent Raman Scattering: e.g., CARS • Frequency resolved signals • Spectrograms • Molecular liquids
Spectrum One frequency (or color) frequency time Light • Electromagnetic radiation • Focus on electric field part
Time resolution on the order of the correlation time, tc Noisy Light Spectrum Frequency Noisy Light: Definition • Broadband • Phase incoherent • Quasi continuous wave
P(t) = P(1) + P(2) + P(3) … P(1) = c(1)E, P(2) = c(2)EE, P(3) = c(3)EEE Nonlinear Optics Material P= c E Signal Light field Perturbation series approximation
CARS CoherentAnti-Stokes Raman Scattering wCARS w1 w2 w1-w2= wR wCARS= w1 +wR w1 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. I(2)CARS B’ M B
I(2)CARS: Experiment Computer CCD Interferometer Monochromator t Sample B’ B M I(2)CARS Lens Broadband Source (noisy light) Narrowband Source
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
Fourier Transformation X-Marginal I(2)CARS: Data Processing
ring-breathing Pyridine as a probe of Halogen bonding H-bonded pyridine free pyridine
1-iodo-perfluoroalkanes Pyridine as a probe of Halogen bonding 2-iodo-perfluoropropane C3F7I C6F13I C4F9I
C4F9I C6F13I 1-iodo-perfluoroalkanes
C3F7I C6F13I 2-iodo-perfluoropropane
C3F7I C6F13I Temperature Studies
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
DhbH py ipa py ipa DhbS Thermodynamic Conclusions DsH DvH DsS DvS DH py py ipa DS ipa
DhbH py ipa py ipa DhbS Thermodynamic Conclusions DsH DvH DsS DvS DH py py ipa DS ipa
DhbH py ipa py ipa DhbS Thermodynamic Conclusions DsH DvH DsS DvS DH py py ipa DS ipa
2-iodo-perfluoropropane 1-iodo-perfluoroalkanes I’m Special !
Stronger and more aF directed self-halogen bonding leads to more local solvent structure order. • Increased positive entropy contribution • Increased positive enthalpy contribution Conjecture
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