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Halogen Bonding

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

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

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

  3. 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

  4. 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

  5. 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

  6. 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

  7. The s hole Test charge far from an iodine atom I Test Charge Free Iodine Atom Test Charge “feels” an electroneutral field

  8. 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 !

  9. The s hole Test Charge In molecules the electron density is directed into the bond

  10. Electropositve s-hole The s hole Test Charge Electroneutral “ring” Electronegative “belt”

  11. Perfluoroinate: Stronger s hole Electropositve s-hole The s hole Test Charge Electroneutral “ring” Electronegative “belt”

  12. s hole bonding with pyridine

  13. 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

  14. 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

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

  16. Spectrum One frequency (or color) frequency time Light • Electromagnetic radiation • Focus on electric field part

  17. Time resolution on the order of the correlation time, tc Noisy Light Spectrum Frequency Noisy Light: Definition • Broadband • Phase incoherent • Quasi continuous wave

  18. 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

  19. CARS CoherentAnti-Stokes Raman Scattering wCARS w1 w2 w1-w2= wR wCARS= w1 +wR w1 wR

  20. 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

  21. I(2)CARS: Experiment Computer CCD Interferometer Monochromator t Sample B’ B M I(2)CARS Lens Broadband Source (noisy light) Narrowband Source

  22. 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

  23. Fourier Transformation X-Marginal I(2)CARS: Data Processing

  24. Pyridine as a probe of Halogen bonding

  25. ring-breathing Pyridine as a probe of Halogen bonding H-bonded pyridine free pyridine

  26. 1-iodo-perfluoroalkanes Pyridine as a probe of Halogen bonding 2-iodo-perfluoropropane C3F7I C6F13I C4F9I

  27. C4F9I C6F13I 1-iodo-perfluoroalkanes

  28. C3F7I C6F13I 2-iodo-perfluoropropane

  29. C3F7I C6F13I Temperature Studies

  30. 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

  31. DhbH py ipa py ipa DhbS Thermodynamic Conclusions DsH DvH DsS DvS DH py py ipa DS ipa

  32. DhbH py ipa py ipa DhbS Thermodynamic Conclusions DsH DvH DsS DvS DH py py ipa DS ipa

  33. DhbH py ipa py ipa DhbS Thermodynamic Conclusions DsH DvH DsS DvS DH py py ipa DS ipa

  34. 2-iodo-perfluoropropane 1-iodo-perfluoroalkanes I’m Special !

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

  36. One is better than two ?

  37. One is better than two ?

  38. Importance of the a Fluorine

  39. 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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