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

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Presentation on theme: "Halogen Bonding Darin J. Ulness Department of Chemistry Concordia College, Moorhead, MN."— Presentation transcript:

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

2 Outline Hydrogen bonding History The  hole and  hole bonding I (2) CARS Spectroscopy Data Discussion

3 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 180 o

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

5 Halogen Bonding: History F. Guthrie, J. Chem. Soc. 16, 239 (1863) Complexation of I 2 and NH 3 I. Remsen, J.F. Norris, Am. Chem. J. 18, 90, (1896) Complexation of X 2 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

6 Halogen Bonding: Today Halogen Bonding Biochemistry Biomolecular engineering Drug Design Materials Science Crystal engineering Molecular recognition Computational Chemistry  hole bonding Voth A. R. et.al. PNAS 2007;104: Resnati et.al. J. Fluroine Chem. 2004;104: 271

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

8 The  hole I Test charge close to an iodine atom Test Charge “feels” an electropositive field An arbitrary spherical surface carries an eletropositive potential !

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

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

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

12  hole bonding with pyridine

13 Pyridine as a probe of Halogen bonding The ring stretches of pyridine act as a probe of its environment C N C CC C C N C CC C “ring-breathing” mode “triangle” mode

14 Pyridine as a probe of Halogen bonding Hydrogen bonding to a water modulates the stretching frequency C N C CC C free pyridine C N C CC C O H H H-bonded pyridine

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

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

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

18 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

19 CARS Coherent Anti-Stokes Raman Scattering RR 11 11 22  CARS  1 -  2 =  R  CARS =  1 +  R

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. B B’ M I (2) CARS

21 I (2) CARS: Experiment Monochromator Narrowband Source Broadband Source (noisy light) Lens Sample Interferometer  B B’ M I (2) CARS Computer CCD

22 I (2) CARS: Spectrogram Monochromator Narrowband Source Broadband Source Lens Sample Interferometer  B B’ M I (2) CARS Computer CCD Signal is dispersed onto the CCD Entire Spectrum is taken at each delay 2D data set: the Spectrogram Vibration information

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

24 Pyridine as a probe of Halogen bonding

25 free pyridine H-bonded pyridine ring-breathing

26 Pyridine as a probe of Halogen bonding C4F9IC4F9I C 6 F 13 I C3F7IC3F7I 2-iodo-perfluoropropane 1-iodo-perfluoroalkanes

27 C4F9IC4F9IC 6 F 13 I

28 2-iodo-perfluoropropane C3F7IC3F7IC 6 F 13 I

29 Temperature Studies C3F7IC3F7IC 6 F 13 I

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 Thermodynamic Conclusions HH SS py ipa vHvH vSvS sHsH sSsS  hb H   hb S 

32 Thermodynamic Conclusions HH SS py ipa vHvH vSvS sHsH sSsS  hb H   hb S 

33 Thermodynamic Conclusions HH SS py ipa vHvH vSvS sHsH sSsS  hb H   hb S 

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

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

36 One is better than two ?

37

38 Importance of the  Fluorine

39 Acknowledgements Dr. Haiyan Fan Dr. Mark Gealy Jeff Eliason Scott Flancher Diane Moliva Danny Green NSF CAREER: CHE Dreyfus Foundation Concordia Chemistry Research Fund


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