Theoretical Study Of Linear Halogen Bonding And Effects Of Halogen Bonding On The Ring Stretching Modes Of Pyridine

In this paper, we employed ab initio (Ab initio) method to study the formation of halogen bonds between H2O, H2S and dihalogen molecules, electronic properties of the halogen bonds Z3CX…Y- between halide anions and methyl halides, halogen bonds between pyridine and halomethanes. At the same time, we analysed the effect of intermolecular halogen bond towards carbon-halogen bond and four pyridine ring regular vibration modes. And we systematicly discussed the essence of pyridine ring vibration frequency blue shift. The main contents include the following three parts:1. Ab initio quantum chemistry methods were employed to investigate the formation of linear halogen bonds O(S)…X-Y between H2O, H2S and dihalogen molecules. The calculation results demonstrated that the formation of the halogen bonds leads to an increase in the X-Y bond length and a red shift in its frequency in all complexes. Topological analysis of electron density indicated that the halogen bond interaction in the complexes was the closed shell interaction. Natural bond orbital (NBO) analysis displayed that the frequency red shift of X-Y bond was the result of the intermolecular charge transfer caused by the intermolecular hyperconjugation n(O, S)â†'σ*(X-Y).2. The linear halogen bonds Z3CX...Y- (X= Cl, Br; Y, Z= F, Cl, Br) are theoretically investigated by using five different kinds of calculational level. They have large interaction energies,23～160 kJ/mol, and are closed-shell interactions. In some systems a blue-shifted halogen bond is formed. Although the electrostatic interaction is important, the intermolecular charge transfer caused by the intermolecular hyperconjugation n(Y-)â†'σ*(CX) and the intramolecular charge redistribution by the intramolecular hyperconjugation n(Z)â†'σ*(CX) play important roles in the formation of the halogen bonds.3. Ab initio quantum chemistry MP2 and density functional method (B3LYP) methods plus the AUG-cc-pVDZ, AUG-cc-pVTZ,6-311++G(d, p) and 6-311++G(2df, 2p) basis sets were employed to investigate pyridines involved in the N...X-C halogen bonds with halomethanes (F3CCl, F3CBr, Cl3CCl, Cl3CBr, Br3CCl, Br3CBr). We explored that the formation of halogen bond has effect on pyridine ring stretching vibration frequency, the essence of pyridine ring vibration frequency blue shift and charge transfer leads to shift of pyridine ring stretching vibration frequency. The results demonstrated that the formation of halogen bond leads to blue shift in the frequencies of the ring breathing mode vi, the N-para-C stretching mode v6a and the meta-CC stretching mode v8a. The natural bond orbital(NBO) analysis shows that the frequency blue shift in the ring stretching modes of pyridine is a corporate result of the intermolecular charge transfer caused by the intermolecular hyperconjugation n(N)â†'σ*(X-C) and the intramolecular charge redistribution caused by intramolecular hyperconjugation n(N)â†'σ*(meta-CC) in the pyridine ring. We also found that the magnitude of the frequency blue shift increases with the strength of the hydrogen bonding.