Hydrogen bonds between hydrogen fluoride and aromatic azines: An ab initio study

摘要

MP2/6-31 + +G(d,p) ab initio molecular orbital calculations have been employed to characterize hydrogen-bonded complexes between hydrogen fluoride as proton donor and aromatic azines (pyridine, pyrimidine, pyridazine, pyrazine, 1,3,5-triazine, and 1,2,4-triazine). Our calculations have shown that the H-bond strength in these complexes depends on both the number of nitrogen atoms as well as the position of these atoms in aromatic ring. The binding energies of azines-HF with or without BSSE and ZPE corrections decrease with the increasing number of nitrogen atoms in the ring. For example, its Delta E-BSSE,E-ZPE value is 40.9 kJ . mol(-1) in pyridine-HF, whereas its corresponding values in pyrazine-HF and 1,3,5-triazine-HF are 34.0 kJ . mol(-1) and 26.6 kJ . mol(-1), respectively. With respect to position of the nitrogen atom in the aromatic ring, the more pronounced effect is verified when it is at meta-position relative to the pyridine ring. There is a high linear correlation between the H-bond strength in these complexes and the intermolecular charge transfer using corrected Mulliken charges obtained from the charge-charge flux-overlap (CCFO) modified model for infrared intensities. Finally, our MP2/6-31 + +G(d,p) calculations have revealed that stronger hydrogen bonds are associated with smaller H-bond length values, larger intermolecular charge transfers and greater H-F downward stretching frequency displacements. (C) 2006 Wiley Periodicals, Inc.