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

Abstract

Abstract 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 Δ E BSSE,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. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006