Exploring the role of substituents on cooperativity between N⋯HF and CH⋯F hydrogen bonds in ternary systems involving aromatic azine: Substituted complexes of s-triazine:HF:s-triazine as a working model

Abstract

In order to investigate the influence of substituents on cooperativity between N⋯HF and CH⋯F hydrogen bonds, a number of para- and meta-substituted s-triazine respectively in X′-s-triazine:HF:s-triazine and s-triazine:HF:s-triazine-X2 complexes are chosen (X or X′=H, F, Cl, Br, CN, NH2, NO2, CH3 and N(CH3)2). Here, the cooperative effects on energetic, geometrical and topological properties are examined at the MP2/6-311++G(d,p) level. Unlike di-substituted complexes, the mono-substituted ones involving electron donating substituents are more stable and therefore preferable. A cooperativity is observed between N⋯HF and CH⋯F hydrogen bonds in the ternary complexes. In other words, these interactions in the ternary complexes work in concert with each other and enhance each other’s strength. The favorable influences of N⋯HF and CH⋯F hydrogen bonds on each other are also confirmed by the results of natural bond orbital (NBO) and atoms in molecules (AIM) analyses. The results indicate that substituent effects on cooperativity between N⋯HF and CH⋯F hydrogen bonds can be expressed by Hammett constants.