A quantitative insight into the 'amphiphilicity' of covalently-bonded halogens from ab initio calculations

A series of complexes formed between bromine-containing molecules RBr and HF have been investigated at the MP2(full)/aug-cc-pvdz level of theory. This, together with a previous work [J.W. Zou, Y.J. Jiang, M. Guo, G.X. Hu, B. Zhang, H.C. Liu, Q.S. Yu, Chem. Eur. J. 11 (2005) 740] on the halogen-bonded RBr⋯NH₃ complexes, offers a quantitative insight into the nucleophile 'head on' and electrophile 'side on' interactions of halogens. It has been shown that the stronger electron-withdrawing ability of the moiety bound to the bromine is, the weaker is the Br⋯H interaction to which it gives rise, which is contrary to the trend probed in the RBr⋯NH₃ complexes. Several linear relationships have been established to provide further understanding of the 'amphiphilicity' of covalently-bonded halogens. The topological parameters obtained in terms of Bader's atoms in molecules (AIM) theory have also been applied for the analysis of these Br⋯H interactions.