Theoretical investigation on charge-assisted halogen bonding interactions in the complexes of bromocarbons with some anions

A series of dimeric complexes formed between bromocarbon molecules and two anions (Br^- and CN^-) have been investigated by using MP2 method. The quantum theory of atoms in molecules (QTAIM) and the second-order perturbation natural bond orbital (NBO) approaches were applied to analyze the electron density distributions of these complexes and to explore the nature of charge-assisted halogen bonding interactions. As anticipated, these interactions are significantly stronger relative to the corresponding neutral ones. The results derived from ab initio calculations described herein reveal a major contribution from the electrostatic interaction on the stability of the systems considered. Beside the electrostatic interaction, the charge-transfer force and the second-order orbital interaction also play an important role in the formation of the complexes, as a NBO analysis suggested. The presence of halogen bonds in the complexes has been identified in terms of the QTAIM methodology, and several linear relationships have been established to provide more insight into charge-assisted halogen bonding interactions.