Introduction

There has recently been an increasing interest in halogen bonds, XBs, because of their unique properties and their tremendous potential in the fields of molecular recognition, crystal engineering, supramolecular chemistry and the development of new pharmaceutical compounds. The study of the nature of halogen bonding interactions has turned out to be an important aspect of this topic. Studies of the electrostatic potentials of halogen-containing molecules show that the atoms of a halogen covalently bound often have a region of positive electrostatic potential on the outermost portion of the halogen atom, centered on the extension of the D−X bond [1–4]. Politzer et al. have attributed the formation of halogen bonds to the attractive electrostatic interaction between this positive potential and a lone pair of the acceptor. The presence of a region with positive electrostatic potential on a halogen indicates that noncovalent interactions between that halogen and a Lewis base should be highly electrostatic in nature.