Preference of halogen bonds over hydrogen bonds within a discrete three-component co-crystal that undergo a [2+2] cycloaddition reaction

Abstract

The formation of a series of isostructural three-component co-crystals between 1,2,4,5-tetrachloro-3-iodobenzene (C₆HICl₄) and each of three isosteric bipyridines is reported. Even though C₆HICl₄ is capable of forming both halogen and hydrogen bonds the donor is found to form co-crystals with only I⋯N halogen bonds when the initial ratio of the molecular components is 2 : 1. Molecules of C₆HICl₄ stack in a homogeneous and face-to-face configuration which aligns the bipyridine-based acceptor molecule in a similar π-stacked orientation. As a result, the co-crystal containing trans-1,2-bis(4-pyridyl)ethylene undergoes a nearly quantitative [2+2] cycloaddition reaction in the solid state.