Mixed cocrystal approach influences the yield for a [2+2] cycloaddition reaction within a halogen-bonded organic solid.

The synthesis, crystal structure, and [2+2] cycloaddition photoreactivity of a halogen-bonded mixed cocrystal is reported. The cocrystal solid solution contains two isosteric donors, namely, 1,4-diiodoperchlorobenzene (CICl) and iodoperchlorobenzene (CICl), along with trans-1,2-bis(pyridin-4-yl)ethylene (BPE, CHN) which behaves as a ditopic reactant molecule. The mixed cocrystal, namely, (CICl)·(CICl)·(BPE), is achieved since both halogen-bond donors are similar in shape and are interchangeable at equivalent crystallographic positions.