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 (C6I2Cl4) and iodoperchlorobenzene (C6ICl5), along with trans‐1,2‐bis(pyridin‐4‐yl)ethylene (BPE, C12H10N2) which behaves as a ditopic reactant molecule. The mixed cocrystal, namely, (C6I2Cl4)0.75·(C6ICl5)0.25·(BPE), is achieved since both halogen‐bond donors are similar in shape and are interchangeable at equivalent crystallographic positions. The combination of I...N and Cl...N halogen bonds generates one‐dimensional chains that engage in homogeneous π‐stacks, thereby positioning a pair of reactant molecules in a suitable location to photoreact. Notably, the overall yield for the solid‐state photoreaction is influenced by the initial molar ratio of the isosteric halogen‐bond donors within the mixed cocrystal. [ABSTRACT FROM AUTHOR]