The ability of 1,2,4,5-tetrachloro-3-iodobenzene to act as a template to form a pair of polymorphic cocrystals with trans-1,2-bis(4-pyridyl)ethylene is reported. After exposure to ultraviolet light, a nearly quantitative yield for the [2 + 2] cycloaddition reaction was observed for both concomitant cocrystals. These crystalline solids engage in both I center dot center dot center dot N halogen bonds along with nontraditional C-H center dot center dot center dot N hydrogen bond which results in a one-dimensional chain. In addition, the components homogeneous pi-pi stack which positions the carbon-carbon double bond on the reactant molecule in a suitable orientation to undergo a photoinduced cyclization reaction.

The formation of a series of isostructural three-component co-crystals between 1,2,4,5-tetrachloro-3-iodobenzene and each of three isosteric bipyridines is reported.

The formation, structure, and photoreactivity of a pair of silver(I) complexes based upon either trifluoromethanesulfonate [Ag(CF3SO3)] or p-toluenesulfonate [Ag(C7H7SO3)] anions along with the ester-based reactant molecule trans-1-(4-methylbenzoate)-2-(4-pyridyl)ethylene (1) are reported. In both complexes, silver(I) ions form coordinated covalent bonds to the 4-pyridyl group on the olefin containing reactant molecule and due to either argentophilic interactions or close packing of a pair of silver(I) ions ultimately places a pair of carbon-carbon bonds (C = C) on neighboring molecules of 1 in a suitable position to undergo a solid-state [2 + 2] cycloaddition reaction. In particular, the complexes [Ag(CF3SO3)(1)(2)]center dot CH3CN and [Ag-2(C7H7SO3)(2)(1)(4)] both undergo a quantitative photoreaction to yield the head-to-head photoproduct rctt-1,2-bis(4-methylbenzoate)-3,4-bis(4-pyridyl)cyclobutane (2) upon exposure to ultraviolet light.

Structural diversity is achieved in a series of halogen-bonded co-crystals based upon cooperative non-covalent interactions and the synthetic feed of the components.