New structurally diverse photoactive cadmium coordination polymers

Abstract

Four structurally diverse coordination polymers 1–4 (CP₁–CP₄) were designed and constructed from Cd(II) ions and various carboxyl ligands (H₂oba, 4,4′-oxydibenzoic acid; H₂bpa, (E)-4,4′-(ethene-1,2-diyl)dibenzoic acid; H₂pbda, 4,4′-((1,3-phenylenebis(methylene))bis(oxy))dibenzoic acid) and the alkene containing ligand (CH₃-bpeb, 4,4′-((1E,1′E)-(2,5-dimethyl-1,4-phenylene)bis(ethene-2,1-diyl))dipyridine). CP₁–CP₄ possess Cd₂ binuclear secondary building units (SBUs). The geometry of the dicarboxylate ligands and the reaction conditions determined the final structure with a variety of motifs. CP₁ possesses an interdigitated 2D structure, while CP₂ consists of a 1D channel-like motif with isolated CH₃-bpeb molecules embedded in the channels. The solid-state structure of CP₃ consists of two unique layers interpenetrated to form a 2D + 2D → 2D polycatenated backbone, while a 1D channel-like motif filled by isolated CH₃-bpeb molecules was observed for CP₄. In all four coordination polymers pairs of CH₃-bpeb molecules were bound or encapsulated by the Cd₂ secondary building units at an appropriate distance and orientation for solid-state [2 + 2] photodimerization of one pair of CC bonds. Desolvation of CP₃ with heat resulted in a decrease in solid-state fluorescence and a slowing of the rate of solid-state photodimerization.