Structural Transformation of Photoreactive Helical Coordination Polymers to Two-Dimensional Structures

Abstract

Four helical one-dimensional coordination polymers (CPs) have been synthesized using trans-5-styrylpyrimidine (5-Spym), triphenylphosphine, and silver(I) salts of NO3– (1), BF4– (2), ClO4– (3), and F3CCO2– (4) anions. The styryl group attached to the pyrimidine ligand makes all the helical CPs photoreactive. The helical chains are aligned in parallel in the solid state such that the 5-Spym arms of the adjacent helical chains are juxtaposed in a head-to-tail manner readily to undergo [2 + 2] photo-cycloaddition reaction. The loss of guest solvents in the solids during the photoreaction prevents the single-crystal-to-single-crystal reaction. However, all four helical chains undergo [2 + 2] cycloaddition under UV light quantitatively to two-dimensional (2D) coordination polymers. The photodimer obtained from the nitrate salt (1) was recrystallized for single crystal X-ray crystallography to confirm the photoproduct (5) structurally. Compound 5 has the 2D coordination polymeric structure comprising helical rods connecting the cyclobutane rings to form a honeycomb topology.