Structural Transformation of Photoreactive Helical\nCoordination Polymers to Two-Dimensional Structures

Abstract

Four helical one-dimensional coordination\npolymers (CPs) have been\nsynthesized using <i>trans</i>-5-styrylpyrimidine (5-Spym),\ntriphenylphosphine, and silver­(I) salts of NO₃^– (<b>1</b>), BF₄^– (<b>2</b>), ClO₄^– (<b>3</b>), and F₃CCO₂^– (<b>4</b>) anions.\nThe styryl group attached to the pyrimidine ligand makes all the helical\nCPs photoreactive. The helical chains are aligned in parallel in the\nsolid state such that the 5-Spym arms of the adjacent helical chains\nare juxtaposed in a head-to-tail manner readily to undergo [2 + 2]\nphoto-cycloaddition reaction. The loss of guest solvents in the solids\nduring the photoreaction prevents the single-crystal-to-single-crystal\nreaction. However, all four helical chains undergo [2 + 2] cycloaddition\nunder UV light quantitatively to two-dimensional (2D) coordination\npolymers. The photodimer obtained from the nitrate salt (<b>1</b>) was recrystallized for single crystal X-ray crystallography to\nconfirm the photoproduct (<b>5</b>) structurally. Compound <b>5</b> has the 2D coordination polymeric structure comprising helical\nrods connecting the cyclobutane rings to form a honeycomb topology.