Two supramolecular isomers with different structural features: reversible transformation and fluorescence properties

Two supramolecular isomers, {[Cd2(pda)2(1,10′-phen)2]·H2O}n (1) and {[Cd2(pda)2(1,10′-phen)2]·4H2O}n (2) (1,10′-phen = 1,10-phenanthroline, pda = phenylenediacrylate dianion), have been synthesized and characterized by single-crystal X-ray analysis. Complex 1 exhibits a 3D network constructed from 1D rod-shaped secondary building units, while 2 shows a 3D, twofold interpenetrated framework. There exists a reversible transformation between the pair of isomers: when yellow block crystals of 1 are treated under microwave irradiation, colorless plate crystals of 2 are formed; in turn, if crystals of 2 are dissolved in water and left undisturbed about two weeks at room temperature, crystals of 1 reappear. Fluorescence properties of 1 and 2 have also been studied.