Copper(I) coordination polymers of N,N'-bis[3-(methylthio)propyl]pyromellitic diimide: crystal transformation and solvatochromism by halogen-π interactions.

Four copper(I) coordination polymers with ligand N,N'-bis[3-(methylthio)propyl]pyromellitic diimide (L), [Cu(2)I(2)L(2)](n) (1), [Cu(2)I(2)L(2)](n) (2), [Cu(2)I(2)L](n) (3), and {[Cu(2)I(2)L(2)]·CH(2)Cl(2)}(n) (4), have been successfully synthesized and structurally characterized by single-crystal X-ray diffraction. Structural transformations between the polymers were controlled by the appropriate solvent composition, mole ratio, or temperature. When a 1:1 CuI/L ratio was employed, dimorphic products, 1 and 2, based on a rhomboid Cu(2)I(2) cluster were obtained from an acetonitrile solution and from a dichloromethane/acetonitrile solution with ultrasonication, respectively. When a 1:2 CuI/L ratio was employed, polymer 3 based on infinite stair-step polymer (CuI)(∞) was crystallized. Crystalline product 4 was obtained by the transformation of 1 in a mixed-solvent system with a 1:5 acetonitrile/dichloromethane ratio. Polymers 1-4 were transformed into polymer 3 at 197 °C. X-ray structures of 2-4 show short distances (3.406-3.667 Å) between halogens (I(-) and Cl) and aromatic rings. 1 and 4 show solvatochromism; upon inclusion of the colorless electron donor CH(2)Cl(2), the red color changes as a result of the formation of a chloride-π charge-transfer complex 4 of a pale-colored electron acceptor, 1. Therefore, the origin of the red color from 2 and 3 is also assigned as iodide-to-electron-deficient aromatic π charge transfer.