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), [Cu₂I₂L₂]_n (1), [Cu₂I₂L₂]_n (2), [Cu₂I₂L]_n (3), and {[Cu₂I₂L₂]·CH₂Cl₂}_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 Cu₂I₂ 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 CH₂Cl₂, 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.