American Chemical Society
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Copper(I) Coordination Polymers of N,N′-Bis[3-(methylthio)propyl]pyromellitic Diimide: Crystal Transformation and Solvatochromism by Halogen−π Interactions

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journal contribution
posted on 2011-02-07, 00:00 authored by Garam Park, Hojin Yang, Tae Ho Kim, Jineun Kim
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 14 were transformed into polymer 3 at 197 °C. X-ray structures of 24 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.