Photochromic 1,2-bis(2'-methyl-5'-(carboxylic acid)-3'-thienyl) perfluorocyclopentene and its Co(II) coordination polymer

Crystallization from methanol of 1,2-bis(2'-methyl-5'-(carboxylic acid)-3'-thienyl) perfluorocyclopentene (BM-5-CATP, H2L) afforded a new single crystal (H2LMeOH) characterized by single crystal X-ray diffraction analysis, whose structure is different from those of the known crystals crystallized from ethanol, acetone/ hexane or acetonitrile. There are two independent molecules with different conformations in one asymmetric unit of H2L. One is a photo-active anti-parallel conformation in which the reactive C atoms are separated by 3.90 angstrom whereas the other is a photo-inactive parallel conformation in which the reactive C-C distance is 4.42 angstrom. The packing characteristics of the two structures derived from methanol and ethanol were compared and analyzed in detail helped by the corresponding computational analyses. The photo-isomerizations of H2LMeOH in tetrahydrofuran and in solid state occur reversibly upon alternate irradiation with ultraviolet (lambda = 254 nm) and visible light (lambda > 550 nm). Reaction of CoCl2 .6H(2)O with BM-5-CATP in methanol afforded a new complex [CoL(MeOH)(4)](MeOH) (1). Complex 1 is revealed by X-ray crystal diffraction as a 1D zigzag chain, where BM-5-CATP serves as bis-monodentate ligand bridging Co(II) centers in syn-anti fashion. The two thienyl rings in 1 adopt anti-parallel fashions and the distances of 3.80 angstrom between two reactive carbons is short enough for the occurrence of photocyclizations. As expect, complex 1 displayed effective photo-isomerization in crystalline phase with color interconversion between pink and purple, indicating weak suppression of photo-chromism from metal coordination and extensive H bonds as well as Van de Waals contacts. The lambda(max) of 1 (580 nm) in closed form shifted to longer wavelength compared with that of free ligand (576 nm). (C) 2017 Elsevier B.V. All rights reserved.