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

Abstract

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 3.90Å whereas the other is a photo-inactive parallel conformation in which the reactive C-C distance is 4.42Å. 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 (λ=254nm) and visible light (λ>550nm).Reaction of CoCl2·6H2O 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 3.80Å 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 photochromism from metal coordination and extensive H bonds as well as Van de Waals contacts. The λmax of 1 (580nm) in closed form shifted to longer wavelength compared with that of free ligand (576nm).