Photochromism of novel metal coordination polymers with 1,2-bis(2′-methyl-5′-(carboxylic acid)-3′-thienyl)perfluorocyclopentene in the crystalline phase

Three new metal complexes with 1,2-bis(2'-methyl-5'-(carboxylic acid)-3'-thienyl)perfluorocyclopentene (BM-5-CATP) were synthesized and characterized by X-ray diffraction analysis. BM-5-CATP serves as a bis-monodentate ligand that bridges metal centers to generate three 1D polymers. The two thienyl rings in the three complexes adopt antiparallel fashions, and the distances of 3.39, 3.53, and 3.57 angstrom between the two reactive carbons are short enough to allow photocyclizations to occur in the crystalline phase. [Co(BM-5-CATP)(py)(2)(MeOH)(2)] (1) displayed effective photoisomerization in the crystalline phase. Interestingly, solvated 1 underwent a solid-state conversion upon heating to generate, through the release of the coordinated MeOH and rearrangement of the coordination geometry, the desolvated form (1a), while maintaining reversible photochromism. The removal of the solvent led to obvious changes in physical properties such as color and magnetic properties. The ESR spectra of 1 and 1a changed reversibly upon photoexcitation, indicating changes in coordination geometry accompanied by photoreaction. The magnetic susceptibilities of 1 and 1a showed no obvious changes, suggesting that the cobalt-cobalt interaction through the long bridging BM-5-CATP is less effective. Both [Cu(BM-5-CATP)(py)(3)](EtOH)(py)(1.8) (2) and [Zn(BM-5-CATP)(phen)(H2O)] (3) exhibited reversible photoreactions in the crystalline phase. However, 3 did not show remarkable spectral changes because of steric hindrance from the coordinated bulky phenanthroline and the intramolecular H bonds.