Construction of coordination polymers with a bifurcating ligand: synthesis, structure, photoluminescence, and magnetic studies

Abstract

A new ligand, 3,5-di(1H-imidazol-1-yl)benzonitrile (DICN), has been synthesized by reacting 3,5-difluorobenzonitrile with imidazole in good yields. The cyanide group hydrolyzes to carboxylic acid under solvothermal conditions in the presence of different metal salts giving rise to carboxylate and imidazole bonded coordination polymers. Seven such polymers, {[Cd(DIBA)I]·H₂O}_n (1), {[Zn(DIBA)(MeCOO)]·H₂O}_n (2·H₂O), {[Zn(DIBA)(NO₃)]}_n (3), {[Cu(DIBA)]·H₂O}_n (4), {[Ni(DIBA)₂(H₂O)₂]·3H₂O}_n (5), {[Co(DIBA)(OH)]·H₂O}_n (6), and {[Pb₂(DIBA)(OH)(NO₃)]}_n (7) (DIBA⁻ = 3,5-di(1H-imidazol-1-yl)benzoate)), have been isolated. These polymers have been structurally characterized by single crystal X-ray diffraction, thermogravimetric (TGA), and elemental analysis. Both 1 and 2·H₂O form honeycomb two-dimensional (2D) layer structures that stack on top of one another to form three-dimensional (3D) networks. 3 and 6 have the same (2,4,6) connected net, while 4 is a rare 3-connected net with a 3D network. Compounds 5 and 7 have one-dimensional (1D) and zigzag 2D polymeric structures, respectively. 2·H₂O exhibits dynamic behavior through sliding of the 2D layers upon removal of solvent molecules in a single-crystal to single-crystal (SC-SC) fashion. The Zn²⁺ and Cd²⁺ coordination polymers exhibit solid-state luminescence at RT. Variable temperature (2-300 K) magnetic susceptibility data on 5 are consistent with a weak ferromagnetically coupled 1D chain of Ni²⁺ ions. For 6, a spin-glass behavior with slow relaxation and frustration is inferred from the susceptibility data.