Construction of Coordination Polymers with a Bifurcating Ligand: Synthesis, Structure, Photoluminescence, and Magnetic Studies

A new ligand, 3,5-di(1H-imidazol-1-yl)benzonitrile (DICN), has been synthesized by reacting 3,5-difluor-obenzonitrile 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] center dot H2O}(n) (1), {[Zn(DIBA)(MeCOO)] center dot H2O}(n) (2 center dot H2O), {[Zn(DIBA)(NO3)]}(n) (3), {[Cu(DIBA)] center dot H2O}(n) (4), {[Ni(DIBA)(2)(H2O)(2)] center dot 3H(2)O}(n) (5), {[Co(DIBA)-(OH)] center dot H2O}(n) (6), and {[Pb-2(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 center dot 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 center dot 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.