Seven new Zn(II)/Cd(II) coordination polymers with 2-(hydroxymethyl)-1H-benzo[d]imidazole-5-carboxylic acid: Synthesis, structures and properties

Using a new simi-rigid multitopic ligand 2-(hydroxymethyl)-1H-benzo[d]limidazole-5-carboxylic acid (H2L), seven new coordination polymers [Zn-3(L)(2)(mu(2)-OH)(2)](n) (1), {[Zn-2(HL)(2)(H2O)(2)]center dot SiF6}(n) (2), [Zn(HL)(SCN)](n) (3), {[Zn-2(HL)(2)(SO4)]center dot(4,4'-bpy)}(n), (4) [4,4'-bpy {[Zn-2(HL)(2)]center dot 2H(2)O}(n) (5), {[Cd(HL)(2)]center dot 2H(2)O}(n) (6) and [Cd-2(HL)(2)(H2O)(2)(SO4)](n) (7) have been successfully obtained from H2L ligand under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, powder X-ray diffraction and IR spectroscopy. In addition, UV-vis diffuse-reflectance spectra demonstrate wide band gaps. Complex 1 features a 3D topological net of {4(12).6(3)} with the stoichiometry (6-c), contains 1D channels with the accessible solvent volume of 42.1%. 3, 4, 5 and 6 have a 1D chain structure, 5 and 6 further assemble to form 2D sheet and 3D supramolecular frameworks by hydrogen-bonding interactions, respectively. Complexes 2 and 7 possess a 2D layered structure, and the 2D supramolecular network of 2 can be rationalized to be four-connected {4(4).6(2)} topological sql network with the dinuclear units, while 7 shows a 3-nodal 2D net with a point symbol of {6(3)}. Moreover, the fluorescent emission, fluorescence lifetimes of 1-7 have been investigated and discussed. Interesting enough, complex 1 showed high efficiency for catalyzing the Knoevenagel condensation reaction between 4-substituted aromatic aldehydes and malononitrile as selective heterogeneous catalyst. The CPs combining catalytic and fluorescent properties could further meet the requirement as a multifunctional material.