Synthesis, structures and luminescence of three coordination polymers constructed from rigid 1,3,5-benzenetricarboxylic acid and flexible bis(imidazol-1-ylmethyl)-benzene

Three coordination polymers, [Cd-3(BTC)(2)(m-bix)(3)](n)center dot 4nH(2)O (1), ([Cd(HBTC)(H2O)]center dot(p-bix)(1/2)(H2O)(2))(n) (2) and [Zn-3(BTC)(2)(p-bix)(3)(H2O)(2)](n)center dot 4nH(2)O (3) (H3BTC = 1,3,5-benzenetricarboxylic acid, bix = bis(imidazol-1-ylmethyl)-benzene), have been synthesized under hydrothermal conditions and structurally characterized. In 1, three Cd(II) ions are all in a highly distorted octahedral coordination environment, and m-bix plays a bidentate bridging ligand. In 2, Cd(II) ion is also in a highly distorted octahedral geometry, but p-bix is not coordinated with Cd(II) ions. p-Bix acts as a guest molecule filling in the Cd-HBTC rectangular channel. The structure of 3 contains two kinds of unique Zn(II) ions, one is in tetrahedral geometry and the other is in ideal octahedral environment. All the three compounds are three-dimensional metal-organic frameworks. Their TG, IR and fluorescent spectra are also reported. Additionally, a new parameter sigma is proposed to quantify the distortion of an octahedral environment. (C) 2008 Elsevier B.V. All rights reserved.