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, [Cd3(BTC)2(m-bix)3]n·4nH2O (1), {[Cd(HBTC)(H2O)]·(p-bix)1/2(H2O)2}n (2) and [Zn3(BTC)2(p-bix)3(H2O)2]n·4nH2O (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 σ is proposed to quantify the distortion of an octahedral environment.