Synthesis, Characterization and The Effect of the Auxiliary Ligands on the Dimensionality of Two Cobalt(II)-Fumarate Coordination Polymers with Bis(imidazole) Ligands

Abstract

Two new Co(II) coordination polymers, namely {[Co(m-fum)0.5(m-obix)2(H2O)](NO3)}n (1), {[Co(m-fum)0.5(m-mbix)2(H2O)](NO3)}n (2), (H2fum: fumaric acid, obix:1,2-bis(imidazol-1-yl-methyl)benzene, mbix: 1,3-bis(imidazol-1-yl-methyl)benzene), have been successfully synthesized under hydrothermal conditions. They have been structurally characterized by elemental analysis, IR spectra, single crystal X-ray diffraction, powder X-ray diffraction (PXRD), magnetic properties. Single-crystal X-ray analysis reveals that the asymmetric units of both CPs contain a Co(II) ion, half fumarate ligand, two bis(imidazole) ligands, one aqua ligand and a nitrate ion. While two symmetry-related Co1 ions are connected by one fumarate ligand to generate a dinuclear unit and obix ligand links adjacent dinuclear units through the nitrogen atoms to form a 1D double chains in 1, each mbix ligand links two Co1 ions to form 1D double chains, and the adjacent chains are further linked together by fumarate ligands to form a 2D network in 2. The effect of bis(imidazole) ligands, which are o- and m-isomers, on the dimensionality of the formed coordination polymer was investigated. The reason for this great effect of bis(imidazole) ligands is that adjustments in the framework occur result of the bending of the semi-rigid imidazole ligands. Thermal analysis shows that 1 and 2 possess similar thermal behaviors. The optical band gap energy values of 1 and 2 observed 3.24 eV and 3.21 eV, respectively. This small difference in the band gap energy may be due to the difference in structural arrangement.