Synthesis, Characterization, and Thermostability of Four Novel Cadmium(II) Coordination Polymers with Mixed Ligands

Four novel mixed-ligand complexes were obtained from the reaction of maleic acid, diimine chelating ligands and Cd(OH)2 or CdO in a mixed solvent of water and methanol. The complexes were characterized by IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The results show that all the four complexes are coordination polymers. [Cd(phen)(H2O)(male)]n.2nH2O (1) and [Cd(bipy)(H2O)(male)]n.2nH2O (2) (male = maleate; phen = 1, 10-phenanthroline, bipy = 2, 2'-bipyridine) are isomorphic, and the asymmetric unit is constructed by one CdII atom, a maleate group, a diimine ligand and two crystal water molecules. Each maleate group links two CdII atoms in a bis(bidentate) chelating mode, resulting in a 1D helical chain. Within [Cd(phen)(H2O)2(male)]n.2nH2O (3), the maleate group bridges two CdII atoms in a bis(monodentate) chelating mode into a 1D helical chain along the [100] direction. The helical chain is decorated by phen groups alternatively at the two sides, and each phen plane of one chain is inserted in the void space between two adjacent phen ligands from an adjacent chain, resulting in a double zipper-like chain. The asymmetric unit of [Cd2(phen)2(male)2]n (4) contains a CdII cation, one phen molecule, and a maleate group, and one bridging maleate group links three CdII atoms resulting in a 2D layer extending in [011] plane. The 2D networks are constructed by four kinds of rings formed by the central metal atom and maleate dianion. The thermostabilities of the four complexes were investigated.