Synthesis, crystal structures, spectroscopic, thermal analysis, electrochemical and solution studies of two new mixed metal coordination polymers based on dipicolinic acid and 3,4-diaminopyridine

Two new 2D heteronuclear coordination polymers with Ni(II), Zn(II) and Ca(II), namely {(dapH) 2[CaM2 (pydc) 4(H2O)(2)] center dot 2H(2)O} n (M = Ni (1) and M = Zn (2)) where [pydcH(2) = pyridine-2,6-dicarboxylic acid (dipicolinic acid), dap = 3,4-diaminopyridine] have been synthesized and characterized by elemental analysis, infrared spectroscopy, thermal (TG/DTG/DTA) analysis, electrochemical as well as X-ray single crystal diffraction. The compounds 1 and 2 display isostructural features and crystallized in the monoclinic P2(1)/n space group. Both of the compounds contain cationic and anionic fragments and two uncoordinated water molecules. In 1 and 2 (pydc)(2) acts as tridentate ligands and connected to calcium ions through carboxylate bridging. Then each dipicolinate ligand bridges one calcium to a M(II) atom. The equilibrium constants of the binary, ternary and quaternary complexes of ligands or proton transfer system with metal ions in an aqueous solution were investigated by a potentiometric pH titration method. (C) 2013 Elsevier B.V. All rights reserved.