A new heterometallic supramolecular coordination polymer, namely [(1-mimH)[Nd(pydc)3Ca(pydcH2) (H2O)2]4H2O]n (where pydcH2 = pyridine-2,6-dicarboxylic acid (dipicolinic acid), 1-mim = 1-methylimidazole) has been prepared and characterized by elemental analysis, spectral (IR, UV–Vis), 1H NMR and 13C NMR spectroscopy, thermal analysis as well as single-crystal X-ray diffraction. The X-ray diffraction study demonstrates that the compound has a 1D network; the layers of this compound are connected by complicated hydrogen bonds to form 3D supramolecular architecture. The polymeric chain contains Nd(III) ions and Ca(II) ions bridged by (pydc)2- ligands. Each (pydc)2- ion is connected to one neodymium( III) ion as a tridentate ligand and one calcium ion via bridging carboxylate group. The equilibrium constants of dipicolinic acid and 1-methylimidazole, pydc/1-mim proton transfer system, as well as those of the complexes (binary, ternary, and quaternary) were investigated by potentiometric pH titration method.
