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 novel heterobimetallic 2D coordination polymers were synthesized.•Two coordination compounds are studied both in the solid state and solution.•Cyclic voltammograms were carried out with carbon paste electrode.

Two new 2D heteronuclear coordination polymers with Ni(II), Zn(II) and Ca(II), namely {(dapH)2[CaM2(pydc)4(H2O)2]·2H2O}n (M = Ni (1) and M = Zn (2)) where [pydcH2 = 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 P21/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.

Graphical abstractTwo new 2D heteronuclear coordination polymers with Ni(II), Zn(II) and Ca(II), with dipicolinic acid and 3,4-diaminopyridine were synthesized and characterized. In these new supramolecular coordination polymers, existent species join together with the cooperation of multiple inter/intra-molecular classical O–H⋯O, N–H⋯O and non-classical C–H⋯O hydrogen bonds (H-bonds), offset face to face π–π, edge to face C–H⋯π and C–O⋯π stacking interactions in the form of various homo/hetero-synthons leading to three-dimensional supramolecular networks.Figure optionsDownload full-size imageDownload as PowerPoint slide