Three new supramolecular compounds of copper (II), cobalt (II) and zirconium (IV) with pyridine-2,6-dicarboxylate and 3,4-diaminopyridine: Solid and solution states studies

Three new Cu(II), Co(II) and Zr(IV) compounds, [Cu(pydcH)(pydcH2)]·OH−·2H2O (1), (dapH2)[Co(pydc)2]·pydcH2·4H2O (2) and (dapH)2[Zr(pydc)3]·0.5H2O (3) [pydcH2 = pyridine-2,6-dicarboxylic acid, dap = 3,4-diaminopyridine] have been synthesized and characterized by elemental analysis, spectral (IR, UV–Vis), thermal (TG/DTG/DTA) analysis, electrochemical and X-ray single crystal diffraction. Compound 1 consists of a cationic complex and in 1 the acid is coordinated to metal ion in the neutral form, which is quite rare, whereas 2 and 3 are anionic complexes with dianionic ligands. In all the compounds, the acid is coordinated to the metal center in a tridentate fashion. The coordination polyhedron in 1 and 2 is a distorted octahedron, however for 3 it is a distorted tricapped trigonal prism. These compounds are stabilized in the solid state by a complicated network of hydrogen bonds between crystallization water molecules, anionic and cationic fragments, which form 3D-supramolecular arrays. Furthermore hydrogen bonds, π–π and C–O⋯π stacking interactions seem to be effective in stabilizing the crystal structures. The complexes and dap ligand were additionally tested for their antibacterial properties. The protonation constants of pydc and dap, the equilibrium constants for the pydc-dap proton transfer system, the stoichiometry and stability of complexation of this system with Co2+, Cu2+ and Zr4+ ions in aqueous solution were investigated by the potentiometric pH titration method. The stoichiometries of most of the complex species in solution were found to be very similar to the cited crystalline metal ion complexes.

Three new coordination compounds of Cu(II), Co(II) and Zr(IV) with dipicolinic acid and 3,4-diaminopyridine were synthesized and characterized by the methods of elemental, spectroscopic (IR and UV–Vis), thermal (TG/DTG, DTA) analysis, electrochemical and single crystal X-ray diffraction. They were also investigated by solution studies. The complexes and dap ligand were additionally tested for their antibacterial properties.Figure optionsDownload as PowerPoint slideHighlights
► Three supramolecular compounds of Cu(II), Co(II) and Zr(IV) have been prepared.
► The copper (II) and Co(II) centers are distorted octahedral but the Zr(IV) center is distorted tricapped trigonal prismatic.
► All the compounds were studied both in the solid state and solution.
► Cyclic voltammograms of 1 and 2 were carried out with a carbon paste electrode.
► Compound 1 has higher activity than the other compounds against microorganisms.