Synthesis, Characterizations Of Coordination Polymer Of Transition Metal With Pyrazine And Pyridine Dicarboxylic Acids

Pyrazine-2,3-dicarboxylic acid and pyridine-2,6-dicarboxylic acid containing N-and O-donors, can form coordination bonds with metal ions of different soft and hard degree. Meanwhile carboxyl groups have so much varieties of coordination modes, so it can build many novel coordination polymers with unique functions. Metal ions, co-ligand, pH value, and other factors may influence their coordination modes. Furthermore, hydrogen bonding, supermolecular contacts orπ-πstacking interactions make the framework more stable. So we studied the reaction of the above two ligands and transition metals in this paper, mainly researching synthesis method of coordination which have different structures. We had synthesized seven compounds and made some characterizations through crystal X-ray diffraction, X-ray powder diffraction, IR and thermogravimetric analysis. Within all the compounds, some were made fluorescent characterization.[Cu(pzdc)(phen)(H2O)-4H2O]n[1] was obtained by mixing CuCl2·2H2O, phen and pyrazine-2,3-dicarboxylic acid directly, which is a mononuclear compound. In compound [1], the Cu(II) atom is coordinated by one carboxyl oxygen atom,one water oxygen atom, one nitrogen atom from the pzdc2- ligand and two nitrogen atoms from a terminal phen, forming a square-pyramidal geometry; The extended 3D framework of complex [1] was gained by hydrogen bonds andπ-πinteraction.[Co(Hpzdc)2·2H2O]n[2] was obtained by mixing pyridine-2,6-dicarboxylic acid, pyrazine-2,3-dicarboxylic acid and CoCl2·6H2O directly, but no pyridine-2,6-dicar-boxylic acid compound was gained. In compound [2], there is a 1D complex chain along the c axis, and every Hpzdc1- ligand is coordinated to two cobalt atoms through two oxygen atoms from its two carboxylate groups and one nitrogen atom. The extended 3D framework of complex [2] is combined by hydrogen bonds andπ-πinteraction which exist between the adjacent chains. In most of the H2pzdc complexes, H2pzdc ligand is in the dianion form. It is quite rare to find that the acid ligand in the complex [2] is in monoanion form(Hpzdc1-).[Mn(pzdc)(phen)-H2O]n[3] was obtained by mixing the MnCl2·6H2O, phen and pyrazine-2,3-dicarboxylic acid directly. By bridging two pairs of pzdc2- ligands, the adjacent Mn(II) atoms form distinctive squares. Every pzdc2- ligand is coordinated to three manganese atoms through three oxygen atoms from its two carboxylate groups and one nitrogen atom, and pzdc2- ligand plays a connective function in the complexes. Through hydrogen bonds andπ-πstacking interactions the complex is further converted into a three-dimensional framework.Compound [4], [5] and [6] were respectively obtained by mixing the pyrazine-2,3-dicarboxylic acid with CoCl2-6H2O, CdCl2·5/21120 and ZnCl2·2H2O at normal temperature. Although co-ligand were added to the system, they did not participate in the coordination. In compound [4], every pzdc2- ligand is coordinated to two Co(II) atoms through two N atoms and two O atoms, forming 1D chain structure. There are some intermolecular hydrogen bonds between the uncoordinated water molecules and the carboxyl oxygen atoms in the network, which make the complex converting into a three-dimensional framework. Compound [4], [5] and [6] were reported compounds.[Mn2(pda)2(H2O)3]n [7] was obtained by mixing pyridine-2,6-dicarboxylic acid, pyrazine-2,3-dicarboxylic acid and MnCl2-6H2O at hydrothermal condition. In compound [7], Mn(II) ions are linked via alternative single and double oxygen brigeds to form a 1D Zigzag chain; There is intermolecularπ-πinteraction between the chains, which makes the compound become a 3-D framework. Intermolecular hydrogen bonds make the framework more stable. Each pda2- can be described as a tridentate building block which links three Mn centers. To the best of our knowledge, the coordination behavior of pda2- is unusual. There is only one similar example:{[Zn(PDA)(H2O)1.5]}n and polymeric complexes formed by Mn(Ⅱ) and 2,6-pda are rare. Three compounds are new polymers among the seven synthesized compounds.