Syntheses, Structures And Properties Of Coordination Polymers With Azacyclic Dicarboxylates And/or Pseudohalides

Great efforts have been expended on the organic ligands containing carboxylate groups because of their fascinating structural diversity;this kind of ligands can offer great potentials for fine control over coordination architectures and applications in catalysis,luminescence,magnetism and porosity.Meanwhile,the study on the azido and thiocyanate ions has attracted more and more attention due to their significant contribution to magnetic coupling.Recently,a large number of compounds contain azido-carboxylate mixed bridges have been obtained.These two kinds of bridges have different influence on the magnetic properties.With this aims,dicarboxylates are used as bridging ligands between divalent transition metal ions,in combination with the use of azido or thiocyanate ions bridging ligands,twenty-four new coordination polymers,including one dimensional,two dimensional and three dimensional motifs, have been prepared,and the magnetic properties of some of the complexes have been characterized.1.Solvothermal reactions of dimethyl pyridazine-3,6-dicarboxylate and appropriate metal chlorides in the absence/presence of KCl,NaCl or NH₄Cl yielded a series of coordination compounds of pyridazine-3,6-dicarboxylate with Mn（Ⅱ）,Co（Ⅱ）,Ni（Ⅱ） and Zn（Ⅱ）.All the Mn（Ⅱ） compounds contain the anionic binuclear motif [Mn₂（pzdc）₃]^2- with the trigonal prismatic shape.Through the K/Na-O electrostatic coordination,charge-assisted N-H/O hydrogen bonds,and weak C-H/O hydrogen-bonds,the binuclear prismatic anion co-assembles with different cations ([Mn（H₂O）₆]²⁺,K⁺,Na⁺ or NH₄⁺) to generate 3D architectures.Under similar synthetic conditions,the Co（Ⅱ） and Ni（Ⅱ） ions always give the neutral binuclear molecules[M₂（pzdc）₂（H₂O）₄],which are self-assembled into 3D hydrogen-bonded networks.The Zn（Ⅱ） ion seems to be amphibious:in the presence of NH₄⁺,K⁺ and Na⁺,it forms the[Zn₂（pzdc）₃]^2- species that are isostructural with the Mn（Ⅱ） species, but the absence of the above cations leads to[Zn₂（pzdc）₂（H₂O）₄],which is isomorphous with the Co（Ⅱ） and Ni（Ⅱ） compounds.The different structures have been qualitatively explained based on the metal ionic size,ligand constraints, inter-ligand repulsion,ligand-field effects,and anionic-cationic interactions. Magnetic studies on selected Mn（Ⅱ） compounds reveal that weak antiferromagnetic coupling is operative through the triple pyridazine bridges within the prismatic anions. 2.A novel 2D coordination polymer consisting of ferromagnetic Ni（Ⅱ） chains with alternating double EO-azide bridges and（EO-azide）bis（carboxylate） triple bridges exhibits Solvent-modulated metamagnetism,and the reversible dehydration/hydration processes are accompanied by significant changes in critical temperature,critical field and hysteresis.Then another two compounds of Co（Ⅱ） and Mn（Ⅱ） that have the similar structure with the Ni（Ⅱ） compound were synthesized,and their reversible dehydration/hydration processes and the magnetic properties were analysed.By comparison,the（EO-azide）bis（carboxylate） triple bridges in Ni（Ⅱ） or Co（Ⅱ） chains mediate ferromagnetic interaction while this kind of bridge in Mn（Ⅱ） chain mediates antiferromagnetic interaction.3.Four new cadmium（Ⅱ） coordination polymers have been synthesized from appropriate Cd（Ⅱ） salts and 4-pyridylacrylic acid（4-Hpya） or 3-pyridylacrylic acid （3-Hpya） in the presence of thiocyanate under similar hydrothermal conditions.The use of cadmium perchlorate as metal source leads to complexes with 4-Hpya and 3-Hpya,while the use of cadmium acetate leads to complexes with 4-pya^- and 3-pya^-. Whether the ligand is protonated or not has much influence on the structure of these cmpounds,and the proton can plays an important role in assembling the chains into higher-dimensional networks via hydrogen-bonds.Besides,a Cu（Ⅱ） complex with azide and 4-Hpya has been synthesized and characterized crystallographically and spectroscopically,and the magneto-structural correlations have been discussed in comparison with other Cu（Ⅱ） dimers with the same bridging motif.