Syntheses, Structures And Properties Of Metal-Organic Coordination Polymers

Metal-Organic coordination polymers are formed by self-assemblythrough coordination bonds between bidentate or multbentate organic ligands and central metal ions. The central ion, in general, is transition metal ion with a definite coordination model, acting as template and organic ligand with many coordination sites, acting as building block. In coordination polymers, bidentate or multibentate ligands coordinate with one metal ion or two different metal ions to construct 0-D, 1-D, 2-D or 3-D covalent frameworks between which hydrogen bonds may be formed to build up hydrogen-bonding networks. Diversified structures of the coordination polymers result in unusual properties of the novel materials.In this paper, according to principles of molecular design, Cu(Ⅰ), Cu(Ⅱ),Ag(Ⅰ), Pd(Ⅱ) were selected as templates, and 2,2'-Bipyridyl-3,3'-dicarboxylic acid (H2bpdc) mainly acted as building blocks. A novel coordination polymer was synthesized under solvothermal conditions and the crystal structure was determined, of which electrical and thermal properties were also investigated.Solvothermal reaction is a method of synthesizing coordination polymers. It is more facile than homogeneous phase method. In this paper, we discussed the synthesis conditions in M-bpdc system, different center ions, mole ratio of reactants, solvents and pH values. The major contributions in the paper as follows:1. A novel [AgⅠ4 (bpdc)(H2bpdc)(Hbpdc)2]n was synthesized by the reaction of AgNO3 and H2bpdc under hydrothermal conditions.2. Characterizations of the crystal structuresSingle crystal structures of the new coordination polymer was determined by X-ray diffraction.[AgⅠ4 (bpdc)(H2bpdc)(Hbpdc)2]n has a 2-D layered structure, belonging to monoclinic crystal system, space group C2/c with cell parameters a = 1.9516(4) nm, b = 1.9503(4) nm, c = 1.2566(3) nm,β= 112.48(3)°,V = 4.4194(17) nm3, Z = 8. 3. Physical Properties (1) Crystal energy gap Crystal energy gap (Eg) was determined by UV-VIS-NIR reflectance spectrum. The energy gap of [AgⅠ4 (bpdc)(H2bpdc)(Hbpdc)2]n is 2.75 eV, which is a semiconductor. (2) Thermal stabilities[AgⅠ4 (bpdc)(H2bpdc)(Hbpdc)2]n is thermally stable up to 210℃, shown as its TG-DTA curve. The coordination polymer begins to decompose at this temperature.4. The investigation of synthesis conditions in solvothermal reactionsFor M-bpdc system , when bpdc ligand coordinated with IB metal ions Cu(Ⅱ) and Ag(I), it tended to form the stablest coordination model to obviously decrease the effects of solvothermal reaction conditions.