Synthesis, Structure And Properties Of The Coordination Polymers Constructed By Pyrazinetetracarboxylic Acid And Lanthanides

Coordination polymers are polymeric, supramolecular assemblies of metalions (or metal clusters) and organic ligands linked through coordination bonds. Because of their novel structures and unique physicochemical properties, coordination polymers have potential applications in molecule identification, catalysis, adsorption, etal. Pyrazine tetracarboxylic acid(PTCA) is a polydentate organic ligand containing N,O atoms, which can coordinate to several metal ions and may exhibit various coordination modes. Thus it is a good candidate for synthesizing novel complexes. Because rare earth elements have many empty orbits, they can react coordinately with organic ligands to get complexes with unique fluorescent and magnetic properties.In this paper, we used PTCA and rare earth nitrates (dysprosium nitrate, europium nitrate, terbium nitrate, gadolinium nitrate) synthesized a series of coordination polymers through hydrothermal method and solvent evaporation method, and characterized them by single-crystal X-ray diffraction, X-ray diffraction, elemental analysis, infrared spectroscopy, thermogravimetric analysis and fluorescence analysis. The main work is listed as follows:1. PTCA was synthesized starting from phenazine.2. Three rare earth complexes(1)- (3)have been synthesized by the solvothermal reactions of PTCA with dysprosium nitrate, terbium nitrate and europium nitrate respectively. Complexes (1) is a three-dimensional coordination polymer. It crystallizes in the triclinic system, space group P-l,with a=9.0069(4) (?), b=10.8801 (2) (?), c=13.246 (?),α=68.725 (8)°,β=77.990 (8)°,γ=88.618(10)°. The Dy(Ⅲ) ions in complexes(1) are nine-coordinated and eight-coordinated. The nine-coordinated Dy(Ⅲ) ion coordinated with PTCA directly while the eight-coordinated ones formed a metal-oxygen atoms cluster with carboxyl, hydroxyl and water. The two parts of the structure are connected by carboxyl's bridge tridentate coordination mode. Complexes (2) and (3) have the similar structure tested by IR, XRD etal.3. Complexes (4)-(6) have been synthesized with the same ligand and europium nitrate, terbium nitrate and gadolinium nitrate respectively at room temperature. Some related tests result show that structure of complex (4) is similar to that of complex (6) while complex (5) has a different structure than them. Furthermore, all the three complexes have better thermal stability, but the fluorescence properties of the large difference.