Synthesis, Structure And Properties Of Hybrid Compound Based On POMs And Pyridine Carboxylic Acid

Polyoxometalates（POMs）constitute a fascinating class of metal–oxygen clustercompounds with definite size and shape.Polyoxometalates has the redox properties,large size and diverse topologies.Therefore,the design and synthesis of POM-based hybrid inorganic–organic compounds has still been an important research field in inorganic chemistry.By adjusting center heteroatom,the composition and oxidation state of atom in the POMs,assembled into supramolecular structure,one–dimensional,two–dimensional,three–dimensional with organic ligand or metal-organic groups.Therefore,the inorganic–organic hybrid compounds have been greatly enriched.These inorganic–organic hybrid compounds have still been a research field of rapid expansion due to their variety of crystal structure and their tremendous potential applications in fields like photocatalysis,magnetism,adsorption,macromolecule crystallography and biocatalysis.In this paper,three different organic-inorganic hybrid compounds have been synthesized with 2,6-pyridinedicarboxylic acid as ligand and three different heteropoly acids under hydrothermal conditions and characterized.For studying the structure and property of these hybrid compounds,much work have been done.The main contents of this paper include the following three parts:1.A new kind of inorganic–organic hybrid compound[(PMo₁₂O₄₀)（C₅H₆N）₃]（CCDC:1403416）has been synthesized with phosphomolybdic acid and 2,6-pyridinedicarboxylic acid under hydrothermal conditions and characterized by single crystal X-ray diffraction,XRD,IR,UV,TG-DTA,XPS and elemental analysis.The crystal belongs to the monoclinic system,space group P2（1）/n,a=12.2013（9）?,b=13.9820（10）?,c=12.9649（10）?,α=90.00°,β=98.6650（10）°,γ=90.00°,V=2186.5（3）?³,Z=2.The single crystal X diffraction results show that the single crystal is a two-dimensional structure.Further study showed that,the compound shows multifunctionalities such as fluorescence,electrochemical property and selective adsorption of the cationic organic dye methylene blue molecules.2.A new kind of inorganic–organic hybrid compound(SiMo₁₂O₄₂)（C₅H₆N）₄·H₂O（CCDC:1422988）has been synthesized with ammonium molybdate,sodium silicate and 2,6-pyridinedicarboxylic acid under hydrothermal conditions and characterized by single crystal X-ray diffraction,XRD,IR,fluorescence,UV,TG-DTA,XPS and elemental analysis.The crystal belongs to the Orthorhombic system,space group Pnma,a=16.6601（13）?,b=20.937（2）?,c=14.0142（13）?,α=90.00°,β=90.00°,γ=90.00°,V=4888.3（8）?³,Z=4.The single crystal X diffraction results show that the single crystal is a two-dimensional structure.Further study showed that,the UV spectrum shows the hybrid compound has a peak at 263 nm and attributed to theπ→π*transition of the pyridine ring[C₅H₆N].The electrochemical results show that the hybrid compound has three pairs of reversible in the range of-0.4⁰.5V.The TG-DTA curve shows that the hybrid compound is lost in one step and the remainder is the oxide of Si and Mo.The XPS test shows that Si is+2 valence and Mo is+6valence in the hybrid compound.3.A new kind of inorganic–organic hybrid compound[H_0.5P₂W₁₈O₆₂][C₅H₆N]₃（CCDC:1422987）has been synthesized with phosphoric acid,sodium tungstate and2,6-pyridinedicarboxylic acid under hydrothermal conditions and characterized by single crystal X-ray diffraction,XRD,IR,fluorescence,UV,TG-DTA,XPS and elemental analysis.The crystal belongs to the Monoclinic system,space group C2/m,a=26.7659（18）?,b=13.9721（8）?,c=20.8032（15）?,α=90.00°,β=102.104（3）°,γ=90.00°,V=7606.9（9）?³,Z=4.The single crystal X diffraction results show that the single crystal is a two-dimensional structure.Further study showed that,the UV spectrum shows the hybrid compound has two peaks at 259nm and 264nm,duing to theπ→π*transition of the pyridine ring[C5H6N].The electrochemical results show that the hybridcompound has four pairs of redox peaks in the range of-0.1⁰.4V.The TG-DTA curve shows that the hybrid compound is lost in two steps and the remainder is the oxide of Si and Mo.The XPS shows that P is+5 valence and W is+6valence in the hybrid compound.