Synthesis,Crystal Structures And Properties Of Polymetallic Tungsten-titanium Oxide Cluster Complexes

Polyoxometalate is a kind of excellent inorganic material.It not only has a variety of electronic structures and sizes,but also has its unique functional properties,such as acid-base,multi-electron,redox,thermal stability and so on.It has potential application prospects in many research fields,especially in catalysis,materials and drugs.In addition,as a molecular model compound of nano-TiO2 material structure and catalytic performance,crystal titanium oxide clusters with clear structure have gradually become the focus of researchers.In this paper,a new type of tungsten-titanium-oxygen cluster complex was designed and synthesized by using classical Keggin-Heteropolytungstate and water-soluble titanium as precursors,and the synthesis conditions and related properties were studied.In this paper,two layered titanium-oxygen cluster complex based on pyridine dicarboxylic acid ligand,two keggin-type polymetallic tungsten-titanium oxide cluster complexes and a case of rare earth metal complexes has been synthesized by conventional aqueous solution method.The crystal structure was characterized and the semiconductor properties,fluorescence properties,photocatalytic properties and electrocatalytic properties of the compounds were studied.1.In the conventional aqueous solution system,TiCl₄ and 2,6-pyridine carboxylic acid ligands were used to synthesize layered titanium oxide cluster complex by low temperature reaction with the aid of H₂O₂ under alkaline conditions:K₉[Ti₃O₄?O₂?₃?C₇H₃O₄N?₃?OH₂?₂]Cl·4H₂O?1?In the crystal structure of 1,the polyanions[Ti₃O₄?O₂?₃?C₇H₃O₄N?₃?OH₂?₂]^8-coordinate with potassium cations via O atoms of the?O₂?^2-group and O atoms of carboxy groups to form the subunit structure of 1.The sub-units are then extended through potassium ions to form a grid structure.The results of solid UV diffuse reflectance spectra and Mott-Schottky curves show that the compound belongs to n-type semiconductor.Photocatalytic degradation of dye pollutants and photocatalysis of dopamine showed that 1 could be used as a good photocatalyst and photochemical sensor material.2.Using Na₉[?-SiW₉O₃₄H]and K₇H[Ti₆O₉?ida?₆]as precursors in conventional aqueous solutions,two keggin-type Polymetallic Tungsten-Titanium oxide Cluster complexes were obtained:(C₄H₁₂N)₁₄Si₂W₁₈Ti₆O₇₇·27H₂O?2??C₂H₈N?₁₂H₂Si₂W₁₈Ti₆O₇₇·17H₂O?3?Compounds 2 and 3 are heterogeneous isomorphism,and their anions are dimer structures composed of two Keggin-type"SiW9Ti3O40"units connected by three Ti-O-Ti.The"SiW₉Ti₃O₄₀"is formed by three TiO₆ octahedrons that make up for the three corner-shared WO₆ octahedrons missing in Keggin's"A-?-SiW₉O₃₄^10-".The results of solid UV diffuse reflectance spectra and Mott-Schottky curves show that the compounds belongs to n-type semiconductor.The results of photoconductive properties of 2 and 3 show that the two compounds have good semiconductor properties.3.1 was used as the precursor in conventional aqueous solution.Two new compounds were obtained by changing the solution pH,to degrade and reassemble the structure of 1:K₂H₂[Ti₂O?O₂?₂?C₇H₃O₄N?₂?OH₂?₂]₂·9H₂O?4?Na_1.7K_1.3[Ce?C₇H₃O₄N?₃]·9H₂O?5?Compound 4 is a unique grid-like structure formed by the coordination of[Ti₂O?O₂?₂?C₇H₃O₄N?₂?OH₂?₂]^2-anions with Na⁺and K⁺.Compound 5 is a flower-like structure of pyridine dicarboxylic acid formed by the coordination of N and carboxyl O with Ce³⁺.Through the measurement and calculation of solid UV diffuse reflectance spectrum,the band gap is 2.08 eV.The electrocatalytic properties of 4 and 5 were studied.The results show that both 4 and 5 have good catalytic effect on NO₂^-.