Hydrothermal Syntheses and Characterization of Two Multi-vanadium Capped Keggin Polyoxoniobates Derivatives

Abstract

Two organic-inorganic hybrid compounds constructed from polyoxoniobates and transition metal coordination complexes,[Cu(TETA) ] 4 [VNb 12(VO) 4 O 40 ][OH]·10H 2 O(1) and [Cu(TETA) ] 4 · [VNb 12(VO) 6 O 40 ][OH] 5 ·5H 2 O(2)(TETA = triethylenetetramine),have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analyses,IR spectra,X-ray photoelectron spectrum(XPS),powder X-ray diffraction(PXRD),thermogravimetric analysis(TGA) and elemental analyses.Compound 1 is a 3D tetra-capped vanadoniobates and compound 2 is a 3D hexa-capped vanadoniobates which are constructed from heteropolyoxometalates and [Cu(TETA) ]2 +fragments.The result of bond valence sum calculations indicates that the vanadium centers of VO 4 tetrahedral in{ VNb 12 } Keggin unit in compounds 1 and 2 are in oxidation state + Ⅴ whereas the remaining vanadium centers are in oxidation state + Ⅳ.This is in line with the analysis of X-ray photoelectron spectrum.