Synthesis and Characterization of a Soluble Vanadium-Containing Keggin Polyoxoniobate by ESI-MS and super(51)V NMR: (TMA) sub(9)[V sub(3)Nb sub(12)O sub(42)].18H sub(2)O

The vanadium-containing heteropolyoxoniobate (TMA) sub(9)[V sub(3)Nb sub(12)O sub(42)].18H sub(2)O was synthesised by hydrothermal reaction of V sub(2)O sub(5) and hydrous niobium oxide in tetramethylammonium hydroxide solution. The cluster has an alpha -Keggin structure with a central VO sub(4) and two trans-bicapped VO sub(5). The water-soluble product was characterised by X-ray crystallography, ESI-MS and both liquid- and solid-state super(51)V NMR spectroscopy. The solid- and solution-phase super(51)V NMR spectra indicate two major peaks corresponding to one VO sub(4) and two VO sub(5) sites. A tetramethylammonium salt of vanadium-bearing polyoxoniobate ion (TMA) sub(9)[V sub(3)Nb sub(12)O sub(42)] in the alpha -Keggin structure is described. The compound is very soluble in water and stable near neutral pH.