Regioselective synthesis and characterization of monovanadium-substituted β-octa­molybdate [VMo(7)O(26)](5−)

The monovanadium-substituted polyoxometalate anion [VMo(7)O(26)](5−), exhibiting a β-octa­molybdate archetype structure, was selectively prepared as penta­potassium [hexa­ikosaoxido(hepta­molybdenumvanadium)]ate hexa­hy­drate, K(5)[VMo(7)O(26)]·6H(2)O (VMo(7)), by oxidation of a reduced vanadomol­yb­date solution with hydrogen peroxide in a fast one-pot approach. X-ray structure analysis revealed that the V atom occupies a single position in the cluster that differs from the other positions by the presence of one doubly-bonded O atom instead of two terminal oxide ligands in all other positions. The composition and structure of VMo(7) was also confirmed by elemental analyses and IR spectroscopy. The selectivity of the synthesis was inspected by a (51)V NMR investigation which showed that this species bound about 95% of V(V) in the crystallization solution. Upon dissolution of VMo(7) in aqueous solution, the [VMo(7)O(26)](5−) anion is substanti­ally decomposed, mostly into [VMo(5)O(19)](3−), α-[VMo(7)O(26)](4−) and [V(2)Mo(4)O(19)](4−), depending on the pH.