Regioselective synthesis and characterization of monovanadium‐substituted β‐octamolybdate [VMo7O26]5−

The monovanadium‐substituted polyoxometalate anion VMo₇O₂₆]^5?, exhibiting a β‐octamolybdate archetype structure, was selectively prepared as pentapotassium hexaikosaoxido(heptamolybdenumvanadium)]ate hexahydrate, K₅VMo₇O₂₆]·6H₂O ( VMo₇ ), 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 VMo₇ was also confirmed by elemental analyses and IR spectroscopy. The selectivity of the synthesis was inspected by a ⁵¹V NMR investigation which showed that this species bound about 95% of V^V in the crystallization solution. Upon dissolution of VMo₇ in aqueous solution, the VMo₇O₂₆]^5? anion is substantially decomposed, mostly into VMo₅O₁₉]^3?, α‐VMo₇O₂₆]^4? and V₂Mo₄O₁₉]^4?, depending on the pH.