Configurational Isomerism in Polyoxovanadates.

A water-soluble derivative of the polyoxovanadate {V E O } (E=semimetal) archetype enables the study of cluster shell rearrangements driven by supramolecular interactions. A reaction unique to E=Sb, induced exclusively by ligand metathesis in peripheral [Ni(ethylenediamine) ] counterions, results in the formation of the metastable α * configurational isomer of the {V Sb O } cluster type. Contrary to all other polyoxovanadate shell architectures, this isomer comprises an inward-oriented vanadyl group and is ca. 50 and 12 kJ mol higher in energy than the previously isolated α and β isomers, respectively. We discuss this unexpected reaction in light of supramolecular Sb-O⋅⋅⋅V and Sb-O⋅⋅⋅Sb contacts manifested in {V Sb O } dimers detected in the solid state. ESI MS experiments confirm the stability of these dimers also in solution and in the gas phase. DFT calculations indicate that other, as of yet elusive isomers of {V Sb }, might be accessible as well.