Synthesis, structure and ESR spectrum of the triclinic and monoclinic forms of hydrated K-8[Mo-8(V-IV)V4O40]

The triclinic K-8[Mo-8(V-IV)V4O40]. 10H(2)O (I) and monoclinic K-8[Mo-8(V-IV) V4O40]. 9H(2)O (II) have been prepared from molybdenum(VI)-oxide and ammonium vanadate in aqueous solution by adding potassium hydroxide and their structures characterized by ESR spectra and X-ray structure analysis. The structure of the same [Mo-8(V-IV)V4O40](8-) anion in both compounds is based on a central VO4 tetrahedron surrounded by a puckered ring of eight edge-sharing MoO6 octahedra, with four VO4 tetrahedra filling the gaps between the pairs of octahedra. The ESR spectra of both compounds clearly indicate that one vanadium atom is in the +4 oxidation state. In the crystal structure molybdovanadate anions are interconnected by K+ ions and water molecules.