Synthesis and crystal structure of a new hydrated iron(III) vanadate Fe2(H2O)[V2O7.VO3(OH)]

A new hydrated iron(III) vanadate was synthesized by an aqueous route from a V2O5 suspension in boiling water and iron(III) nitrate. The crystal structure of this well-crystallized yellow solid was solved ab initio from conventional X-ray powder diffraction data. The unit cell is orthorhombic with a = 11.990(3), b = 9.496(2), c = 8.339(1) A, Z = 4, space group P212121. The refinement of 70 parameters by the Rietveld method, based on 1413 reflections, converged to the R-factors RF = 0.044 and Rwp = 0.097. The structure of Fe2(H2O)[V2O7·VO3(OH)] consists of a three-dimensional framework built from corner-sharing bi-tetrahedral V2O7 and independent tetrahedral VO3(OH) units interconnected with edge-sharing bi-octahedral Fe2O9(H2O) groups. A thermal study of this compound confirmed its water content and showed the existence of the corresponding anhydrous vanadate Fe2V3O10.5, which provides, upon heating, a mixture of the two known iron(III) vanadates, namely the triclinic FeVO4 and the Fe2V4O13 phases.