Abstract

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) Å, Z = 4, space group P2₁2₁2₁. The refinement of 70 parameters by the Rietveld method, based on 1413 reflections, converged to the R-factors R_F = 0.044 and R_wp = 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 Fe₂V₃O_10.5, which provides, upon heating, a mixture of the two known iron(III) vanadates, namely the triclinic FeVO₄ and the Fe₂V₄O₁₃ phases.