Structural Comparison of Iron Tetrapolyvanadate Fe₂V₄0₁₃ and Iron Polyvanadomolybdate Fe₂V_3.16Mo_0.84O_13.42: A New Substitution Mechanism of MoIybdenum(VI) for Vanadium(V)

Single crystals of the iron tetrapolyvanadate Fe₂V₄O₁₃ and the iron polyvanadomolybdate Fe₂V_3.16Mo_0.84O_13.42 were grown from Fe₂O₃/V₂O₅ and Fe₂O₃/V₂O₅/MoO₃ melts, respectively, Single-crystal X-ray diffraction revealed that the two structures are closely related. Both contained isolated Fe₂O₁₀ octahedral dimers with similar orientations. The unusual U-shaped V₄O₁₃^6-clusters in Fe₂V₄O₁₃ were ordered while the U-shaped [V_3.16Mo_0.84O_13.42]^6- clusters in Fe₂V_3.16Mo_0.84O_13.42 were disordered. The substitution of molybdenum(VI) for vanadium(V) revealed a new substitution mechanism, in which a corresponding stoichiometric amount of oxygen was brought into the structure for charge balance with no reduction of the V⁵⁺ and Mo⁶⁺ ions. Crystal data: for Fe₂V₄O₁₃, monoclinic, space group P2₁/c (No. 14), with a = 8.300(2) Å, b =9.404(6) Å, c = 14.560(2) Å, β = 102.08(1)°, and Z = 4; for Fe₂V_3.16Mo_0.84O_13.42, monoclinic, space group P2₁/c (No. 14), with a = 7.678(1) Å, b = 9.456(2) Å, c = 8.336(2) Å β = 109.50(2)°, and Z = 2.