Structure and cation distribution of new ternary vanadates FeMg₂V₃O₁₁ and FeZn₂V₃O₁₁

FeMg₂V₃O₁₁ crystals grown from a MgO/Fe₂O₃/V₂O₅ melt crystallize in the triclinic space group P-1 with parameters: a = 6.434(1) angstroms, b = 6.806(1) angstroms, c = 10.085(1) angstroms, α = 97.44(1)°, β = 103.44(1)°, γ = 101.56(1)° and Z = 2. FeZn₂V₃O₁₁ crystals grown from a ZnO/Fe₂O₃/V₂O₅ melt also crystallize in P-1 with similar parameters: a = 6.455(1) angstroms, b = 6.834(1) angstroms, c = 9.988(1) angstroms, α = 97.65(1)°, β = 102.61(1)°, γ = 101.26(1)° and Z = 2. Both are isostructural with GaZn₂V₃O₁₁, and susceptibility measurements reveal that all iron is high spin d⁵. In FeMg₂V₃O₁₁, Fe³ is distributed non-statistically with Mg²⁺ on octahedral and bipyramidal sites. In FeZn₂V₃O₁₁, Fe³⁺ is found only on the octahedral sites and Zn²⁺ exclusively occupies the bipyramidal sites.