Crystal Structure and Raman Spectroscopy of FeVMoO7 and CrVMoO7 with MoO Double Bonds

Single crystals of FeVMoO7 and CrVMoO7 were grown by a flux method from Fe2O3−V2O5−MoO3 and Cr2O3−V2O5−MoO3 melts, respectively. Single-crystal X-ray diffraction revealed that FeVMoO7 and CrVMoO7 are isostructural, in which V5+ and Mo6+ ions in the [VMoO7]3- units are crystallographically distinct, and one type of oxygen is bonded only to molybdenum, forming a MoO double bond. These rare structural features were also studied by infrared and Raman spectroscopy. Raman MoO stretching frequencies are consistent with the assignments made in previous surface studies of molybdate catalysts. Crystal data for FeVMoO7: triclinic, space group P1̄ (No. 2), with a = 5.564(1) Å, b = 6.669(1) Å, c = 7.909(1) Å, α = 97.65(1)°, β = 90.33(1)°, γ = 101.32(2)° and Z = 2. Crystal data for CrVMoO7: triclinic, space group P1̄ (No. 2), with a = 5.5273(9) Å, b = 6.582(1) Å, c = 7.8650(9) Å, α = 96.19(1)°, β = 89.87(1)°, γ = 102.01(1)°, and Z = 2.