Structural Comparison of Iron Tetrapolyvanadate Fe<sub>2</sub>V<sub>4</sub>O<sub>13</sub> and Iron Polyvanadomolybdate Fe<sub>2</sub>V<sub>3.16</sub>Mo<sub>0.84</sub>O<sub>13.42</sub>: A New Substitution Mechanism of Molybdenum(VI) for Vanadium(V)
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Single crystals of the iron tetrapolyvanadate Fe2V4O13 and the iron polyvanadomolybdate Fe2V3.16Mo0.84O13.42 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 V4O136- clusters in Fe2V4O13 were ordered while the U-shaped [V3.16Mo0.84O13.42]6- clusters in Fe2V3.16Mo0.84O13.42 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 Fe2V3.16Mo0.84O13.42, 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.
