V<sup>III</sup>V<sup>IV</sup><sub>3</sub>O<sub>3</sub>(PO<sub>4</sub>)<sub>3</sub>:  A Novel Vanadium Phosphate for Selective Oxidation of Light Hydrocarbons

A novel vanadium(IV) phosphate V<sup>III</sup>V<sup>IV</sup><sub>3</sub>O<sub>3</sub>(PO<sub>4</sub>)<sub>3</sub> has been synthesized and crystallized (1073 K, sealed silica tube, a few milligrams of PtCl<sub>2</sub> as mineralizer). According to the single-crystal structure analysis [orthorhombic, <i>F</i>2<i>dd</i> (No. 63), <i>Z</i> = 24, <i>a</i> = 7.2596(8) Å, <i>b</i> = 21.786(2) Å, <i>c</i> = 38.904(4) Å (lattice parameters from Guinier photographs), R<sub>1</sub> = 0.032, wR<sub>2</sub> = 0.067, κ-CCD diffractometer, 83 949 reflections measured, 6836 independent, 5986 with <i>I</i> > 2σ(<i>I</i>), 299 variables], V<sup>III</sup>V<sup>IV</sup><sub>3</sub>O<sub>3</sub>(PO<sub>4</sub>)<sub>3</sub> belongs to the Lipscombite/Lazulite structure family. At 1073 K V<sup>III</sup>V<sup>IV</sup><sub>3</sub>O<sub>3</sub>(PO<sub>4</sub>)<sub>3</sub> is in thermodynamic equilibrium with (VO)<sub>2</sub>P<sub>2</sub>O<sub>7</sub>, VO<sub>2</sub>, and VPO<sub>4</sub>. Substitution of V<sup>3+</sup> in V<sup>III</sup>V<sup>IV</sup><sub>3</sub>O<sub>3</sub>(PO<sub>4</sub>)<sub>3</sub> by Cr<sup>3+</sup> and Fe<sup>3+</sup> is possible. Like vanadylpyrophosphate the oxide phosphates M<sup>III</sup>V<sup>IV</sup><sub>3</sub>O<sub>3</sub>(PO<sub>4</sub>)<sub>3</sub> (M<sup>III</sup>:  V, Cr, Fe) show significant catalytic activity in selective oxidation of <i>n</i>-butane and 1-butene to maleic acid anhydride.