Crystal Structure and Spectroscopic Properties of CsVO₂SO₄

Dark crystals of the V(V) compound CsVO2SO4, suitable for X-ray investigations have been obtained from the catalytically important Cs2S2O7−V2O5 system. By cooling of the mixture with the composition XV2O5 = 0.5, some crystals were obtained in the otherwise glassy sample. The compound crystallizes in the orthorhombic space group Pbca with a = 6.6688(13) Å, b = 10.048(2) Å, and c = 17.680(4) Å at 20 °C and Z = 8. It contains a coordination sphere with a short V−O bond of 1.595(2) Å and trans to this the closest VO distance at 3.4 Å and four equatorial V−O bonds in the range 1.725(1)−1.984(2) Å. The deformation of the VO6 octahedron is thus much more pronounced compared to other known oxo sulfato V(V) compounds, and the coordination polyhedron of V(V) should be regarded as a tetragonal pyramid with the vanadium atom in the center. Each VO2+ group is coordinated to the neighboring groups by oxygen and sulfate double bridges in a zigzag structure where two sulfate oxygens virtually remain uncoordinatedone is found at the very long nonbonding V−O distance from the neighboring chain. This is the first time that we find pentacoordination of vanadium in the 12 different V(III), V(IV), and V(V) compounds examined so far. The FTIR and Raman spectra of the compound are in agreement with the simple formula unit of the investigated compound.