Crystal Structure and Spectroscopic Characterization of K8(VO)2O(SO4)6

Red and yellow dichroistic crystals of a vanadium(V) compound, potassium ((mu)-oxo, di-(mu)-sulfato)bis(oxodisulfatovanadate), K8 (VO)2O(SO4)6, have been obtained from the ternary catalytic model melt system K2S2O7-K2SO4-V2O5. By slow cooling of the melt from 420 to 355 °C, crystal growth occurred, using solid V2O5 crystals present in the melt as nucleation promoter. The compound crystallizes in the monoclinic space group P2l with a = 13.60(9) (angstrom), b = 13.93(9) (angstrom), c = 14.05(9) (angstrom), (beta)= 90.286(10)°, and Z = 2. It contains two VO6 octahedra linked together by a (mu)-oxo and two (mu)-sulfato bridges. Furthermore, each octahedron has two monodentate sulfate ligands, making the dimeric entity coordinatively saturated. IR spectroscopy shows bands arising from V-O-V and V=O stretches as well as splitting of sulfate bands due to the different degrees of freedom present for different conformations of sulfate ligands. The coordination of vanadium in K8(VO)2O(SO4)6 is discussed in relation to the reaction mechanism of SO2 oxidation catalysis.