CRYSTAL-STRUCTURE AND SPECTROSCOPIC CHARACTERIZATION OF CSV(SO4)2 - EVIDENCE FOR AN ELECTRONIC RAMAN TRANSITION

Green platelike hexagonal crystals of CsV(SO4)2 were obtained by stepwise cooling in the range 500-400-degrees-C of solutions of V2O5 in Cs2S2O7, either under SO2(g) atmosphere or during catalytic conversion of SO2, in a 10% SO2, 11% O2, and 79% N2 gas mixture. The crystals belong to the trigonal system, space group P3BAR, with a = b = 4.868(1) A and c = 8.767(2) angstrom at 140 K and Z = 1. The phase represents a novel structure type with tetrahedral SO42- ions linked to octahedrally coordinated vanadium(III) in a way different from the known KV(SO4)2 and other related M(I)M(III)(SO4)2 Structures. The infrared and Raman spectra of powdered CsV(SO4)2 show close analogy to those of KV(SO4)2. The crystal Raman spectra show vibrational bands the polarization properties of which cannot be explained in terms of the crystallographic point group and a totally symmetric electronic ground state. Above 1300 cm-1 the Raman spectra, particularly at lower temperatures, show a coarse structure, which is interpreted as electronic Raman transitions between the spin-orbit split states of the A-3(g) and E-3(g) levels.