HIGH-TEMPERATURE NMR-STUDIES OF THE GLASS-CRYSTAL TRANSITION IN THE CS2S2O7-V2O5 SYSTEM

Cs-133 NMR and 2D-EXSY NMR and V-51 NMR spectra have been recorded of CS2S7O7 and of the catalytically important Cs2S2O7-V2O5 mixtures in th e temperature range 20-550 degrees C, covering both the solid and liqu id region. A high mobility of the Cs+ cations in Cs2S2O7 was observed below the melting point (461 degrees C), and two crystalline modificat ions seem to be present depending on the method of preparation of CS2S 2O7 Cs-133 and V-51 NMR spectra of the Cs2S2O7-V2O5 mixtures with the molar composition Cs/V = 2 and 4 show, by heating from room temperatur e, in both cases, that the glassy samples transform to crystalline Cs- 4(VO)(2)O(SO4)(4) around 220 degrees C and that further heating of the samples up to the melting point leads to a mobility of the Cs cations similar to what was found for Cs2S2O7 For a sample with the compositi on Cs/V = 1 a similar transformation from a glassy state at around 250 degrees C is observed; however, here the possible compound CsVO2SO4 s eems to be transformed to another crystalline modification by heating to 400 degrees C. At 550 degrees C in the molten state the V-51 NMR sp ectra indicate that the coordination of vanadium changes from distorte d octahedral in the solid to tetrahedral in the liquid state.