ChemInform Abstract: In situ Laser Raman Spectroscopy Studies of the Transformation of VOHPO4×0.5H2O and (VO)2P2O7.

A detailed study of three samples of vanadyl hemihydrate, VOHPO4·0.5H2O, and vanadyl pyrophosphate, (VO)2P2O7, prepared using different methods is described and discussed. VOHPO4·0.5H2O, prepared using (a) the VPA method (V2O5 and H3PO4 refluxed in aqueous HCl), (b) the VPO method (V2O5 and H3PO4 refluxed in isobutanol) and (c) the VPD method (VOPO4·2H2O refluxed in isobutanol), is readily converted to (VO)2P2O7 by heating in an inert gas at 750–775°C. The three samples of (VO)2P2O7 have significant differences in the P–O–P stretch region of the Raman spectra and also exhibit marked differences in their reactivity with oxygen, although the powder X-ray diffraction patterns for the three samples are identical. The VPA-derived (VO)2P2O7 is readily oxidised at 400°C, whereas the VPO-derived (VO)2P2O7 is particularly unreactive. The oxidation/reduction transformations are studied using in situ laser Raman spectroscopy and temperature programmed oxidation and it is shown that the oxidation/reduction process can be cycled many times and the morphology of the crystallite remains unchanged.