POLARIZED XANES AND EXAFS AT THE V-K-EDGE OF VOPO4.2H2O GEL, COMPARISON WITH THE V-K-EDGE IN V2O5 XEROGEL

Coatings have been obtained by deposition of colloidal solutions of VO PO4 and V2O5 onto a flat substrate. The strong pre-edge anisotropy of these materials reveals a good texturation and organization of these g els even at the molecular scale. Using EXAFS on V2O5 single crystal an d VOPO4 layers, we deduce first that the short axial bond lengths are the same in both compounds, and second that pre-edge can be used even on powders to track any change in axial bonds. Comparing polarized XAN ES and crystallographic structures, we show that it is a sensitive pro be, allowing one to detect weak asymmetries in the ligand coordination sphere. However, the lack of theoretical basis of this effect prevent s any quantitative estimate.