Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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On the use of HERFD-XANES at the U L3 and M4-edges to determine the uranium valence state on [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3]
Bès, R.; Rivenet, M.; Solari, P. L.; Kvashnina, K. O.; Scheinost, A. C.; Martin, P. M.;
We report and discuss here the unambiguous uranium valence state determination on the complex compound [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] by using High Energy Resolution Fluorescence Detection - X-ray Absorption Near Edge Structure spectroscopy (HERFD-XANES). The spectra at both uranium L3- and M4-edges confirm that all the five non-equivalent uranium atoms are solely in the hexavalent form in this compound, as previously suggested by Bond Valence Sum analysis and X-ray diffraction pattern refinement. Moreover, the presence of the pre-edge feature, due to the 2p3/2-5f quadrupole transition, has been observed in the U L3-edge HERFD-XANES spectrum, in agreement with theoretical and experimental observations of other uranium based compounds. Recently, this feature has been proposed as a possible tool to determine the uranium oxidation state in a manner similar to 3d and 4d metals. Nevertheless, this feature is also very sensitive to the uranium local environment, as revealed by our theoretical calculations, and consequently could not be used to attribute without ambiguity the uranium valence state. In contrast, U M4-edge HERFD-XANES appears to be the most straightforward and reliable way to assess uranium valence state in very complex materials such as [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] or mixture of compounds.
Keywords: XANES XES HERFD uranium oxidation state

Publ.-Id: 22844 - Permalink