title: 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].
abstract: 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 U L3- and M4-edges confirm that all five nonequivalent U 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 preedge 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 that of 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 the uranium valence state in very complex materials such as [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] or a mixture of compounds.
authors.affiliation: Synchrotron SOLEIL, Ligne de lumière MARS , L'Orme des Merisiers, Saint Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex, France.|CEA, DEN, DEC, Centre d'études nucléaires de Cadarache , F-13108 Saint Paul Lez Durance, France.
authors.forename: René
authors.initials: R
authors.lastname: Bès
authors.affiliation: Université Lille, CNRS, Centrale Lille, ENSCL, Université Artois, UMR 8181, UCCS, Unité de Catalyse et Chimie du Solide , F-59000 Lille, France.
authors.forename: Murielle
authors.initials: M
authors.lastname: Rivenet
authors.affiliation: CEA, DEN, DEC, Centre d'études nucléaires de Cadarache , F-13108 Saint Paul Lez Durance, France.
authors.forename: Pier-Lorenzo
authors.initials: PL
authors.lastname: Solari
authors.affiliation: Rossendorf Beamline (ROBL) at the European Synchrotron Radiation Facility (ESRF), CS40220 , F38043 Grenoble, France.|Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology , P.O. Box 510119, 01314 Dresden, Germany.
authors.forename: Kristina O
authors.initials: KO
authors.lastname: Kvashnina
authors.affiliation: Rossendorf Beamline (ROBL) at the European Synchrotron Radiation Facility (ESRF), CS40220 , F38043 Grenoble, France.|Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology , P.O. Box 510119, 01314 Dresden, Germany.
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Scheinost
authors.affiliation: CEA, DEN, DTEC, Centre d'études nucléaires de Marcoule , Bagnols-sur-Cèze F-30207, France.
authors.forename: Philippe M
authors.initials: PM
authors.lastname: Martin