Exafs sur des composés de coordination de l'uranium en phase solide et en solution

Charpin, P.; Déjean, Alain; Folcher, G.; Rigny, Paul; Navaza, P.

doi:10.1051/jcp/1985820925

Cited by 28 publications

(20 citation statements)

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“…Recently, a few groups have provided a much more complete characterization of Np VII complexes, both in the solid state and alkaline solution. [91,94,115Ϫ117] In the solid state, current XAFS [91] and single-crystal diffraction studies support the original Russian results, finding the tetraoxo configuration in the highly alkaline solutions (Ͼ 4  OH Ϫ ) that stabilize this Ϫ d [99] Ϫ e,i [103] Ϫ f [104] Ϫ g [67] Ϫ h [105] Ϫ j [106] Ϫ k [107] Ϫ l [108] Ϫ # this work (#1 in 0.1  HClO 4 ; #2 in 0.1  HNO 3 ); (b) neptunium: the horizontal line represents the border between the Np V /Np VI domains: m [109] Ϫ n [105] Ϫ o,q [60] Ϫ p [110] Ϫ r [94] Ϫ # this work (0.01  in HClO 4 ); (c) plutonium: the horizontal line represents the border between the Pu V /Pu VI domains; s,u [111] Ϫ t,v [42] high oxidation state and in crystals of Co(NH 3 ) 6 NpO 4 (OH) 2 ·2H 2 O grown from this medium. In this compound, the four NpϭO oxo bonds expand to 1.85Ϫ1.90 Å , ca.…”

Section: Aqueous Actinyl Cationsmentioning

confidence: 59%

Investigating Actinyl Oxo Cations by X‐ray Absorption Spectroscopy

et al. 2003

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Early actinide elements (from U to Am) have the ability to form linear trans-dioxo complexes with formal valence of the actinide being equal to (V) or (VI). For instance, the ubiquity of the uranyl cation in uranium aqueous chemistry is the basis for its very important industrial and environmental concerns. As a result, the physical chemistry of the actinyl moieties has been the subject of constantly growing investigations. Among all the spectroscopic probes, X-ray absorption spectroscopy is a particularly useful element and energy-selective technique. This article reviews the investigation of molecular actinyl complexes using both XANES and EXAFS tools. The absorption edge features have long been used to characterize the frontier orbitals of the absorbing atom. In the case of actinide cations, the L III edge, located in the hard X-ray region, provides a useful fingerprint of the cation polyhedron. Tentatively, simple molecular orbital considerations together with full multiple scattering simulation codes have MICROREVIEWS: This feature introduces the readers to the author's research through a concise overview of the selected topic. Reference to important work from others in the field is included. Complementary structural data can be obtained in the EXAFS region of the absorption spectrum. In the literature, such molecular systems have been well documented from uranyl aqueous chemistry to neptunyl or plutonyl coordination complexes with oxygen donor ligands. Furthermore, complexation mechanisms upon absorption onto mineral surfaces have been increasingly investigated over the past few years. Overall, contribution of the XAS technique to a better understanding of the actinide bonding is demonstrated from various examples of the literature and the authors' data. Importance of the simulation codes in order to better describe the absorption features is also strongly underlined.

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Section: Aqueous Actinyl Cationsmentioning

confidence: 59%

Investigating Actinyl Oxo Cations by X‐ray Absorption Spectroscopy

et al. 2003

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“…The Fourier transforms (FTs) represent a pseudo-radial distribution function of the uranium near-neighbor environment, and the peaks appear at lower R values relative to the true near neighbor distances as a result of the electron scattering phase shifts which are different for each neighboring atom (a = 0.2-0.5 A). The FTs illustrate that the EXAFS spectra are dominated by backscattering from the Ο atoms of the linear υθ| + group (peak at 1.30 A) [26][27][28][29][30], Backscattering from the Ο atoms lying in the equatorial plane of the UC>2 + ion is observed in the pH-7 and schoepite data sets as shown by the pattern of FT peaks centered around 1.90 A. Moving from pH-7 to pH-11, a structural transformation is observed in the precipitates as the 1.30 A peak broadens, shifts to higher R, and the pattern in the equatorial Ο region is lost.…”

Section: Exafs and Ftir Data Acquisitionmentioning

confidence: 99%

Determinations of Uranium Structures by EXAFS: Schoepite and Other U(VI) Oxide Precipitates

et al. 1996

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We have investigated the structures of U(VI) oxides precipitated from room temperature aqueous solutions at low ionic strength as a function of pH. Using the uranium Lm-edge extended Xray absorption fine structure (EXAFS) and infrared (IR) spectroscopies as probes of the local structure around the uranium, a trend is observed whereby the axial oxygen bond lengths from the uranyl groups increase from 1.80 A at pH = 7 to 1.86 A at pH = 11. Shifts in the IR spectral frequencies support this assignment. A concomitant decrease in the equatorial oxygen and nearest-neighbor uranium bond lengths also occurs with increasing pH. Expansion of the linear 0=U=0 group is seen directly at the L m absorption edge where multiple scattering resonances systematically shift in energy. EXAFS curve-fitting analysis on these precipitates and a sample of synthetic schoepite indicate that the structure of the species formed at pH = 7 is similar to the structure of schoepite. At pH = 11, the precipitate structure is similar to that of a uranate.

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“…As in U(V1) solids, the basic structural moiety of aqueous U(VI) is uranyl (Karim et al, 1980;Charpin et al, 1985;Chisholm-Brause et al, 1992;Dent et al ., 1992). Four to six ligands are arranged in a planar equatorial fashion around the uranium atom (GorllerWalrand and Colen, 1982;Charpin et al, 1985).…”

Section: Aqueous Solution Chemistrymentioning

confidence: 99%

“…Four to six ligands are arranged in a planar equatorial fashion around the uranium atom (GorllerWalrand and Colen, 1982;Charpin et al, 1985). In low ionic strength aqueous solution under oxidizing conditions, 0 atoms tend to occupy the equatorial positions immediately adjacent to U.…”

Section: Aqueous Solution Chemistrymentioning

confidence: 99%