XAS study of actinide and lanthanide solvent extraction compounds—I. UO2(NO3)2(TIBP)2 and UO2(NO3)2(TBP)2 (with TIBP = tri-isobutylphosphate and TBP = tributylphosphate)

Investigating Actinyl Oxo Cations by X‐ray Absorption Spectroscopy

“…Decrease of the DebyeϪWaller factors upon temperature drop may also account for differences on the FT although data fitting has not shown any significant trend in this particular case. [85] The best fit results exhibit a nonsignificant expansion (ϩ 0.01 Å ) of the equatorial UϪO bond lengths from 77 to 298 K. At the same temperature, the solid-state and solution complexes are similar from the EXAFS point of view with 2 axial O at 1.77 Å , 2 equatorial O(phosphate) at 2.40 Å and 4 equatorial O(nitrate) at 2.54 Å . From U to Pu, no significant evolution of the coordination sphere can be observed.…”

“…Calculations have been carried out on a pentagonal bipyramid cluster using self-consistency methods and muffin tin potentials, but without taking into account any sol- Figure 2. Experimental L III edges of UO 2 2ϩ (solution in perchloric acid [84] ), NpO 2 2ϩ (solution in perchloric acid), PuO 2 2ϩ [solution of PuO 2 (NO 3 ) 2 TBP 2 in TBP [85] ] and AmO 2 ϩ [solid K 3 AmO 2 -(CO 3 ) 2 [86] ] (-); calculations (Feff-8.1) are compared to the experimental uranium edge: FMS (-), single scattering (Ϫ Ϫ ) and atomic absorption (----); the l ϭ 2 and l ϭ 3 projected DOS is also displayed on the same relative energy scale; all the experimental spectra have been shifted in energy with respect to the calculated uranium pentagonal bipyramid edge maximum vent effects. In addition, the l projected density of states (DOS) calculated with the same potentials but with no core hole, for l ϭ 2 and 3, are shown on the same relative energy scale.…”

“…[85,127] In comparison, the humic acids contain several of the above functional oxygen groups and are indeed among the most complex natural systems. Donor sites are therefore difficult to identify and alternate strategies as complexation by synthetic identified functional groups as xylose, phenylalanine or glycine are needed in order to understand the complex formation.…”

“…The quadratic dumping of the 4-leg multiple scattering path amplitude as well as the phase shift when the bond angle decreases can be used to extract bond angle information. [85] On Figure 8, comparison is made with the FT of both solid-state UO 2 (NO 3 ) 2 (TiBP) 2 at 298 K and UO 2 (N-O 3 ) 2 (TBP) 2 (TBP ϭ tributyl phosphate) in TBP solution at 298 K. Both liquid and solid-state complexes analyzed at room temperature exhibit the same FT, in particular in the multiple-scattering 2.5Ϫ4.5-Å region. However, discrepancies with the same solid-state complex analyzed at 77 K indicate that the conformation of the uranyl coordination sphere is temperature-dependent.…”

“…Few solid-state crystal structures have been published [133,134] with nitrate ligands. In Figure 9 (a,b), comparison between solid-state UO 2 (NO 3 ) 2 (TiBP) 2 [85] and UO 2 (NO 3 ) 2 (DBDMBA) 2 (N,N-dibutyl-dimethylbutaramide) [135] complexes shows minor differences. In the multiple scattering regime, peaks C, D and E are present with modulations compared to UO 2 (NO 3 ) 2 (TiBP) 2 because of differences in backscattering phases and amplitudes.…”