X-ray Absorption Spectroscopy of Tricarbonatodioxouranate(V), [UO₂(CO₃)₃]^5-, in Aqueous Solution

Abstract

Actinyl ions (AnO(2)(+) and AnO(2)(2+)) are strongly complexed by CO(3)(2)(-) in aqueous solution, and tricarbonato complexes of UO(2)(2+) and NpO(2)(+), in particular, have been widely studied. Cyclic voltammetry shows that, whereas the Np(V)/Np(VI) couple is reversible in aqueous CO(3)(2)(-) solution, the analogous U couple is irreversible, suggesting significant conformational change on one-electron reduction of [UO(2)(CO(3))(3)](4)(-). EXAFS spectroscopy has been used to define the coordination geometry of the reduced species and shows that both axial and equatorial U-O distances increase on reduction, from 1.80 to 1.90 Å and from 2.43 to 2.50 Å, respectively. The basic geometry of the U complex is apparently unchanged by reduction so any conformational change which does occur must be subtle.

An in-situ X-ray absorption spectroelectrochemical study of the electroreduction of uranium ions in HCl, HNO3, and Na2CO3 solutions

“…The edge jump slightly shifted from 17.164 to 17.163 keV (Figure 10), and the spectra were similar to those reported previously [15,16]. The solution was light yellow before the electrolysis and colorless and transparent afterwards, which is typical of Table 1) [15,16,47]. The fits are shown as dashed lines in Figure 11a and b, and these results agree with the previous reports [15,16].…”

“…The solution was light yellow before the electrolysis and colorless and transparent afterwards, which is typical of Table 1) [15,16,47]. The fits are shown as dashed lines in Figure 11a and b, and these results agree with the previous reports [15,16]. The electrode potential of − 0.95 V was high enough to form UO …”

“…To prepare the reduced products, electrochemical bulk electrolysis was combined with UV-Visible spectroscopy or XAFS measurements of UO + 2 [14][15][16][17] and U…”

Uranium triatomic compounds XUY (X,Y=C,N,O): a combined multiconfigurational second-order perturbation and density functional study

“…This error is entirely recovered in the CASPT2-lg calculation. B3LYP is less accurate in determining the higher frequency for [28].) A CASPT2 study on UO2 2 complexes is currently going on [29], and preliminary results show that CASPT2 with an ANO-S basis (thus comparable to our CASPT2-s results) predicts a U±O bond distance which is ca 1±2% longer than experiment.…”

Soil Humic Acid Decreases Biological Uranium(VI) Reduction by Shewanella putrefaciens CN32

“…If this mechanistic pathway of U(VI) bioreduction is correct, it is possible that humic materials could stabilize {UO 2 ϩ } and interfere with further reduction. Previous XAFS studies of U(V) have found U-Oaxial and U-Oequitorial distances of 1.90 Ϯ 0.02 and 2.50 Ϯ 0.02 Å, respectively (Docrat et al, 1999). Fits to first coordination shell phase components of the XAFS data from samples from this study indicate U-Oaxial distances of 1.74-1.81 Å and U-Oequitorial distances of 2.35-2.38 Å.…”