Electron-transfer reactions of uranium(V): kinetics of the uranium(V)-uranium(VI) self-exchange reaction

Luminescence spectrum of uranyl(V) in 2-propanol perchlorate solution

“…It shows that with increasing the irradiation times, uranium(VI) becomes reduced to uranium(V), and a respective U(V) absorption peak at 255 nm starts to grow. This is in agreement with earlier findings [5]. No absorption was observed between 380 and 450 nm, typical for U(VI); and 600-700 nm indicative for U(IV).…”

“…U(V) absorption studies have been conducted in the Vis and NIR regions and herein absorption peaks at approximately 770, 960, and 1500 nm are reported [1][2][3][4]. However, the highest extinction coefficient for uranium(V) is realized with an excitation at 255 nm [5] which is between the optimal excitation wavelengths for U(IV) at 245 nm [6] and U(VI) at 266 nm [7]. Absorption studies of tetravalent, pentavalent, and hexavalent uranium in solution have been performed by numerous scientists.…”

“…This is related to the fact that uranium(V) is unstable in solution due to disproportionation to uranium(IV) and uranyl(VI) species [9 and reference therein]. Aqueous U(V) species are only stable in a very narrow pH range (pH 2-3) and only for a short time of approximately 1 h [5]. In addition, the only known stable uranyl(V) complex is a carbonate species formed in basic aqueous solution (pH > 11) (e.g.…”

“…To our knowledge no luminescence of pentavalent uranyl in solution has been reported so far. This paper reports the first observation of luminescence of U(V) in solution.U(V) sample solutions were prepared by following a procedure described by Howes et al [5]. A solution containing 4 · 10 À4 M uranium(VI), 0.2 M NaClO 4 and 0.5 M 2-propanol at pH 2.41 ± 0.1 (HClO 4 = 2 mM) was irradiated with a mercury-vapour lamp (k max = 254 nm; LOT-Oriel) for 3-10 min.…”

A theoretical study of the qualitative reaction mechanism for the homogeneous disproportionation of pentavalent uranyl ions

“…The free energy differences are much larger than the similar studies seen on U(VI) to U(V) ET reactions. (Howes et al, 1988) Finally, all of the pathways are diabatic (small V AB ) due to the hydrogenbonded character of the complex and the distance between the donor and acceptor uranium atoms. Table 2b displays the analogous information using the MP2 gas phase energies in place of HF.…”