Direct evidence of uranium(V) intermediates by electron spin resonance in photo- and electrolytic reduction processes of uranyl complexes in organic solutions

Pentavalent uranium chemistry—synthetic pursuit of a rare oxidation state

“…Figure 31 shows a representative plot of XT versus T and X versus T for a U V ion. 25 Effective magnetic moments in the range of 2.03-2.65 JiB/U were observed for these compl exes with no significant differences in Jieff values or temperature dependencies based on XIY (Tab le 3). At this point, uranium(V) magnetism U V deserves some special attention.…”

“…From a structural perspective, the complexes all contain flexible a-In-donor ligands that can act as a buffer to accommodate the needs of the uranium metaL The ability of 20 these N(amide), O(.lkoxide), P(phosphine), S('hiola,e) and C(carbocycle) donors, along with even the uranyl and imido fragments, to adjust their electron-donating abil ity in response to the e lectronic demands of the uran ium metal appears vita l to the isolation and stability of the resultant pentavalent complexes. 25 And yet, even with all the synthetic advances made toward U V systems over recent years, compared to the other uranium oxiqation states (III, IV , VI), there is still so much that we do not understand abo ut this en igmatic oxidation state. The dearth of available physical characterization data for 30 molecular uranium(V) systems is a genera l problem in the field.…”

“…Electron paramagnetic resonance (EPR) spectroscopy was used to measure the products of the photo-and electrolytic reduction 10 of the complexes U V '02(LMCI0 4 h (L = dimethylformamide (DMF) (1), dimethylsulfoxide (DMSO) (2), triethylphosphate (TEP) (3)) and U V 'OiLMN0 3 )2 (L = DMF (4), DMSO (5), TEP (6). 25. 26 The optical spectra measured in the reductions of these complexes indicated the formation of uranium(V) 15 with Amax at 770, 970 and 1400 nm.…”

“…Much of the early work in the 45 field was directed towards finding volatile materials to be used in uranium isotope separations, but those attempts were unsuccessful due to the chronic instability and decomposition of homoleptic alkyls. 25 comprised of both Sf n (SI %) and Sf" (39%). The principle complex by adventitious traces of air.…”

“…Generally speaking, aside 25 from classical coordination complexes of the halides such as UOX/-, UXs and UX 6 -(X = halide), rational synthetic schemes were simply unknown and the few reported molecular U V systems came from serendipitous discoveries that were not reproduci ble. As a consquence, very little was )0 known about pentavalent uranium; most of our existing knowledge about the physicochem ical properties associated with this oxidation state has come from halide coordination complexes and was captured in the last comprehensive review on uranium(V) in 1969 2 35 In recent years, the abil ity to access U V systems has become more prevalent.…”