Investigation of charge-transfer absorptions in the uranyl UO22+(VI) ion and related chemical reduction of UO22+(VI) to UO2+(V) by UV–Vis and electron paramagnetic resonance spectroscopies

Abstract

a b s t r a c tThe uranyl UO 2 2+ (VI) cation (hydrated) exhibited strong charge-transfer absorptions at 350-400 nm in aqueous solutions containing bromide and iodide. The charge-transfer absorptions originate from a single-electron transfer from a halide anion to the uranium(VI) valence shell. Their intensities (represented by absorbance at 375 nm) were found to be directly proportional to molar concentrations of the halide (bromide or iodide) and UO 2 2+ in solution, respectively, showing the nature of a bimolecular interaction in the charge-transfer absorption transition. The absorptions were also greatly enhanced by sulfuric acid, and their intensity (absorbance at 375 nm) increased linearly as a function of the acid molarity. An electron paramagnetic resonance (EPR) study has indicated that the charge-transfer also took place slowly in the dark, resulting in appreciable thermal chemical reduction of diamagnetic UO 2 2+ (VI) (hydrated) to paramagnetic UO 2 + (V) (hydrated) (g = 2.08) by bromide and iodide. In the presence of sulfuric acid, CH 3 SOCH 3 (DMSO) was shown by EPR to undergo a charge-transfer oxidation by UO 2 2+(VI) to a stable CH 3 SOCH 2 Å (DMSO Å ) radical (singlet, g = 2.01), and UO 2 2+ (VI) was reduced to UO 2 + (V). A possible mechanism for this oxidation-reduction has been proposed. The charge-transfer absorption transition (350-400 nm) between UO 2 2+ (VI) and phenol (PhOH) in acetone was observed and characterized. A chemical oxidation-reduction of UO 2 2+ (VI) [in the form of U VI O 2 (acetone) 5 2+] and PhOH in acetone was found by EPR to give UO 2 + (V) [in the form of U V O 2 (acetone) 5 + ] and a stable phenoxyl (PhO Å ) radical (singlet, g = 2.00) via a simultaneous charge-transfer and deprotonation pathway.

f‐block MOFs: A Pathway to Heterometallic Transuranics

“…In particular, we monitored the rate of the U→Th conversion spectrophotometrically through analysis of the supernatant solution. As shown in Figure 2, the intensity of the absorption bands at λ max =424 nm, associated with the UO 2 2+ π–π* transitions, [59–61] increased over time, which is consistent with the increased concentration of UO 2 2+ as transmetallation progresses.…”

Зондовая Спектроскопия Комбинационного Рассеяния Света Поликристаллов Ураниловых Соединений

“…Присутствие соответствующего комбинационного сателлита в спектрах КР анализируемых веществ может служить надeжным индикатором иона уранила. Практическое использова-ние метода спектроскопии КР до последнего времени было затруднено [4][5][6][7] в связи с необходимостью использования громоздкого оборудования в виде двойного или тройного монохроматоров и высокочувствительного одноканального приeмника излучения -фотоумножителя [8][9][10]. При этом удавалось осуществлять регистрацию спектра КР при большом времени экспозиции и для достаточно большого количества исследуемого вещества.…”