Synthesis and Vibrational Identification of the Uranyl Peroxodicarbonate [UO2(O2)(CO3)3]4-: Insights into Peroxo-Carbonate Bonding from 18O Labeling, DFT and QTAIM analysis
Year: 2026
Type: preprint
Abstract: In carbonate-rich aqueous environments relevant to spent nuclear fuel storage, the coexistence of carbonate species and radiolytically generated H 2 O 2 is expected to promote the formation of uranyl peroxo-carbonate complexes under mild conditions. Despite their importance, reliable vibrational markers for uranyl peroxo-carbonate complexes remain scarce, and several reported spectral assignments remain controversial. Here, we report the first unambiguous solution-phase characterization of the peroxo-dicarbonate species M x [UO 2 (O 2 )(CO 3 ) 2 ] (4-x)- (M = Na + or K + ) by combining Raman spectroscopy with 18 O-labeled H 2 O 2 , Fourier-transform infrared (FTIR) spectroscopy, and density functional theory (DFT) calculations. Distinct vibrational fingerprints are identified for M x [UO 2 (O 2 )(CO 3 ) 2 ] (4-x) and are clearly differentiated from those of the triscarbonate complex [UO 2 (CO 3 ) 3 ] 4- . Key Raman bands of the peroxo-dicarbonate complex include the ν s (U-O yl ) stretch at 765-769 cm −1 , the v 1 (U-O peroxo ) mode at 418-440 cm −1 , and the v 1 (O-O) stretch at 845-850 cm −1 , the latter exhibiting a pronounced isotopic shift upon 18 O substitution. Complementary FTIR measurements reveal weak absorptions near 425, 765 and 865 cm −1 attributed to v1(U-O peroxo ), ν s (U-O yl ) and v 1 (O-O), respectively, providing the first infrared evidence of a uranyl peroxo-carbonate complex in aqueous solution. DFT calculations reproduce the observed frequencies and isotope shifts, clarifying the role of solvation and counter-cation effects. These results resolve long-standing ambiguities in uranyl peroxo-carbonate speciation and establish a robust spectroscopic framework relevant to uranium fuel dissolution, environmental mobility, and long-term waste stability.
Source: ChemRxiv
Language: English
Subfield: Inorganic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7129045942