Infrared Spectroscopy of Dioxouranium (V) Complexes with Solvent Molecules: Effect of Reduction

Journal Article · Tue May 13 04:00:00 EDT 2008 · Chemphyschem, 9(9):1278-1285

DOI:https://doi.org/10.1002/cphc.200800034· OSTI ID:937025

Groenewold, G S; Van Stipdonk, Michael J; De Jong, Wibe A; Oomens, Jos; Gresham, Garold L; McIIwain, Michael E; Gao, Da; Siboulet, Bertrand; Visscher, Lucas; Kullman, Michael; Polfer, Nick

UO2+-solvent complexes having the general formula [UO₂ (ROH)]+ (R = H, CH₃, C₂H₅, and n-C₃H₇) were formed using electrospray ionization and stored in a Fourier transform ion cyclotron resonance mass spectrometer, where they were isolated by mass-to-charge ratio, and then photofragmented using a free electron laser scanning through the 10 μm region of the infrared spectrum. Antisymmetric O=U=O stretching frequencies (ν3) were measured for all four complexes, which ranged from ~ 953 cm¯¹ for H₂O to ~ 944 cm¯¹ for n- PrOH, with the value for the EtOH-containing complex intermediate, systematically decreasing with increasing nucleophilicity of the solvent. The value for the MeOH-containing did not follow the trend, and had a measured ν3 value equal to that of the n-PrOH-containing complex. The ν3 frequency values for these U(V) complexes are comparable to those for the anionic [UO₂ (NO₃)₃]- complex, and lower than previously reported values for ligated uranyl (VI) dication complexes by 40 – 70 cm¯¹, and cationic uranyl (VI) ion-pair complexes by 10 – 40 cm¯¹. The lower frequency is attributed to weakening of the O=U=O bonds by repulsion related to reduction of the U metal center, which increases electron density in the antibonding π* orbitals of the uranyl moiety. Computational modelling of the ν3 frequencies of these species using PBE, B3LYP and LDA functionals showed good agreement with the IRMPD measurements. In general, expected trend in ν3 frequencies expected for the H₂O – MeOH – EtOH – n-PrOH series was produced by all three computational methods, however the three alcohols produced very similar values. The inverted order of MeOH and EtOH was not directly accounted for by the models, but is probably the result of overlapping C-H wagging modes that shift the apparent maxima of the O=U=O ν3 absorptions in the MeOH and EtOH complexes.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 937025
• Report Number(s): PNNL-SA-58694; 9598; KC0302030
• Journal Information: Chemphyschem, 9(9):1278-1285, Journal Name: Chemphyschem, 9(9):1278-1285 Journal Issue: 9 Vol. 9; ISSN CPCHFT; ISSN 1439-4235
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
ELECTRONIC STRUCTURE
Environmental Molecular Sciences Laboratory
FREQUENCY DEPENDENCE
INFRARED SPECTRA
MOLECULAR MODELS
SOLVENTS
URANYL COMPLEXES