Infrared Spectroscopy of Dioxouranium (V) Complexes with Solvent Molecules: Effect of Reduction
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 ?m region of the infrared spectrum. Antisymmetric O=U=O stretching frequencies (?3) 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 ?3 value equal to that of the n-PrOH-containing complex. The ?3 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 ?* orbitals of the uranyl moiety. Computational modelling of the ?3 frequencies of these species using PBE, B3LYP and LDA functionals showed good agreement with the IRMPD measurements. In general, expected trend in ?3 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 ?3 absorptions in the MeOH and EtOH complexes.
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC07-99ID-13727
- OSTI ID:
- 936871
- Report Number(s):
- INL/JOU-08-13725; CPCHFT; TRN: US0805719
- Journal Information:
- ChemPhysChem, Vol. 9, Issue 9; ISSN 1439-4235
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALCOHOLS
ELECTRON DENSITY
FREE ELECTRON LASERS
FUNCTIONALS
ION CYCLOTRON-RESONANCE
IONIZATION
MASS SPECTROMETERS
SIMULATION
SOLVENTS
SPECTROSCOPY
Infrared multiple photon dissociation spectroscop
Density Functional Theory
IRMPD
uranium
uranyl coordination complex