Vibrational Spectroscopy of Mass Selected [UO2(ligand)n]2+ Complexes in the Gas Phase
The gas-phase infrared spectra of discrete uranyl ([UO2]2+) complexes ligated with acetone and/or acetonitrile were used to evaluate systematic trends of ligation on the position of the O=U=O stretch, and to enable rigorous comparison with the results of computational studies. Ionic uranyl complexes isolated in a Fourier transform ion cyclotron resonance mass spectrometer were fragmented via infrared multiphoton dissociation using a free electron laser scanned over the mid-IR wavelengths. The asymmetric O=U=O stretching frequency was measured at 1017 cm-1 for [UO2(CH3COCH3)2]2+, and was systematically red shifted to 1000 and 988 cm-1 by the addition of a third and fourth acetone ligands, respectively, which was consistent with more donation of electron density to the uranium center in complexes with higher coordination number. The experimental measurements were in good agreement with values generated computationally using LDA, B3LYP, and ZORA-PW91 approaches. In contrast to the uranyl frequency shifts, the carbonyl frequencies of the acetone ligands were progressively blue shifted as the number of ligands increased from 2 to 4, and approached that of free acetone. This observation was consistent with the formation of weaker noncovalent bonds between uranium and the carbonyl oxygen as the extent of ligation increases. Similar trends were observed for [UO2(CH3CN)n]2+ complexes although the magnitude of the red shift in the uranyl frequency upon addition more acetonitrile ligands was smaller than for acetone, consistent with the more modest nucleophilic nature of acetonitrile. This conclusion was amplified by the uranyl stretching frequencies measured for mixed acetone/acetonitrile complexes, which showed that substitution of one acetone for one acetonitrile produced a modest red shift of 3 to 6 cm-1.
- Research Organization:
- Idaho National Laboratory (INL)
- Sponsoring Organization:
- DOE - EM
- DOE Contract Number:
- AC07-99ID13727
- OSTI ID:
- 912416
- Report Number(s):
- INL/JOU-05-00908
- Journal Information:
- Journal Am. Chem. Soc., Journal Name: Journal Am. Chem. Soc. Journal Issue: 14 Vol. 128; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACETONE
ACETONITRILE
CARBONYLS
COORDINATION NUMBER
DISSOCIATION
ELECTRON DENSITY
FREE ELECTRON LASERS
INFRARED SPECTRA
ION CYCLOTRON-RESONANCE
MASS SPECTROMETERS
OXYGEN
RED SHIFT
SPECTROSCOPY
UO2 ligands
URANIUM
URANYL COMPLEXES
WAVELENGTHS
gas-phase
vibrational spectroscopy