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Title: Vibrational Spectroscopy of Mass-Selected [UO₂(ligand)n]²⁺ Complexes in the Gas Phase: Comparison with Theory

Abstract

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 ligand, respectively, which was consistent with increased donation of electron density to the uranium center in complexes with higher coordination number. The values generated computationally using LDA, B3LYP, and ZORA-PW91 were in good agreement with experimental measurements. 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⁺more » complexes, although the magnitude of the red shift in the uranyl frequency upon addition of more acetonitrile ligands was smaller than for acetone, consistent with the more modest nucleophilic nature of acetonitrile. This conclusion was confirmed 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.« less

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
882964
Report Number(s):
PNNL-SA-47739
9598; KP1704020
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society, 128(14):4802-4813
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Groenewold, G. S., Gianotto, Anita K., Cossel, Kevin C., Van Stipdonk, Michael J., Moore, David T., Polfer, Nick, Oomens, Jos, De Jong, Wibe A., and Visscher, Lucas. Vibrational Spectroscopy of Mass-Selected [UO₂(ligand)n]²⁺ Complexes in the Gas Phase: Comparison with Theory. United States: N. p., 2006. Web. doi:10.1021/ja058106n.
Groenewold, G. S., Gianotto, Anita K., Cossel, Kevin C., Van Stipdonk, Michael J., Moore, David T., Polfer, Nick, Oomens, Jos, De Jong, Wibe A., & Visscher, Lucas. Vibrational Spectroscopy of Mass-Selected [UO₂(ligand)n]²⁺ Complexes in the Gas Phase: Comparison with Theory. United States. doi:10.1021/ja058106n.
Groenewold, G. S., Gianotto, Anita K., Cossel, Kevin C., Van Stipdonk, Michael J., Moore, David T., Polfer, Nick, Oomens, Jos, De Jong, Wibe A., and Visscher, Lucas. Sat . "Vibrational Spectroscopy of Mass-Selected [UO₂(ligand)n]²⁺ Complexes in the Gas Phase: Comparison with Theory". United States. doi:10.1021/ja058106n.
@article{osti_882964,
title = {Vibrational Spectroscopy of Mass-Selected [UO₂(ligand)n]²⁺ Complexes in the Gas Phase: Comparison with Theory},
author = {Groenewold, G. S. and Gianotto, Anita K. and Cossel, Kevin C. and Van Stipdonk, Michael J. and Moore, David T. and Polfer, Nick and Oomens, Jos and De Jong, Wibe A. and Visscher, Lucas},
abstractNote = {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 ligand, respectively, which was consistent with increased donation of electron density to the uranium center in complexes with higher coordination number. The values generated computationally using LDA, B3LYP, and ZORA-PW91 were in good agreement with experimental measurements. 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 of more acetonitrile ligands was smaller than for acetone, consistent with the more modest nucleophilic nature of acetonitrile. This conclusion was confirmed 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.},
doi = {10.1021/ja058106n},
journal = {Journal of the American Chemical Society, 128(14):4802-4813},
number = ,
volume = ,
place = {United States},
year = {Sat Mar 18 00:00:00 EST 2006},
month = {Sat Mar 18 00:00:00 EST 2006}
}
  • 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 OdUdO 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 OdUdO 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 acetonemore » ligand, respectively, which was consistent with increased donation of electron density to the uranium center in complexes with higher coordination number. The values generated computationally using LDA, B3LYP, and ZORA-PW91 were in good agreement with experimental measurements. 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 two to four 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 uranyl asymmetric stretching frequencies were greater than those measured for acetone complexes having equivalent coordination, which is consistent with the fact that acetonitrile is a weaker nucleophile than is acetone. This conclusion was confirmed 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 3-6 cm-1.« less
  • 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 acetonemore » 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.« less
  • Experiments have been undertaken to record photofragmentation spectra from a series of [Ag(L){sub N}]{sup 2+} complexes in the gas phase. Spectra have been obtained for silver(II) complexed with the ligands (L): acetone, 2-pentanone, methyl-vinyl ketone, pyridine, and 4-methyl pyridine (4-picoline) with N in the range of 4-7. A second series of experiments using 1,1,1,3-fluoroacetone, acetonitrile, and CO{sub 2} as ligands failed to show any evidence of photofragmentation. Interpretation of the experimental data has come from time-dependent density functional theory (TDDFT), which very successfully accounts for trends in the spectra in terms of subtle differences in the properties of the ligands.more » Taking a sample of three ligands, acetone, pyridine, and acetonitrile, the calculations show all the spectral transitions to involve ligand-to-metal charge transfer, and that wavelength differences (or lack of spectra) arise from small changes in the energies of the molecular orbitals concerned. The calculations account for an absence in the spectra of any effects due to Jahn-Teller distortion, and they also reveal structural differences between complexes where the coordinating atom is either oxygen or nitrogen that have implications for the stability of silver(II) compounds. Where possible, comparisons have also been made with the physical properties of condensed phase silver(II) complexes.« less
  • Wavelength-selective infrared multiple photon photo-dissociation (IRMPD) was used to generate infrared spectra of anionic nitrate complexes of UO₂²+ and Eu3+ in the mid-infrared region. A pattern of absorptions were observed for both species, including splitting of the antisymmetric O-N-O stretch into high and low frequency components with the magnitude of the splitting consistent with attachment of nitrate to a strong Lewis acid center. The frequencies measured for [UO2(NO3)3]- were within a few cm-1 of those measured in the condensed phase, the best agreement yet achieved for a comparison of IRMPD with condensed phase absorption spectra. In addition, experimentally-determined values weremore » in good general agreement with those predicted by DFT calculations, especially for the antisymmetric UO₂ stretch. The spectrum from the [UO₂ (NO₃)₃]- was compared with that of [Eu(NO3)4]-, which showed that nitrate was bound more strongly to the Eu3+ metal center, consistent with its higher charge. The spectrum of a unique uranyl-oxo species having an elemental composition [UO9N₃]- was also acquired, for which calculations suggested a [UO₂(NO₃)₂(O)]- structure.« less
  • The intrinsic binding of halide ions to the metal center in the uranyl molecule is a topic of ongoing research interest in both the actinide separations and theoretical communities. Investigations of structure in the condensed phases is frequently obfuscated by solvent interactions that can alter ligand binding and spectroscopic properties. The approach taken in this study is to move the uranyl halide complexes into the gas phase where they are free from solvent interactions, and then interrogate their vibrational spectroscopy using infrared multiple photon dissociation (IRMPD). The spectra of cationic coordination complexes having the composition [UO₂(X)(ACO)₃] + (where X =more » F, Cl, Br and I; ACO = acetone) were acquired using electrospray for ion formation, and monitoring the ion signal from the photoelimination of ACO ligands. The studies showed that the asymmetric ν₃ UO₂ frequency was insensitive to halide identity as X was varied from Cl to I, suggesting that in these pseudo-octahedral complexes, changing the nucleophilicity of the halide did not appreciably alter its binding in the complex. The ν₃ peak in the spectrum of the F-containing complex was 9 cm -1 lower indicating stronger coordination in this complex. Similarly the ACO carbonyl stretches showed that the C=O frequency was relatively insensitive to the identity of the halide, although a modest shift to higher wavenumber was seen for the complexes with the more nucleophilic anions, consistent with the idea that they loosen solvent binding. Surprisingly, the ν1 stretch was activated when the softer anions Cl, Br and I were present in the complexes. IR studies of the anionic complexes [UO₂X₃] - (where X = Cl -, Br - and I -) compared the ν₃ UO₂ modes versus halide, and showed that the ν₃ values decreased with increasing anion nucleophilicity. This observation was consistent with DFT calculations that indicated that [UO₂X₂] --X ∙ and [UO₂X₂]∙-X - dissociation energies decreased on the order F > Cl > Br > I. The trifluoro complex could not be photodissociated in these experiments.« less