Infrared Spectroscopy of Discrete Uranyl Anion Complexes

Idaho National Laboratory, Idaho Falls, Idaho, USA.
The Journal of Physical Chemistry A (Impact Factor: 2.69). 02/2008; 112(3):508-21. DOI: 10.1021/jp077309q
Source: PubMed

ABSTRACT The Free-Electron Laser for Infrared Experiments (FELIX) was used to study the wavelength-resolved multiple photon photodissociation of discrete, gas-phase uranyl (UO22+) complexes containing a single anionic ligand (A), with or without ligated solvent molecules (S). The uranyl antisymmetric and symmetric stretching frequencies were measured for complexes with general formula [UO2A(S)n]+, where A was hydroxide, methoxide, or acetate; S was water, ammonia, acetone, or acetonitrile; and n = 0-3. The values for the antisymmetric stretching frequency for uranyl ligated with only an anion ([UO2A]+) were as low or lower than measurements for [UO2]2+ ligated with as many as five strong neutral donor ligands and are comparable to solution-phase values. This result was surprising because initial DFT calculations predicted values that were 30-40 cm(-1) higher, consistent with intuition but not with the data. Modification of the basis sets and use of alternative functionals improved computational accuracy for the methoxide and acetate complexes, but calculated values for the hydroxide were greater than the measurement regardless of the computational method used. Attachment of a neutral donor ligand S to [UO2A]+ produced [UO2AS]+, which produced only very modest changes to the uranyl antisymmetric stretch frequency, and did not universally shift the frequency to lower values. DFT calculations for [UO2AS]+ were in accord with trends in the data and showed that attachment of the solvent was accommodated by weakening of the U-anion bond as well as the uranyl. When uranyl frequencies were compared for [UO2AS]+ species having different solvent neutrals, values decreased with increasing neutral nucleophilicity.

32 Reads
  • Source
    • "Indium has the atomic number of forty-nine and atomic number of antimony is fifty-one. LanL2DZ basis set is good choice to optimize InSb nanostructures along with Becke's three-parameter hybrid function (B3LYP) [10] [11] [12] [13] [14]. Moreover LanL2DZ basis set can be applied to the following elements such as H, Li–La and Hf–Bi. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The realistic InSb nanostructures namely InSb nanoring, InSb nanocube, InSb nanocube-18, InSb nanosheet, InSb nanocage and InSb nanocube-27 are simulated and optimized successfully using B3LYP/LanL2DZ basis set. The stability of InSb nanostructures is studied in terms of binding energy, vibrational studies and calculated energy. The electronic properties of InSb nanostructures are discussed using ionization potential, electron affinity and HOMO–LUMO gap. Point symmetry and dipole moment of InSb nanostructures are reported. Incorporation of impurity atom in InSb nanostructures is studied using embedding energy. The present study provides the information regarding the enhanced electronic properties of InSb nanostructure which finds its potential importance in microelectronics and optoelectronic devices.
    AEJ - Alexandria Engineering Journal 06/2014; 53(2). DOI:10.1016/j.aej.2014.03.008
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: UO2+-solvent complexes having the general formula [UO2-(ROH)]+ (R=H, CH3, C2H 5, and n-C3H7) are formed using electrospray ionization and stored in a Fourier transform ion cyclotron resonance mass spectrometer, where they are isolated by mass-to-charge ratio, and then photofragmented using a free-electron laser scanning through the 10 μm region of the infrared spectrum. Asymmetric O = U = O stretching frequencies (ν3) are measured over a very small range [from ∼953 cm -1 for H2O to ∼944 cm-1 for n-propanol (n-PrOH)] for all four complexes, indicating that the nature of the alkyl group does not greatly affect the metal centre. The ν3 values generally decrease with increasing nucleophilicity of the solvent, except for the methanol (MeOH)-containing complex, which has a measured ν3 value equal to that of the n-PrOH-containing complex. The ν3 frequency values for these U(V) complexes are about 20 cm-1 lower than those measured for isoelectronic U(VI) ion-pair species containing analogous alkoxides. ν3 values for the U(V) complexes are comparable to those for the anionic [UO2(NO3)3]- complex, and 40-70 cm-1 lower than previously reported values for ligated uranyl(-VI) dication complexes. The lower frequency is attributed to weakening of the O=U=O bonds by repulsion related to reduction of the U metal centre, which increases electron density in the antibonding π* orbitals of the uranyl moiety. Computational modelling of the ν3 frequencies using the B3LYP and PBE functionals is in good agreement with the IRMPD measurements, in that the calculated values fall in a very small range and are within a few cm-1 of measurements. The values generated using the LDA functional are slightly higher and substantially overestimate the trends. Subtleties in the trend in ν3 frequencies for the H2O-MeOH-EtOH-n-PrOH series are not reproduced by the calculations, specifically for the MeOH complex, which has a lower than expected value.
    ChemPhysChem 06/2008; 9(9):1278-85. DOI:10.1002/cphc.200800034 · 3.42 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the performance of DFT in U(VI) chemistry. A large, representative selection of functionals has been tested, in combination with two ECPs developed in Stuttgart that have different-sized cores (60 and 78 electrons for U). In addition, several tests were undertaken with another 14 electron pseudopotential, which was developed in Los Alamos. The experimental database contained vibrational wavenumbers, thermochemical data, and (19)F chemical shifts for molecules of the type UF(6-n)Cl(n). For the prediction of vibrational wavenumbers, the large-core RECP (14 electrons) gives results that are at least as good as those obtained with the small-core RECP (32 electrons). GGA functionals are as successful as hybrid GGA for vibrational spectroscopy; typical errors are only a few percent with the Stuttgart pseudopotentials. For thermochemistry, hybrid versions of DFT are more successful than GGA, LDA, or meta-GGA. Marginally better results are obtained with a 32 electron ECP than with 14; since the experimental uncertainties are at least 25 kJ/mol for each reaction, the best functionals give results that are essentially indistinguishable from experiment. However, large-basis CCSD(T) results match experiment better than any DFT that we examined. Our findings for NMR spectroscopy are rather disappointing; no combination of pseudopotential, functional, and basis yields even a qualitatively correct prediction of trends in the (19)F chemical shifts of UF(6-n)Cl(n) species. Results yielded by the large-core RECP are, in general, slightly less bad than those obtained with the small core. We conclude that DFT cannot be recommended for predictions of NMR spectra in this series of compounds, though this conclusion should not be generalized. Our most important result concerns the good performance of the large-core Stuttgart pseudopotential. Given its computational efficiency, we recommend that it be used with DFT methods for the prediction of molecular geometries, vibrational frequencies, and thermochemistry of a given oxidation state. The hybrid GGA functionals MPW1PW91 and PBE0 give the best results overall.
    The Journal of Physical Chemistry A 08/2008; 112(33):7632-42. DOI:10.1021/jp801124u · 2.69 Impact Factor
Show more