D. K. Shuh

Argonne National Laboratory, Lemont, Illinois, United States

Are you D. K. Shuh?

Claim your profile

Publications (294)683.24 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Covalency in Ln-Cl bonds of Oh-LnCl6(x-) (x = 3 for Ln = Ce(III), Nd(III), Sm(III), Eu(III), Gd(III); x = 2 for Ln = Ce(IV)) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L3,2-edge and M5,4-edge XAS were also used to characterize CeCl6(x-) (x = 2, 3). The M5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce(III) and Ce(IV)). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (t2g* and eg*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce(III) to Ce(IV) had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl6(3-) (formally Ln(III)), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce(IV) 4f-orbital mixing (t1u* + t2u*) in CeCl6(2-). This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl6(2-) (M = Ti, Zr, Hf, U).
    Journal of the American Chemical Society 02/2015; DOI:10.1021/ja510067v · 11.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Reaction of the neutral diniobium benzene complex {[Nb(BDI)NtBu]2(μ-C6H6)} (BDI = N,N′-diisopropylbenzene-β-diketiminate) with Ag[B(C6F5)4] results in a single electron oxidation to produce a cationic diniobium arene complex, {[Nb(BDI)NtBu]2(μ-C6H6)}{B(C6F5)4}. Investigation of the solid state and solution phase structure using single-crystal X-ray diffraction, cyclic voltammetry, magnetic susceptibility, and multinuclear NMR spectroscopy indicates that the oxidation results in an asymmetric molecule with two chemically inequivalent Nb atoms. Further characterization using density functional theory (DFT) calculations, UV-visible, Nb L3,2-edge X-ray absorption near-edge structure (XANES), and EPR spectroscopies supports assignment of a diniobium complex, in which one Nb atom carries a single unpaired electron that is not largely delocalized on the second Nb atom. During the oxidative transformation, one electron is removed from the δ-bonding HOMO, which causes a destabilization of the molecule and formation of an asymmetric product. Subsequent reactivity studies indicate that the oxidized product allows access to metal-based chemistry with substrates that did not exhibit reactivity with the starting neutral complex.
    Chemical Science 11/2014; 6(2). DOI:10.1039/C4SC02705A · 8.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 3,4,3-LI(1,2-HOPO), 1,5,10,14-tetra(1-hydroxy-2-pyridon-6-oyl)-1,5,10,14-tetraazatetradecane), is a potent octadentate chelator of actinides. It is being developed as a decorporation treatment for internal contamination with radionuclides. Conventional HPLC methods exhibited speciation peaks and bridging, likely attributable to the agent's complexation with residual metallic ions in the HPLC system. Derivatization of the target ligand in situ with Fe(III) chloride, however, provided a single homogeneous iron-complex that can readily be detected and analyzed by HPLC. The HPLC method used an Agilent Eclipse XDB-C18 column (150mm×4.6mm, 5μm) at 25°C with UV detection at 280nm. A gradient elution, with acetonitrile (11% to 100%)/buffer mobile phase, was developed for impurity profiling. The buffer consisted of 0.02% formic acid and 10mM ammonium formate at pH 4.6. An Agilent 1200 LC-6530 Q-TOF/MS system was employed to characterize the [Fe(III)-3,4,3-LI(1,2-HOPO)] derivative and impurities. The proposed HPLC method was validated for specificity, linearity (concentration range 0.13-0.35mg/mL, r=0.9999), accuracy (recovery 98.3-103.3%), precision (RSD≤1.6%) and sensitivity (LOD 0.08μg/mL). The LC/HRMS revealed that the derivative was a complex consisting of one 3,4,3-LI(1,2-HOPO) molecule, one hydroxide ligand, and two iron atoms. Impurities were also identified with LC/HRMS. The validated HPLC method was used in shelf-life evaluation studies which showed that the API remained unchanged for one year at 25°C/60% RH. Copyright © 2014 Elsevier B.V. All rights reserved.
    Journal of Pharmaceutical and Biomedical Analysis 10/2014; 102C:443-449. DOI:10.1016/j.jpba.2014.10.015 · 2.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the electronic structure of three newly synthesized nitrogen-donor uranyl complexes [(UO2)(H2bbp)Cl2], [(UO)2(Hbbp)(Py)Cl], and [(UO2)(bbp)(Py)2] using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy experiments and simulations. The complexes studied feature derivatives of the tunable tridentate N-donor ligand 2,6-bis(2-benzimidazyl)pyridine (bbp) and exhibit discrete chemical differences in uranyl coordination. The sensitivity of the N K-edge X-ray absorption spectrum to local bonding and charge transfer is exploited to systematically investigate the evolution of structural as well as electronic properties across the three complexes. A thorough interpretation of the measured experimental spectra is achieved via ab initio NEXAFS simulations based on the eXcited electron and Core-Hole (XCH) approach and enables the assignment of spectral features to electronic transitions on specific absorbing sites. We find that ligand-uranyl bonding leads to a signature blue shift in the N K-edge absorption onset, resulting from charge displacement toward the uranyl, while changes in the equatorial coordination shell of the uranyl lead to more subtle modulations in the spectral features. Theoretical simulations show that the flexible local chemistry at the nonbinding imidazole-N sites of the bbp ligand is also reflected in the NEXAFS spectra and highlights potential synthesis strategies to improve selectivity. In particular, we find that interactions of the bbp ligand with solvent molecules can lead to changes in ligand-uranyl binding geometry while also modulating the K-edge absorption. Our results suggest that NEXAFS spectroscopy combined with first-principles interpretation can offer insights into the coordination chemistry of analogous functionalized conjugated ligands.
    Inorganic Chemistry 10/2014; 53(21). DOI:10.1021/ic501107a · 4.79 Impact Factor
  • Source
    Plutonium Futures – The Science 2014, Las Vegas, NV, USA; 09/2014
  • Guoxin Tian, David K Shuh
    [Show abstract] [Hide abstract]
    ABSTRACT: The complexation of americium(iii) with nitrate was studied at temperatures from 10 to 85 °C in 1 M HNO3-HClO4 by spectrophotometry. The 1 : 1 complex species, AmNO3(2+), was identified and the stability constants were calculated from the absorption spectra recorded for titrations at several temperatures. Specific ion interaction theory (SIT) was used for ionic strength corrections to obtain the stability constants of AmNO3(2+) at infinite dilution and variable temperatures. The absorption spectra of Am(iii) in diluted HClO4 were also reviewed, and the molar absorptivity of Am(iii) at around 503 nm and 813 nm was re-calibrated by titrations with standardized DTPA solutions to determine the concentration of Am(iii).
    Dalton Transactions 07/2014; 43(39). DOI:10.1039/c4dt01183j · 4.10 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The solid-state MU8Q17 compounds ScU8S17, CoU8S17, NiU8S17, TiU8Se17, VU8Se17, CrU8Se17, CoU8Se17, and NiU8Se17 were synthesized from the reactions of the elements at 1173 or 1123 K. These isostructural compounds crystallize in space group C2h3 - C2/m of the monoclinic system in the CrU8S17 structure type. X-ray absorption near-edge structure spectroscopic studies of ScU8S17 indicate that it contains Sc3+, and hence charge balance is achieved with a composition that includes U3+ as well as U4+. The other compounds charge balance with M2+ and U4+. Magnetic susceptibility measurements on ScU8S17 indicate antiferromagnetic couplings and a highly reduced effective magnetic moment. Ab Initio calculations find the compound to be metallic. Surprisingly, the Sc–S distances are actually longer than all the other M–S interactions, even though the ionic radii of Sc3+, low-spin Cr2+, and Ni2+ are similar.
    ChemInform 06/2014; 53(13). DOI:10.1021/ic500721d
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Understanding the uranium 5f/6d orbital mixing with oxygen 2p valence orbitals in uranium oxides is important for advancing nuclear technology. Unfortunately, U–O orbital mixing is difficult to probe experimentally. In this manuscript, U–O bonding is evaluated in U3O8 using O K-edge X-ray absorption spectroscopy (XAS). To confirm that the O K-edge XAS spectra were correct and did not contain contributions from surface contamination, three different sample types were investigated using three unique detection methods. Specifically an epitaxial film of U3O8 deposited on Al2O3 (PAD-U3O8) was probed using grazing-incidence fluorescence yield (GIFY) detection, a bulk powder of α-phase U3O8 was analyzed with fluorescence yield (FY) detection at normal incidence, and particles of α-phase U3O8 were studied in transmission mode using a scanning transmission X-ray microscope (STXM). Experimental spectra have been presented in the context of previously published computational results from DFT using the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional. Overall, the comparative analyses of PAD-U3O8 and α-phase U3O8 samples enabled identification of unique signatures associated with oxygen 2p orbital mixing with both UV and UVI 5f and 6d valence orbitals.
    Journal of Electron Spectroscopy and Related Phenomena 06/2014; 194. DOI:10.1016/j.elspec.2014.03.005 · 1.55 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Two isostructural series of trigonal prismatic complexes, M(Bp(Me))3 and M(Bc(Me))3 (M = Y, Tb, Dy, Ho, Er, U; [Bp(Me)](-) = dihydrobis(methypyrazolyl)borate; [Bc(Me)](-) = dihydrobis(methylimidazolyl)borate) are synthesized and fully characterized to examine the influence of ligand donor strength on slow magnetic relaxation. Investigation of the dynamic magnetic properties reveals that the oblate electron density distributions of the Tb(3+), Dy(3+), and U(3+) metal ions within the axial ligand field leads to slow relaxation upon application of a small dc magnetic field. Significantly, the magnetization relaxation is orders of magnitude slower for the N-heterocyclic carbene complexes, M(Bc(Me))3, than for the isomeric pyrazolate complexes, M(Bp(Me))3. Further, investigation of magnetically dilute samples containing 11-14 mol% of Tb(3+), Dy(3+), or U(3+) within the corresponding Y(3+) complex matrix reveals thermally-activated relaxation is favored for the M(Bc(Me))3 complexes, even when dipolar interactions are largely absent. Notably, the dilute species U(Bc(Me))3 exhibits Ueff ~33 cm(-1), representing the highest barrier yet observed for a U(3+) molecule demonstrating slow relaxation. Additional analysis through lanthanide XANES, X-band EPR, and (1)H NMR spectroscopies provides evidence that the origin of the slower relaxation derives from the greater magnetic anisotropy enforced within the strongly donating N-heterocyclic carbene coordination sphere. These results show that, like molecular symmetry, ligand donating ability is a variable that can be controlled to the advantage of the synthetic chemist in the design of single-molecule magnets with enhanced relaxation barriers.
    Journal of the American Chemical Society 03/2014; 136(16). DOI:10.1021/ja501569t · 11.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The reaction of UO2Cl2·3THF with the tridentate nitrogen donor ligand 2,6-bis(2-benzimidazolyl)pyridine (H2BBP) in pyridine leads to the formation of three different complexes: [(UO2)(H2BBP)Cl2] (1), [(UO)2(HBBP)(Py)Cl] (2), and [(UO2)(BBP)(Py)2] (3) after successive deprotonation of H2BBP with a strong base. Crystallographic determination of 1-3 reveals that increased charge through ligand deprotonation and displacement of chloride leads to equatorial planarity about uranyl as well as a more compact overall coordination geometry. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectra of 1-3 at the U-4d edges have been recorded using a soft X-ray Scanning Transmission X-ray Microscope (STXM) and reveal the uranium 4d5/2 and 4d3/2 transitions at energies associated with uranium in the hexavalent oxidation state. First-principles Density Functional Theory (DFT) electronic structure calculations for the complexes have been performed to determine and validate the coordination characteristics, which correspond well to the experimental results.
    Inorganic Chemistry 02/2014; 53(5). DOI:10.1021/ic4026359 · 4.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Evidence for metal-carbon orbital mixing in thorocene and uranocene was determined from DFT calculations and carbon K-edge X-ray absorption spectra (XAS) collected with a scanning transmission X-ray microscope (STXM). Both the experimental and computational results showed that the 5f orbitals engaged in significant δ-type mixing with the C8H82− ligands, which increased as the 5f orbitals dropped in energy on moving from Th4+ to U4+. The first experimental evidence for extensive ϕ-orbital interactions has been provided by the C K-edge XAS analysis of thorocene; however, ϕ-type covalency in uranocene was negligible. The results highlighted two contrasting trends in orbital mixing from one pair of highly symmetric molecules, and showed that covalency does not increase uniformly for different molecular orbital interactions with later actinides.
    Chemical Science 01/2014; 5(1):351. DOI:10.1039/c3sc52030g · 8.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The study addresses the possibilities of immobilizing the mobile species of actinides in the geosphere using metallic iron. Sorption on corroding iron is well known, but there have been uncertainties as to the possibilities of reducing the actinyl species to sparingly soluble oxides and, thereby, permanently immobilizing them. Resonant inelastic x-ray scattering (RIXS) measurements at the actinide 5d edges on Fe foils exposed to U(VI) and Np(V) solutions in ground water unambigiously indicate reduction of actinides to respectively U(IV) and Np(IV) on iron surfaces. The reduction manifests itself in an appearance of distinct specific signatures of U(IV) and Np(IV) in the RIXS profile of 5f-5f excitations. Such signatures and RIXS intensity/cross-section behaviour with varying energy of incident photons can be reproduced by model atomic-multiplet calculations of the RIXS spectra. By normalizing the RIXS signal of corresponding 5f-5f excitations to core-to-core 6p-to-5d characteristic fluorescence transitions of actinides, their reduction rates on Fe samples with different exposure to actinide solutions can be estimated. Observed reduction implies similar processes in the nuclear waste canister thus suggesting reduced probability of nuclear waste release with ground waters from the canister.
    Analytical Chemistry 11/2013; 85(23). DOI:10.1021/ac4020534 · 5.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Forty-three atomic emission lines for 235U and 238U were compiled for computer simulation of isotopic analysis using laser induced breakdown spectroscopy (LIBS). The spectral line profile was assumed to be Lorentzian in shape and the magnitude of three common types of noises (detector-read, photon-shot and flicker) were experimentally determined and incorporated into the simulation. Precision and root mean square error of prediction (RMSEP) for isotopic analysis of a single U line were simulated, and it was found that analytical performance (precision) primarily depended on the signal-to-background ratio (SBR) and net intensity of the emission line, rather than on the magnitude of isotopic splitting (IS), when partial least squares (PLS) was used for calibration. This is because PLS multivariate calibration can be performed correctly even when the spectra are only partially resolved, which in turn relaxes the requirement on having IS larger than the spectral resolution. The analytical performance was found to improve with multiple-line analysis. Depending on the criteria (e.g., SBR, net intensity, magnitude of IS, or best single-line performance) used in sorting the spectral lines into the multiline pool, improvement factors ranging from 2 × to 9 × were obtained. The absolute uncertainty of isotopic analysis is practically constant and independent of isotopic abundance, which makes experimental estimation of the detection limit in isotopic analysis straightforward because one can experimentally measure this uncertainty with one arbitrary and conveniently chosen isotopic standard and then estimate the detection limit through simple extrapolation.
    Spectrochimica Acta Part B Atomic Spectroscopy 11/2013; 89:40–49. DOI:10.1016/j.sab.2013.09.001 · 3.15 Impact Factor
  • Source
    Article: Page 1 of 2
    [Show abstract] [Hide abstract]
    ABSTRACT: chromatographic separation and 249 Bk/ 248 Cm and 249 Cf/ 248 Cm elemental ratios determination by inductively coupled plasma quadrupole mass spectrometry. Talanta, Vol. 106, p. 39, 2013. 243 Am neutron-induced fission cross section in the fast neutron energy range. Phys. Rev. C.. Accurate determination of Curium and Californium isotopic ratios by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) in 248 Cm samples for transmutation studies.
    Talanta 10/2013; 291(106). · 3.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Metal-carbon covalence in (C5H5)2MCl2 (M = Ti, Zr, Hf) has been evaluated using carbon K-edge X-ray absorption spectroscopy (XAS) as well as ground-state and time-dependent hybrid density functional theory (DFT and TDDFT). Differences in orbital mixing were determined experimentally using transmission XAS of thin crystalline material with a scanning transmission X-ray microscope (STXM). Moving down the periodic table (Ti to Hf) has a marked effect on the experimental transition intensities associated with the low-lying antibonding 1a1* and 1b2* orbitals. The peak intensities, which are directly related to the M-(C5H5) orbital mixing coefficients, increase from 0.08(1) and 0.26(3) for (C5H5)2TiCl2 to 0.31(3) and 0.75(8) for (C5H5)2ZrCl2, and finally to 0.54(5) and 0.83(8) for (C5H5)2HfCl2. The experimental trend toward increased peak intensity for transitions associated with 1a1* and 1b2* orbitals agrees with the calculated TDDFT oscillator strengths [0.10 and 0.21, (C5H5)2TiCl2; 0.21 and 0.73, (C5H5)2ZrCl2; 0.35 and 0.69, (C5H5)2HfCl2] and with the amount of C 2p character obtained from the Mulliken populations for the antibonding 1a1* and 1b2* orbitals [8.2 and 23.4%, (C5H5)2TiCl2; 15.3 and 39.7%, (C5H5)2ZrCl2; 20.1 and 50.9%, (C5H5)2HfCl2]. The excellent agreement between experiment, theory, and recent Cl K-edge XAS and DFT measurements shows that C 2p orbital mixing is enhanced for the diffuse Hf (5d) and Zr (4d) atomic orbitals in relation to the more localized Ti (3d) orbitals. These results provide insight into how changes in M-Cl orbital mixing within the metallocene wedge are correlated with periodic trends in covalent bonding between the metal and the cyclopentadienide ancillary ligands.
    Journal of the American Chemical Society 09/2013; 135(39). DOI:10.1021/ja405844j · 11.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Syntheses of neutral halide and aryl vanadium bisimides are described. Treatment of VCl2(NtBu)[NTMS(N(t)Bu)], 2, with PMe3, PEt3, PMe2Ph, or pyridine gave vanadium bisimides via TMSCl elimination in good yield: VCl(PMe3)2(N(t)Bu)2 3, VCl(PEt3)2(N(t)Bu)2 4, VCl(PMe2Ph)2(N(t)Bu)2 5, and VCl(Py)2(N(t)Bu)2 6. The halide series (Cl-I) was synthesized by use of TMSBr and TMSI to give VBr(PMe3)2(N(t)Bu)2 7 and VI(PMe3)2(N(t)Bu)2 8. The phenyl derivative was obtained by reaction of 3 with MgPh2 to give VPh(PMe3)2(N(t)Bu)2 9. These neutral complexes are compared to the previously reported cationic bisimides [V(PMe3)3(N(t)Bu)2][Al(PFTB)4] 10, [V(PEt3)2(N(t)Bu)2][Al(PFTB)4] 11, and [V(DMAP)(PEt3)2(N(t)Bu)2][Al(PFTB)4] 12 (DMAP = dimethylaminopyridine, PFTB = perfluoro-tert-butoxide). Characterization of the complexes by X-ray diffraction, (13)C NMR, (51)V NMR, and V L3,2-edge X-ray absorption near-edge structure (XANES) spectroscopy provides a description of the electronic structure in comparison to group 6 bisimides and the bent metallocene analogues. The electronic structure is dominated by π bonding to the imides, and localization of electron density at the nitrogen atoms of the imides is dictated by the cone angle and donating ability of the axial neutral supporting ligands. This phenomenon is clearly seen in the sensitivity of (51)V NMR shift, (13)C NMR Δδαβ, and L3-edge energy to the nature of the supporting phosphine ligand, which defines the parameters for designing cationic group 5 bisimides that would be capable of breaking stronger σ bonds. Conversely, all three methods show little dependence on the variable equatorial halide ligand. Furthermore, this analysis allows for quantification of the electronic differences between vanadium bisimides and the structurally analogous mixed Cp/imide system CpV(N(t)Bu)X2 (Cp = C5H5(1-)).
    Inorganic Chemistry 09/2013; 52(19). DOI:10.1021/ic4020543 · 4.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Although transition metal cyano bimetallic compounds have been well known for decades for their interesting optical and magnetic properties, reports on actinide hexacyanoferrate compounds are scarce. For instance, a thorough structural description is still lacking. Another question is the possible covalency or charge transfer effects in these materials that are known to foster electron delocalization with a large variety of transition metal cations. In this paper, new members of the actinide(IV) hexacyanoferrates have been synthesized with Th, Np and Pu. This is the first review of thorium to plutonium hexacyanoferrate compounds since the early investigations during the Manhattan Project some 70 years ago. We have carried out an extensive structural characterization using powder X-ray Diffraction (XRD), X-ray Absorption Spectroscopy (XAS) and X-ray microscopy for the plutonium adduct. The crystallographic space group of microcrystalline Th, Np and Pu hexacyanoferrate compounds appears to be very similar to that of the early lanthanide adducts, suggesting that the tetravalent actinides are arranged in a tricapped trigonal prismatic polyhedron of coordination number 9, in which the actinide atom is bonded to six nitrogen atoms and to three water molecules. Further combined analysis of the iron K-edge and actinide LIII-edge EXAFS data and XRD data provided the basis for a three-dimensional molecular model. Structural data in terms of actinide–ligand bond lengths have been compared to those reported for the parent lanthanide(III) compounds, confirming the structural similarities. In addition, two new structures with the thorium cation have been obtained and described using single-crystal XRD: (H5O2)[Th(DMF)5(H2O)]2[Fe(CN)6]3 and [Th(DMF)4(H2O)3][Fe(CN)6](NO3)·2H2O. This structural description of the Th, Np and Pu hexacyanoferrate system will be followed by a semi-quantitative electronic description of the actinide–cyano bond using NEXAFS data analysis in a coming paper.
    New Journal of Chemistry 06/2013; 37(10):-. DOI:10.1039/C3NJ00318C · 3.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The synthesis and study of soft-donor uranyl complexes can provide new insights into the coordination chemistry of non-aqueous [UO]2^+ Recently, the tunable N-donor ligand 2,6-Bis(2-benzimidazyl)pyridine (BBP) was employed to produce novel uranyl complexes in which the [UO]2^+ cation is ligated by anionic and covalent groups with discrete chemical differences. In this work we investigate the electronic structure of the three such uranyl-BBP complexes via near-edge X-ray absorption fine structure (NEXAFS) experiments and simulations using the eXcited electron and Core-Hole (XCH) approach [1]. The evolution of the structural as well as electronic properties across the three complexes is studied systematically. Computed N K-edge and O K-edge NEXAFS spectra are compared with experiment and spectral features assigned to specific electronic transitions in these complexes. Studying the variations in spectral features arising from N K-edge absorption provides a clear picture of ligand-uranyl bonding in these systems. References: [1] D. Prendergast and G. Galli, X-ray absorption spectra of water from first-principles calculations, Phys. Rev. Lett., 215502 (2006).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Advancing theories of how metal-oxygen bonding influences metal oxo properties can expose new avenues for innovation in materials science, catalysis, and biochemistry. Historically, spectroscopic analyses of the transition metal MO(4)(x-) anions have formed the basis for new M-O bonding theories. Herein, relative changes in M-O orbital mixing in MO(4)(2-) (M = Cr, Mo, W) and MO(4)(-) (M = Mn, Tc, Re) are evaluated for the first time by nonresonant inelastic X-ray scattering, X-ray absorption spectroscopy using fluorescence and transmission (via a scanning transmission X-ray microscope), and time-dependent density functional theory. The results suggest that moving from Group 6 to Group 7 or down the triads increases M-O e* (π*) mixing; for example, it more than doubles in ReO(4)(-) relative to CrO(4)(2-). Mixing in the t(2)* orbitals (σ* + π*) remains relatively constant within the same Group, but increases on moving from Group 6 to Group 7. These unexpected changes in orbital energy and composition for formally isoelectronic tetraoxometalates are evaluated in terms of periodic trends in d orbital energy and radial extension.
    Journal of the American Chemical Society 01/2013; 135(5). DOI:10.1021/ja310223b · 11.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Monometallic niobium arene complexes [Nb(BDI)(NtBu)(R-C6H5)] (2a: R = H and 2b: R = Me, BDI = N,N'-diisopropylbenzene-β-diketiminate) were synthesized and were found to slowly converted into the diniobium inverted arene sandwich complexes [[(BDI)Nb(NtBu)]2(μ-RC6H5)] (7a: R = H and 7b: R = Me) in solution. The kinetics of this reaction were followed by 1H NMR spectroscopy, and is in agreement with a dissociative mechanism. Compounds 7a-b showed a lack of reactivity towards small molecules - even at elevated temperatures - which is unusual in the chemistry of inverted sandwich complexes. However, protonation of the BDI ligands occurred readily on treatment with [H(OEt2)][B(C6F5)4], resulting in the mono-protonated cationic inverted sandwich complex 8 [[(BDI#)Nb(NtBu)][(BDI)Nb(NtBu)](μ-C6H5)][B(C6F5)4] and the dicationic complex 9 [[(BDI#)Nb(NtBu)]2(μ-RC6H5)][B(C6F5)4]2 (BDI# = (ArNC(Me))2CH2). NMR, UV-vis and X-ray absorption near-edge structure (XANES) spectroscopies were used to characterize this unique series of diamagnetic molecules as a means of determining how best to describe the Nb-arene interactions. The X-ray crystal structures, UV-visible spectra, arene 1H NMR chemical shifts and large JCH coupling con-stants provide evidence for donation of electron density from the Nb d-orbitals into the antibonding π system of the arene ligands. However, Nb L3/2-edge XANES spectra and the lack of sp3 hybridization of the arene carbon indicate that the Nb→arene donation is not accompanied by an increase in formal oxidation state, and suggest that 4d2 electronic configurations are appropriate to describe the Nb atoms in all four complexes.
    Journal of the American Chemical Society 01/2013; 135(8). DOI:10.1021/ja311966h · 11.44 Impact Factor

Publication Stats

4k Citations
683.24 Total Impact Points


  • 2014
    • Argonne National Laboratory
      Lemont, Illinois, United States
  • 2011–2014
    • Northwest University
      Evanston, Illinois, United States
  • 1992–2014
    • Lawrence Berkeley National Laboratory
      • • Chemical Sciences Division
      • • Materials Sciences Division
      Berkeley, California, United States
  • 1993–2013
    • University of California, Berkeley
      • • Department of Chemistry
      • • Lawrence Berkeley Laboratory
      • • Department of Physics
      Berkeley, California, United States
  • 2010
    • Northwestern University
      • Department of Chemistry
      Evanston, Illinois, United States
  • 1987–2010
    • University of California, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Angeles, California, United States
  • 1992–2007
    • CSU Mentor
      Long Beach, California, United States
  • 2000
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
  • 1996
    • Tulane University
      New Orleans, Louisiana, United States
  • 1993–1996
    • University of California, Riverside
      Riverside, California, United States
  • 1995
    • Rutgers, The State University of New Jersey
      • Department of Physics
      Нью-Брансуик, New Jersey, United States