A5034686235- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Radioactive element chemistry and processing
- Crystallography and molecular interactions
- Nuclear Materials and Properties
- Lanthanide and Transition Metal Complexes
- Organometallic Complex Synthesis and Catalysis
- Inorganic Chemistry and Materials
- Rare-earth and actinide compounds
- Chemical Synthesis and Characterization
- Advanced Chemical Physics Studies
- X-ray Spectroscopy and Fluorescence Analysis
- Coordination Chemistry and Organometallics
- Organometallic Compounds Synthesis and Characterization
- Forensic Fingerprint Detection Methods
- Crystal Structures and Properties
- Metal Extraction and Bioleaching
- Nuclear materials and radiation effects
- Machine Learning in Materials Science
- High-pressure geophysics and materials
- Coal and Its By-products
- Organic and Molecular Conductors Research
- Mesoporous Materials and Catalysis
- Radioactive contamination and transfer
- Metal complexes synthesis and properties
Los Alamos National Laboratory
2010-2022
Environmental Molecular Sciences Laboratory
2009-2010
Pacific Northwest National Laboratory
2009-2010
Lawrence Berkeley National Laboratory
2010
Covalency in Ln–Cl bonds of Oh-LnCl6x– (x = 3 for Ln CeIII, NdIII, SmIII, EuIII, GdIII; x 2 CeIV) 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 M5,4-edge XAS were also used to characterize CeCl6x– 2, 3). The spectra modeled configuration interaction calculations. results evaluated as a function (1) the lanthanide (Ln) metal identity, which was varied across series from...
Chlorine K-edge X-ray absorption spectroscopy (XAS) and ground-state time-dependent hybrid density functional theory (DFT) were used to probe the electronic structures of O(h)-MCl(6)(2-) (M = Ti, Zr, Hf, U) C(4v)-UOCl(5)(-), determine relative contributions valence 3d, 4d, 5d, 6d, 5f orbitals in M-Cl bonding. Spectral interpretations guided by DFT calculated transition energies oscillator strengths, which agree well with experimental XAS spectra. The data provide new spectroscopic evidence...
We describe the use of Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state time-dependent hybrid density functional theory (DFT) to probe electronic structure determine degree orbital mixing in M−Cl bonds for (C5Me5)2MCl2 (M = Ti, 1; Zr, 2; Hf, 3; Th, 4; U, 5), where we can directly compare a class structurally similar compounds d- f-elements. Pre-edge features XAS data group IV transition-metals 1−3 provide direct evidence covalent mixing. The amount 3p character was...
Evaluating the nature of chemical bonding for actinide elements represents one most important and long-standing problems in science. We directly address this challenge contribute a Cl K-edge X-ray absorption spectroscopy relativistic density functional theory study that quantitatively evaluates An–Cl covalency AnCl62– (AnIV = Th, U, Np, Pu). The results showed significant mixing between 3p- AnIV 5f- 6d-orbitals (t1u*/t2u* t2g*/eg*), with showing more pronounced covalent than 5f-orbitals....
Evidence for metal–carbon orbital mixing in thorocene and uranocene was determined from DFT calculations carbon K-edge X-ray absorption spectra (XAS) collected with a scanning transmission microscope (STXM). Both the experimental computational results showed that 5f orbitals engaged significant δ-type C8H82− ligands, which increased as dropped energy on moving Th4+ to U4+. The first evidence extensive ϕ-orbital interactions has been provided by C XAS analysis of thorocene; however, ϕ-type...
Uranium compounds supported by redox-active α-diimine ligands, which have methyl groups on the ligand backbone and bulky mesityl substituents nitrogen atoms {MesDABMe = [ArN═C(Me)C(Me)═NAr], where Ar 2,4,6-trimethylphenyl (Mes)}, are reported. The addition of 2 equiv MesDABMe, 3 KC8, 1 UI3(THF)4 produced bis(ligand) species (MesDABMe)2U(THF) (1). metallocene derivative, Cp2U(MesDABMe) (2), was generated an equimolar ratio MesDABMe KC8 to Cp3U. bond lengths in molecular structure both confirm...
Synthetic routes to salts containing uranium bis-imido tetrahalide anions [U(NR)(2)X(4)](2-) (X = Cl(-), Br(-)) and non-coordinating NEt(4)(+) PPh(4)(+) countercations are reported. In general, these compounds can be prepared from U(NR)(2)I(2)(THF)(x) (x 2 R (t)Bu, Ph; x 3 Me) upon addition of excess halide. providing stable coordination complexes with the [U(NMe)(2)](2+) cation also reacts Br(-) form [NEt(4)](2)[U(NMe)(2)Br(4)] complexes. These materials were used as a platform compare...
The dithiophosphinic acid HS(2)P(o-CF(3)C(6)H(4))(2) is known to exhibit exceptionally high extraction selectivities for trivalent minor actinides (Am and Cm) in the presence of lanthanides. To generate insight that may account this observation, a series [PPh(4)][S(2)PR(2)] complexes, where R = Me (1), Ph (2), p-CF(3)C(6)H(4) (3), m-CF(3)C(6)H(4) (4), o-CF(3)C(6)H(4) (5), o-MeC(6)H(4) (6), o-MeOC(6)H(4) (7), have been investigated using sulfur K-edge X-ray absorption spectroscopy (XAS)...
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 the transition MO4x– anions have formed basis M–O theories. Herein, relative changes orbital mixing MO42– (M = Cr, Mo, W) MO4– Mn, Tc, Re) are evaluated first time by nonresonant inelastic X-ray scattering, absorption spectroscopy using fluorescence transmission (via a scanning microscope),...
High-purity syntheses are reported for a series of first, second, and third row transition metal actinide hexahalide compounds with equivalent, noncoordinating countercations: (Ph(4)P)(2)TiF(6) (1) (Ph(4)P)(2)MCl(6) (M = Ti, Zr, Hf, Th, U, Np, Pu; 2-8). While reaction between MCl(4) U) 2 equiv Ph(4)PCl provided 3, 4, 6, 1, 2, 5, 7, 8 required multistep procedures. For example, cation exchange (NH(4))(2)TiF(6) produced which was used in subsequent anion Me(3)SiCl to synthesize 2. 8, synthetic...
Metal-carbon covalence in (C5H5)2MCl2 (M = Ti, Zr, Hf) has been evaluated using carbon K-edge X-ray absorption spectroscopy (XAS) as well ground-state and time-dependent hybrid density functional theory (DFT TDDFT). Differences orbital mixing were determined experimentally transmission XAS of thin crystalline material with a scanning microscope (STXM). Moving down the periodic table (Ti to marked effect on experimental transition intensities associated low-lying antibonding 1a1* 1b2*...
X-ray pair distribution function (pdf) and U L3 extended x-ray absorption fine structure (EXAFS) neutron pdf measurements that give identical results for UO2 show U(VI)-oxo moieties with x rays mixed valence U4O9 U3O7, in contrast to the data indicate only U(V) sites no short U-O bonds as well other differences. In addition, although EXAFS spectra of are essentially at 30, 100, 200 K, those UO2+x compounds exhibit different nearest-neighbor distributions each temperature. Further tunneling...
Chemical signatures correlated with uranium oxide processing are of interest to forensic science for inferring sample provenance. Identification temporal changes in chemical structures process materials as a function controlled temperatures and relative humidities may provide additional information regarding history. In this study, high-purity α-U3O8 three other samples synthesized from reaction routes used nuclear conversion processes were stored under conditions over 2-3.5 years, powder...
For 3−5d transition-metal ions, the (C5R5)2MCl2 (R = H, Me for M Ti, Zr, Hf) bent metallocenes represent a series of compounds that have been central in development organometallic chemistry and homogeneous catalysis. Here, we evaluate how changes principal quantum number group IV (C5H5)2MCl2 (M Hf; 1−3, respectively) complexes affects covalency M−Cl bonds through application Cl K-edge X-ray Absorption Spectroscopy (XAS). Spectra were recorded on solid samples dispersed as thin film...
We report nonresonant inelastic x-ray scattering from the semi-core 5d levels of several actinide compounds. Dipole-forbidden, high-multipole features form a rich bound-state spectrum dependent on valence electron configuration and spin-orbit Coulomb interactions. Cross-material comparisons, together with anomalously high screening required for agreement between atomic multiplet theory experiment, demonstrate sensitivity to neighboring electronic environment, such as is needed address...
Accurate X-ray absorption spectra (XAS) of first row atoms, e.g., O, are notoriously difficult to obtain due the extreme sensitivity measurement surface contamination, self-absorption, and saturation affects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data ReO(4)(1-) provide methodology obtaining trustworthy quantitative on nonconducting molecular systems, even in presence contamination. This involves comparing measured by nonresonant inelastic...
Synthetic routes to alkyl and aryl substituted dithiophosphinate salts that contain non-coordinating PPh(4)(+) counter cations are reported. In general, these compounds can be prepared via a multi-step procedure starts with reacting secondary phosphines, i.e. HPR(2), two equivalents of elemental S. The synthetic transformation proceeds by oxidation the phosphine followed insertion S into H-P bond. This approach was used synthesize series dithiophosphinic acids were fully characterized,...
Herein, we have evaluated relative changes in M–S electronic structure and orbital mixing Group 6 MS42− dianions using solid- solution-phase S K-edge X-ray absorption spectroscopy (XAS; M = Mo, W), as well density functional theory (DFT; Cr, W) time-dependent (TDDFT) calculations. To facilitate comparison with solution measurements (conducted acetonitrile), theoretical models included gas-phase calculations those that incorporated an acetonitrile dielectric, the latter of which provided...
A new tetrathiafulvalene-salphen uranyl complex has been prepared. The system was designed to study the electronic coupling between actinides and a redox active ligand framework. Theoretical experimental methods – including DFT calculations, single crystal X-ray analysis, cyclic voltammetry, NMR IR spectroscopies were used characterize this complex.
A method to evaluate the electronic structure of minor actinide extractants is described. series compounds containing effective and ineffective (dithiophosphinates, S(2)PR(2)(-)) bound a common transition metal ion (Ni(2+)) was analyzed by structural, spectroscopic, theoretical methods. By using single that provides structurally similar compounds, contributions bonding are essentially held constant so subtle variations associated with extracting ligand can be probed UV-vis spectroscopy....
We report the interaction between B-type tri-lacunary heteropolyoxotungstate anions and actinyl(V) cations in aqueous solution, yielding a greater understanding of stability OAnO1+ linear dioxo actinide moiety. Previously we reported that B-α-[BiW9O33]9− B-α-[SbW9O33]9− will react with NpO21+ to yield [(Np3W4O15)(H2O)3(MW9O33)3]18− (M = Bi, or Sb). Single crystal structural characterisation salts these complexes revealed core which three NpV atoms interact central WVI atom through bridging...