Roy Copping

University of California, Berkeley, Berkeley, California, United States

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Publications (26)93.42 Total impact

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    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 · 4.76 Impact Factor
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    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 · 4.76 Impact Factor
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    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).
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    ABSTRACT: Around the world large quantities of sludge wastes derived from nuclear energy production are currently kept in storage facilities. In the UK, the British government has marked sludge removal as a top priority as these facilities are nearing the end of their operational lifetimes. Therefore chemical understanding of uranium uptake in Mg-rich sludge is critical for successful remediation strategies. Previous studies have explored uranium uptake by the calcium carbonate minerals, calcite and aragonite, under conditions applicable to both natural and anthropogenically perturbed systems. However, studies of the uptake by Mg-rich minerals such as brucite [Mg(OH)2], nesquehonite [MgCO3·3H2O] and hydromagnesite [Mg5(CO3)4 (OH)2·4H2O], have not been previously conducted. Such experiments will improve our understanding of the mobility of uranium and other actinides in natural lithologies as well as provide key information applicable to nuclear waste repository strategies involving Mg-rich phases. Experiments with mineral powders were used to determine the partition coefficients (K d) and coordination of UO22+ during adsorption and co-precipitation with brucite, nesquehonite and hydromagnesite. The K d values for the selected Mg-rich minerals were comparable or greater than those published for calcium carbonates. Extended X-ray absorption fine structure analysis results showed that the structure of the uranyl-triscarbonato [UO2(CO3)3] species was maintained after surface attachment and that uptake of uranyl ions took place mainly via mineral surface reactions.
    Mineralogical Magazine 12/2012; 76(8). DOI:10.1180/minmag.2012.076.8.24 · 2.03 Impact Factor
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    ABSTRACT: The first tetrameric cation-cation neptunyl(v) cluster, [{NpO(2)(salen)}(4)(μ(8)-K)(2)][K(18C6)Py](2), has been synthesized in non-aqueous solution from the reaction of [(NpO(2)Py(5))(KI(2)Py(2))](n) with K(2)salen and its structure determined in the solid state and in solution where the complex retains its tetrameric form.
    Dalton Transactions 06/2012; 41(36):10900-2. DOI:10.1039/c2dt31072d · 4.20 Impact Factor
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    ABSTRACT: The comparative study of chemical reactivity between trivalent late actinides (An) and the lanthanides (Ln) has always been a challenging issue. For that purpose, soft donor ligands (containing for example sulfur atoms or more borderline N atoms) are known to have a relative tendency for higher interaction with the An(III) than with the Ln(III) metal cations. Consequently, thiocyanates have been envisioned as possible ligands for the selective complexation of heavy actinides (namely, Am and Cm) over lanthanides. This paper is an illustration of this approach and reports on the thiocyanate chemistry of lutetium. Three new complexes, 1, [n-(C4H9)4N]3[Lu(NCS)4(NO3)2], 2, K4[Lu(NCS)4(H2O)4](NCS)3(H2O)2 and for comparison 3, K4[Nd(NCS)4(H2O)4](NCS)3(H2O)2 have been characterized by X-ray single crystal diffraction. In addition, dissolution of the nitrato lutetium adduct (1) in wet ethanolsolvent brings some valuable information about the structure of the cation coordination sphere in solution compared to the solid crystalline state. Another point of comparison comes from the dissolution of lutetium nitrate also in wet ethanol. In both cases, the cation's coordination sphere has been probed by IR and EXAFS at the Lu L3 edge. Additional comparison with molecular dynamic simulations of the lutetium-nitrate–ethanol (wet) system has been performed and coupled to the EXAFS data fitting. Upon dissolution of 1 as well as of lutetium nitrate, a decrease of the number of nitrate ligands has been observed. In the case of 1, a clear decrease of the number of thiocyanate ligand coordination has also been observed, leading to a strong rearrangement of the cation polyhedron from solid state to solution.
    New Journal of Chemistry 11/2011; 35(12):2755-2765. DOI:10.1039/C1NJ20494G · 3.09 Impact Factor
  • ChemInform 09/2011; 42(38):no-no. DOI:10.1002/chin.201138016
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    ABSTRACT: The compounds Tl(3)Cu(4)USe(6) and Tl(2)Ag(2)USe(4) were synthesized by the reaction of the elements in excess TlCl at 1123 K. Both compounds crystallize in new structure types, in space groups P2(1)/c and C2/m, respectively, of the monoclinic system. Each compound contains layers of USe(6) octahedra and MSe(4) (M = Cu, Ag) tetrahedra, separated by Tl(+) cations. The packing of the octahedra and the tetrahedra within the layers is compared to the packing arrangements found in other layered actinide chalcogenides. Tl(3)Cu(4)USe(6) displays peaks in its magnetic susceptibility at 5 and 70 K. It exhibits modified Curie-Weiss paramagnetic behavior with an effective magnetic moment of 1.58(1) μ(B) in the temperature range 72-300 K, whereas Tl(2)Ag(2)USe(4) exhibits modified Curie-Weiss paramagnetic behavior with μ(eff) = 3.4(1) μ(B) in the temperature range 100-300 K. X-ray absorption near-edge structure (XANES) results from scanning transmission X-ray spectromicroscopy confirm that Tl(3)Cu(4)USe(6) has Se bonding characteristic of discrete Se(2-) units, Cu bonding generally representative of Cu(+), and U bonding consistent with a U(4+) or U(5+) species. On the basis of these measurements, as well as bonding arguments, the formal oxidation states for U may be assigned as +5 in Tl(3)Cu(4)USe(6) and +4 in Tl(2)Ag(2)USe(4).
    Inorganic Chemistry 06/2011; 50(14):6656-66. DOI:10.1021/ic200565n · 4.76 Impact Factor
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    ABSTRACT: The polymeric complex [(NpO(2)Py(5))(KI(2)Py(2))](n) is prepared from dry "NpO(2)Cl" by anion exchange with potassium iodide in pyridine affording the first convenient starting material for the development of NpO(2)(+) coordination chemistry in anhydrous organic media.
    Chemical Communications 05/2011; 47(19):5497-9. DOI:10.1039/c1cc11010a · 6.83 Impact Factor
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    ABSTRACT: The title compound, (C(16)H(36)N)(3)[Th(NCS)(4)(NO(3))(3)], was obtained from the reaction of Th(NO(3))(4)·5H(2)O with (Bu(4)N)(NCS). The Th(IV) atom is in a ten-coordinate environment of irregular geometry, being bound to the N atoms of the four thio-cyanate ions and to three bidentate nitrate ions. The average Th-N and Th-O bond lengths are 2.481 (10) and 2.57 (3) Å, respectively.
    Acta Crystallographica Section E Structure Reports Online 04/2011; 67(Pt 4):m487. DOI:10.1107/S1600536811009792 · 0.35 Impact Factor
  • MRS Online Proceeding Library 01/2011; 1107. DOI:10.1557/PROC-1107-347
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    ABSTRACT: Electrospray ionization quadrupole ion trap mass spectrometry (ESI-QIT/MS) of the ammonium cerium(III) phosphomolybdate complex (NH4)11[Ce(III)(PMo11O39)2] in aqueous media has revealed a concentration-dependent behavior. Under fixed instrumental parameters, the Ce-containing polyoxomolybdate complexes H2Ce(III)P2Mo22O753− and Ce(III)PMo11O382− are the primary species present at 11mM (pH=4.3); at 0.7mM (pH=3.6), Ce(III)PMo10O352− is the predominant species, Ce(III)PMo11O382− is quite diminished, and H2Ce(III)P2Mo22O753− is absent. As a result of the complex isotopic fingerprints from multiple molybdenums, compositions of such ions are difficult to assign—successive collision induced dissociation (CID) of large ions produced smaller ions for which calculated and experimental isotopic patterns could be compared. The oxidation state of Ce and the number of counter cations on negative complexes was discerned from spectra of ions containing 1H+ and 7Li+. The overall result is an ESI method applicable to phosphomolybdate complexes containing redox sensitive f-block metal ions such as Ce(IV) and Pu(III/IV). Dissociation studies also gave insight into favored fragmentation pathways, and generated gas ions with empirical formulae similar to known condensed-phase ions. Deconvolution of concentration- and pH-dependent solution behavior via ESI/MS and 31P NMR spectroscopy showed speciation dependent on solution concentration, not on pH.
    International Journal of Mass Spectrometry 01/2011; 299(1):35-46. DOI:10.1016/j.ijms.2010.09.015 · 1.97 Impact Factor
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    ABSTRACT: Electrospray ionization quadrupole ion trap mass spectrometry of the ammonium lanthanide(III) phosphomolybdate complex (NH4)11Ce(III)(PMo11O39)2 has been conducted revealing the Ce-POM complexes H2Ce(III)P2Mo22O753- and Ce(III)PMo11O382- as the primary Ce species in 10 mM solutions. From the complex isotopic fingerprints produced through the assembly of multiple molybdenum atoms, a transition metal with seven naturally occurring isotopes, the identities of larger ions were confirmed via successive collision induced dissociation (CID) studies of the gas phase ions. The result of these CID studies was the production of smaller ions with reduced molybdenum content, allowing for comparison between calculated and experimental isotopic distributions. CID studies also provided insights into favored fragmentation pathways. These studies provide a basis to explore speciation and ESI behavior of actinide cluster complexes.
    MRS Online Proceeding Library 01/2011; 1264. DOI:10.1557/PROC-1264-Z02-02
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    ABSTRACT: The nature of the reactivity of the "yl" oxygens has been a subject of constant interest for a long time in uranyl chemistry. Thus, the electron-donor ability of the equatorial ligands plays an important role in the nature of the uranyl U=O bond. In this paper, a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and both ground-state and time-dependent density functional theory (DFT) calculations have been used to examine the effect of equatorial plane ligation on the U=O bonding in two uranyl complexes: [UO(2)(py)(3)I(2)] and [UO(2)(CN)(5)][NEt(4)](3). By coupling experimental data and theory, spectral features observed in the oxygen K-edge NEXAFS spectra have been assigned. Despite the inert character of the U=O bond, we observe that the electron-donating or withdrawing character of the equatorial ligands has a measurable effect on features in the NEXAFS spectra of these species and thereby on the unoccupied molecular orbitals of {UO(2)}(2+).
    Physical Chemistry Chemical Physics 09/2010; 12(42):14253-62. DOI:10.1039/c0cp00386g · 4.49 Impact Factor
  • ChemInform 07/2010; 41(27). DOI:10.1002/chin.201027003
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    ABSTRACT: The compound La(2)U(2)Se(9) was obtained in high yield from the stoichiometric reaction of the elements in an Sb(2)Se(3) flux at 1123 K. The compound, which crystallizes in a new structure type in space group Pmma of the orthorhombic system, has a three-dimensional structure with alternating U/Se and La/Se layers attached via three independent, infinite polyselenide chains. The U atom has a monocapped square antiprismatic coordination of Se atoms, whereas one La atom is bicapped square prismatic and the other La atom is trigonal prismatic. La(2)U(2)Se(9) displays an antiferromagnetic transition at T(N) = 5 K; above 50 K, the paramagnetic behavior can be fit to the Curie-Weiss law, yielding a mu(eff) of 3.10(1) mu(B)/U. The low-temperature specific heat of La(2)U(2)Se(9) exhibits no anomalous behavior near the Neel temperature that might indicate long-range magnetic ordering or a phase transition. X-ray absorption near-edge structure (XANES) spectra have confirmed the assignment of formal oxidation states of +III for lanthanum and +IV for uranium in La(2)U(2)Se(9).
    Inorganic Chemistry 02/2010; 49(5):2568-75. DOI:10.1021/ic902503n · 4.76 Impact Factor
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    ABSTRACT: The smuggling of nuclear material and the diversion of fissile material for covert weapon programs both present grave risks to world security. Methods are needed to detect nuclear material smuggled in cargo, and for proper material accountability in civilian fuel re-processing facilities. Nuclear resonance fluorescence (NRF) is a technique that can address both needs. It is a non-destructive active interrogation method that provides isotope-specific information. It works by using a gamma-ray beam to resonantly excite levels in a nucleus and observing the gamma-rays emitted whose energy and intensity are characteristic of that isotope. ^237Np presents significant safeguard challenges; it is fissile yet currently has fewer safeguard restrictions. NRF measurements on ^237Np will expand the nuclear database and will permit designing interrogation and assay systems. Measurements were made using the bremsstrahlung beam at the HVRL at MIT on a 7 g target of ^237Np with two incident electron energies of 2.8 and 3.1 MeV. Results will be presented with discussion of the relevant nuclear structure necessary to predict levels in other actinides.
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    ABSTRACT: Reaction of (CpSiMe(3))(3)U or (CpSiMe(3))(3)Nd with (Cp*Al)(4) or Cp*Ga (Cp* = C(5)Me(5)) afforded the isostructural complexes (CpSiMe(3))(3)M-ECp* (M = U, E = Al (1); M = U, E = Ga (2); M = Nd, E = Al (3); M = Nd, E = Ga (4)). In the case of 1 and 2 the complexes were isolated in 39 and 90% yields, respectively, as crystalline solids and were characterized by single-crystal X-ray diffraction, variable-temperature (1)H NMR spectroscopy, elemental analysis, variable-temperature magnetic susceptibility, and UV-visible-NIR spectroscopy. In the case of 3 and 4, the complexes were observed by variable-temperature (1)H NMR spectroscopy but were not isolated as pure materials. Comparison of the equilibrium constants and thermodynamic parameters DeltaH and DeltaS obtained by (1)H NMR titration methods revealed a much stronger U-Ga interaction in 2 than the Nd-Ga interaction in 4. Competition reactions between (CpSiMe(3))(3)U and (CpSiMe(3))(3)Nd indicate that Cp*Ga selectively binds U over Nd in a 93:7 ratio at 19 degrees C and 96:4 at -33 degrees C. For 1 and 3, comparison of (1)H NMR peak intensities suggests that Cp*Al also achieves excellent U(III)/Nd(III) selectivity at 21 degrees C. The solution electronic spectra and solid-state temperature-dependent magnetic susceptibilities of 1 and 2, in addition to X-ray absorption near-edge structure (XANES) measurements from scanning transmission X-ray microscopy (STXM) of 1, are consistent with those observed for other U(III) coordination complexes. DFT calculations using five different functionals were performed on the model complexes Cp(3)M-ECp (M = Nd, U; E = Al, Ga), and empirical fitting of the values for Cp(3)M-ECp allowed the prediction of binding energy estimates for Cp*Al compounds 1 and 3. NBO/NLMO bonding analyses on Cp(3)U-ECp indicate that the bonding consists predominantly of a E-->U sigma-interaction arising from favorable overlap between the diffuse ligand lone pair and the primarily 7s/6d acceptor orbitals on U(III), with negligible U-->E pi-donation. The overall experimental and computational bonding analysis suggests that Cp*Al and Cp*Ga behave as good sigma-donors in these systems.
    Journal of the American Chemical Society 09/2009; 131(38):13767-83. DOI:10.1021/ja904565j · 12.11 Impact Factor
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    ABSTRACT: We report the structural, spectroscopic and preliminary magnetic characterisation of a tri-metallic plutonyl(VI) polyoxometalate complex, K(11)[K(3)(PuO(2))(3)(GeW(9)O(34))(2)] x 12 H(2)O.
    Dalton Transactions 08/2009; DOI:10.1039/b908648j · 4.20 Impact Factor
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    ABSTRACT: We report the synthesis, spectroscopic and structural characterization, and computational analysis of a series of phosphomolybdate complexes with tetravalent metal cations. The reaction between Ce (IV) and Th (IV) with phosphomolybdate at the optimum pH for the stabilization of the lacunary heteropolyoxometalate anion, [PMo 11O 39] (7-), results in the formation of compounds containing the anions [Ce(PMo 11O 39) 2] (10-) and [Th(PMo 11O 39) 2] (10-), respectively. Single crystal X-ray diffraction analysis was performed on salts of both species, Cs 10[Ce(PMo 11O 39) 2].20H 2O and (NH 4) 10[Th(PMo 11O 39) 2].22H 2O. In both anionic complexes the f-block metal cation is coordinated to the four unsaturated terminal lacunary site oxygens of each [PMo 11O 39] (7-) anion, yielding 8 coordinate sandwich complexes, analogous to previously prepared related complexes. Spectroscopic characterization points to the stability of these complexes in solution over a reasonably wide pH range. Density functional analysis suggests that the Ce-O bond strength in [Ce(PMo 11O 39) 2] (10-) is greater than the Th-O bond strength in [Th(PMo 11O 39) 2] (10-), with the dominant bonding interaction being ionic in both cases. In contrast, under similar reaction conditions, the dominant solid state Zr (IV) and Hf (IV) complexes formed contain the anions [Zr(PMo 12O 40)(PMo 11O 39)] (6-) and [Hf(PMo 12O 40)(PMo 11O 39)] (6-), respectively. In these complexes the central Group 4 d-block metal cations are coordinated to the four unsaturated terminal lacunary site oxygens of the [PMo 11O 39] (7-) ligand and to four bridging oxygens of a plenary Keggin anion, [PMo 12O 40] (3-). In addition, (NH 4) 5{Hf[PMo 12O 40][(NH 4)PMo 11O 39]}.23.5H 2O can be crystallized as a minor product. The structure of the anion, {Hf[PMo 12O 40][(NH 4)PMo 11O 39]} (5-), reveals coordination of the central Hf (IV) cation via four bridging oxygens on both the coordinated [PMo 11O 39] (7-) and [PMo 12O 40] (3-) anions. Unusually, the highly charged lacunary site remains uncoordinated to the Hf metal center but instead interacts with an ammonium cation. (31)P NMR indicates that complexation of the Keggin anion, [PMo 12O 40] (3-), to Hf (IV) and Zr (IV) will stabilize the Keggin anion to a much higher pH than usually observed.
    Inorganic Chemistry 08/2008; 47(13):5787-98. DOI:10.1021/ic800101t · 4.76 Impact Factor

Publication Stats

225 Citations
93.42 Total Impact Points


  • 2009–2014
    • University of California, Berkeley
      Berkeley, California, United States
  • 2011–2012
    • Cea Leti
      Grenoble, Rhône-Alpes, France
  • 2010
    • Northwestern University
      • Department of Chemistry
      Evanston, Illinois, United States
  • 2005–2009
    • The University of Manchester
      • Centre for Radiochemistry Research (CRR)
      Manchester, England, United Kingdom