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Cation-cation interactions, magnetic communication and reactivity of the pentavalent uraniumion [U(NR)2]+

Description: The dimeric bis(imido) uranium complex [{l_brace}U(NtBu)2(I)(tBu2bpy){r_brace}2] (see picture; U green, N blue, I red) has cation-cation interactions between [U(NR)2]+ ions. This f1-f1 system also displays f orbital communication between uranium(V) centers at low temperatures, and can be oxidized to generate uranium(VI) bis(imido) complexes.
Date: January 1, 2009
Creator: Spencer, Liam P; Schelter, Eric J; Boncella, James M; Yang, Ping; Gsula, Robyn L; Scott, Brian L et al.
Partner: UNT Libraries Government Documents Department

quantifying and Predicting Reactive Transport

Description: This project was led by Dr. Jiamin Wan at Lawrence Berkeley National Laboratory. Peter Burns provided expertise in uranium mineralogy and in identification of uranium minerals in test materials. Dr. Wan conducted column tests regarding uranium transport at LBNL, and samples of the resulting columns were sent to Dr. Burns for analysis. Samples were analyzed for uranium mineralogy by X-ray powder diffraction and by scanning electron microscopy, and results were provided to Dr. Wan for inclusion in the modeling effort. Full details of the project can be found in Dr. Wan's final reports for the associated effort at LBNL.
Date: December 4, 2009
Creator: Burns, Peter C.
Partner: UNT Libraries Government Documents Department

THE CRYSTAL STRUCTURE OF RbU$sub 6$F$sub 2$$sub 5$

Description: The compound RbU/sub 6/F/sub 25/ has a hexagonal crystal structure with the parameters a/sub o/ = 8.195 plus or minus 0.002 A and c/sub o/ = 16.437 plus or minus 0.002 A. This compound is believed to be isomorphous to KU/sub 6/F/sub 25/ and KTh/sub 6/F/sub 25/. (auth) uranium hexafluoride -chlorine trifluoride -hydrogen fluoride from a knowledge of the behavior of the three binary systems. The conditions under which chlorine trifluoride and hydrogen fluoride could be removed from uranium hexafluoride by fractional distillation are discussed. (auth)
Date: May 15, 1958
Creator: Harris, L.A.
Partner: UNT Libraries Government Documents Department

Trivalent metallocene chemistry of some uranium, titanium, and zirconium complexes

Description: Dicyclopentadienyluranium halide dimers have been prepared and their solution behavior examined. These molecules exist as dimers in solution, and the halide ligands undergo rapid site exchange on the NMR timescale above 50 C. Analogous dicyclopentadienyluranium hydroxide dimers have also been prepared; they oxidatively eliminate hydrogen to give the corresponding oxide dimers. Mechanism of this reaction is consistent with {alpha}migration of one of the hydroxide hydrogen atoms to a uranium center followed by elimination of hydrogen. Ground state of [(Me{sub 3}Si){sub 2}C{sub 5}H{sub 3}]{sub 3}M M = Nd, U and their base adducts has been examined by variable temperature magnetic susceptibility and EPR spectroscopy. The ground state is found to be {sup 4}I{sub 9/2} with a crystal field state consisting largely of J{sub z} = 1/2 lowest, in agreement with previous studies on tris-cyclopentadienylneodymium complexes. The zirconium metallocene Cp{sub 3}Zr has been prepared, characterized crystallographically, and its reactivity studied. Its chemical behavior is controlled by presence of an electron in the non-bonding, d{sub z}2 orbital which prevents formation of base adducts Of Cp{sub 3}Zr, but allows Cp{sub 3}Zr to abstract atoms from other molecules. Electonic and EPR spectra of Cp*{sub 2}TiX complexes, where Cp* is Me{sub 5}C{sub 5} and X is a monodentate, anionic ligand such as halide, have been studied. A {pi}-bonding spectrochemical series is developed, and trends in {pi}-bonding ability are found similar to those in other inorganic complexes. The {beta}-agostic interactions in Cp*{sub 2}TiN(Me)Ph have been examined using variable temperature EPR spectroscopy, and the enthalpy/entropy of the interaction determined. In Cp*{sub 2}TiEt, enthalpy of the {beta}-agostic interaction is {minus}1.9 kcal/mol. The titanocene anion, Cp*{sub 2}TiLi(TMEDA) (TMEDA is N,N,N`,N`-tetramethylethylenediamine), has been prepared and its structure determined.
Date: May 1, 1995
Creator: Lukens, W. W., Jr.
Partner: UNT Libraries Government Documents Department

Uranium (VI)Bis(imido) chalcogenate complexes:synthesis and density functional theory analysis

Description: Bis(imido) uranium(VI) trans- and cis-dichalcogenate complexes with the general formula U(NtBu)2(EAr)2(OPPh3)2 (EAr = O-2-tBuC6H4, SPh, SePh, TePh) and U(NtBu)2(EAr)2(R2bpy) (EAr = SPh, SePh, TePh) (R2bpy = 4,4'-disubstituted-2,2'-bipyridyl, R = Me, tBu) have been prepared. This family of complexes includes the first reported monodentate selenolate and tellurolate complexes of uranium(VI). Density functional theory calculations show that covalent interactions in the U-E bond increase in the trans-dichalcogenate series U(NtBu)2(EAr)2(OPPh3)2 as the size of the chalcogenate donor increases and that both 5f and 6d orbital participation is important in the M-E bonds of U-S, U-Se, and U-Te complexes.
Date: January 1, 2009
Creator: Spencer, Liam P; Batista, Enrique R; Boncella, James M; Yang, Ping & Scott, Brian L
Partner: UNT Libraries Government Documents Department

Novel complexing agents for the efficient separation of actinides and remediation of actinide-contaminated sites

Description: Research into the coordination chemistry of transactinide elements should provide us with new fundamental knowledge about structure, geometry, and stability of these metal complexes. Our approach involves the design, synthesis, and characterization of {open_quotes}expanded porphyrin{close_quotes} macrocyclic ligands which coordinate the actinide metal cations with high thermodynamic affinity and kinetic stability. We can use the knowledge from understanding the fundamental coordination chemistry of these elements as a stepping stone to heavy metal detoxification, radioactive waste cleanup, and possibly radioactive isotope separation. The critical components of this research endeavor, along with the viability of metal complex formation, will be correlated to ring size and core geometry of the ligand and, the atomic radius, oxidation state, coordination geometry and coordination number of the transactinium metal ion. These chelating agents may have certain applications to the solution of some radioactive waste problems if they can be attached to polymer supports and used to chemically separate the radioactive components in waste.
Date: March 15, 1996
Creator: Baisden, P. & Kadkhodayan, B.
Partner: UNT Libraries Government Documents Department

Noble reactions for the actinides: safe gold-based access to organouranium and azide complexes

Description: Gold has had a profound impact on organic chemistry; its compounds are spectacular catalysts for many organic transformations involving the formation of C-C, C-O, C-N and CoS bonds, and have enabled unprecedented pathways for the functionalization of C-H and C-C bonds. In general, gold complexes have not been exploited as reagents in organometallic or inorganic chemistry, although a few gold(l) aryl and alkynyl compounds have been reported to undergo transmetalation with transition metal complexes. We have been developing methods for functionalizing uranium complexes and have shown that Cu(l)-X reagents effect the oxidation of uranium with formation of U-X bonds, providing easy chemical control over uranium in oxidation states ranging from U{sup III}{yields}U{sup VI}. Although a logical approach for the direct generation of U-carbon and U-azide bonds, this Cu-based platform is limited in scope as it only works for pure and isolable copper compounds. This is problematic given the instability of organocuprates and copper azides, which can detonate violently as isolated solids. As such, this route has been confined to the synthesis of select uranium phenylacetylide complexes. Over the past few years, a variety of stable gold(l) alkyl, alkenyl, aryl, alkynyl, and azide complexes have been reported, propelling us to investigate their potential as reagents within the oxidative functionalization platform. Unlike the related CU{sup I} systems, Au{sup I} reagents are easily derivatized, and are safe to handle and isolate. Herein, we report that gold(l)-phosphine compounds can undergo a new class of reaction, and are excellent reagents for the oxidative functionalization of uranium with azide and carbon anions.
Date: January 1, 2008
Creator: Thomson, Robert K.; Graves, Christopher R.; Scott, Brian L. & Kiplinger, Jaqueline L.
Partner: UNT Libraries Government Documents Department

SOLUBILITIES OF URANYL AND IRON(III) DIBUTYL AND MONOBUTYL PHOSPHATES IN TBP SOLVENT EXTRACTION SOLUTIONS

Description: The solubilities of uranyl dlbutyl phosphate, uranyl monobutyl phosphate, ferric dibutyl phosphate, and ferric monobutyl phosphate were measured in aqueous nitric acid solutions ranging from 0 to 3 M and in 30% TBP in Amsco 125-82 solution containing 0--0.7 M HNO/sub 3/. For the respective compounds in the aqueous phases, as the acidity increased from 0 to 3 M, the solubilities increased from 0.004 to 0.7 g U/liter, O.O5to 50 g U/liter, <1 to 30 mg Fe(III)/ liter, and 0.003 to 3 g Fe(III)/liter; corresponding solubilities in the organic phases increased with acidity from 14 to 165 g U/liter, 11 to 110 g U/liter, <O.5to 4 mg Fe(III)/liter, and <0.002 to 1.5 g Fe(III)/liter. All these compounds foamed or formed very flocculent solids in the aqueous phases snd tended to settle slowly in the organic phases and rise to the surface in the aqueous phases, suggesting that they would be interface seekers in two-phase aqueousorganic systems. (auth)
Date: May 1, 1961
Creator: Davis, W. Jr.
Partner: UNT Libraries Government Documents Department

Structure of Pentakis(urea)dioxouranium(VI)Nitrate, [UO2 (OC(NH2)2)5] (NO3)2

Description: In our ongoing studies of uranium complexes we have determined the crystal structure of UO{sub 2}(urea){sub 5}(NO{sub 3}){sub 2} by X-ray diffraction. Gentile and Campisi reported the preparation of this compound and concluded, on the basis of infrared spectra, that the nitrate groups are not coordinated to uranium, a fact which we confirm. The uranyl ion is coordinated by oxygen atoms of the five urea molecules in a complex which is monomeric, not a polymer as suggested earlier. From an aqueous solution of uranyl nitrate and urea which was allowed to evaporate slowly overnight, small fluorescent lime-green crystals precipitated. The crystals were stable in air and showed no decomposition during the two weeks the X-ray experiments were being conducted. Weissenberg photography showed the crystal to be monoclinic, and rough cell dimensions were obtained.
Date: August 1, 1978
Creator: Zalkin, Allan; Ruben, Helena & Templeton, David H.
Partner: UNT Libraries Government Documents Department

Metal-ligand ``multiple`` bonding: Revelations in the electronic structure of complexes of high-valent f-elements

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of this project has been to extend the understanding of the nature of interactions between f-metals and first row elements (important both in natural systems and in ceramics), as well as providing important new information regarding basic differences in the chemical nature of d- and f-metals. By developing preparative routes to novel classes of early actinide and lanthanide complexes in which metal-ligand bonding is formally unsaturated, this project has provided the means to study orbital interactions and charge distribution in these species by physical, chemical, and theoretical means. Evaluation of the physical and chemical characteristics of these species is providing dramatic evidence for the involvement of valence metal orbitals [nf and (n+1)d] in bonding, and is yielding new insights into the factors influencing stability of related species.
Date: July 1, 1997
Creator: Burns, C.J.; Arney, D.S.J.; Schnabel, R.C.; Warner, B.P.; Bursten, B.E.; Green, J.C. et al.
Partner: UNT Libraries Government Documents Department

A Thermodynamic Model for Acetate, Lactate, and Oxalate Complexation with Am(III), Th(IV), Np(V), and U(VI) Valid to High Ionic Strength

Description: The organic ligands acetate, lactate, oxalate and EDTA have been identified as components of wastes targeted for disposal in the Waste Isolation Pilot Plant (WIPP) located in Southeastern New Mexico. The presence of these ligands is of concern because complexation of the actinides with the ligands may increase dissolved actinide concentrations and impact chemical retardation during transport. The current work considers the complexation of Am(III), Th (IV), Np(V), and U(W) with two of the organic ligands, acetate and lactate, in NaCl media from dilute through high concentration. A thermodynamic model for actinide complexation with the organic ligands has been developed based on the Pitzer activity coefficient formalism and the Harvie-Moller-Weare, Felmy-Weare database for describing brine evaporite systems. The model was parameterized using first apparent stability constant data from the literature. Because of complexation of other metal ions (Fe, Mg, Ni, Pb, etc.) present in the WIPP disposal room with the organic ligands, preliminary results from model calculations indicate the organic ligands do not significantly increase dissolved actinide concentrations.
Date: January 15, 1999
Creator: Bynaum, R.V.; Free, S.J. & Moore, R.C.
Partner: UNT Libraries Government Documents Department

Spectroscopic studies of U(VI) sorption at the kaolinite-water interface. Final report

Description: Efficient use of U as a resource and safe handling, recycling and disposal of U-containing wastes require an understanding of the factors controlling the fate of U, where fate refers to the destination of U, typically expressed as an environmental medium or a process phase. The sorption process constitutes a change in elemental fate. Partitioning of an element from solution to a solid phase, or sorption, can be divided into three broad categories: adsorption, surface precipitation, and absorption. Extended X-ray absorption fine structure (EXAFS), a type of X-ray absorption spectroscopy (XAS), offers the possibility for distinguishing among different modes of sorption by characterizing the atomic environment of the sorbing element. In this study, the authors use EXAFS to determine the structure of U(VI) sorption complexes at the kaolinite-water interface. In Chapter One, they present an overview of selected aspects of U structural chemistry as a basis for considering the structural environment of U at the solid-water interface. To evaluate the utility of XAS for characterization of the structural environment of U(VI) at the solid-water interface, they have carried out an in-depth analysis of XAS data from U(VI)-containing solid and solution model compounds, which they describe in Chapter Two. In Chapter three, they consider sorption of U by kaolinite as a means of effecting the removal of U from surface collection pond waters on the Rocky Flats Plant site in northern Colorado.
Date: June 1, 1994
Creator: Thompson, H.A.; Parks, G.A. & Brown, G.E. Jr.
Partner: UNT Libraries Government Documents Department

Tris(bis(trimethylsilyl)amido)uranium: Compounds with tri-, tetra-, and penta-valent uranium

Description: This trivalent uranium compound, serves as a precursor to new tri-, tetra-, and penta-valent uranium species. The geometry about the U atom is pyramidal. Lewis-base coordination compounds of U(N(SiMe/sub 3/)/sub 2/)/sub 3/ with a one-to-one- ratio of Lewis base to uranium were isolated with pyridine, 4-dimethylamino-pyridine, 2,6-Me/sub 2/-C/sub 6/H/sub 3/NC, and TPO. Two-to-one coordination compounds were obtained with t-butylnitrile and t-butylisocyanide. Compounds with more sterically demanding bases could not be isolated. The expected decrease in U-N(SiMe/sub 3/)/sub 2/ bond length with increase in oxidation state is not observed. Reaction of ClU(N(SiMe/sub 3/)/sub 2/)/sub 3/and Li(NH(p-tolyl)) yields the uranium (IV) dimer, U/sub 2/(N(SiMe/sub 3/)/sub 2/)/sub 4/(..mu..-N(p-tolyl))/sub 2/. Reaction with 2,4,6-triemethylaniline produces a dimer. Analogous substitution products could not be obtained with aniline or p-toluidine. t-Bu/sub 3/CO/sup /minus//, t-Bu/sub 2/CHO/sup /minus//, and t-Bu/sub 3/SiO/sup /minus// are used to synthesize new tetravalent, mononuclear uranium compounds. Reaction of ClU(tritox)/sub 3/ with alkyllithium reagents leads to isolation of RU(tritox)/sub 3/. The reaction of U(ditox)/sub 4/ with MeLi affords the addition product U(ditox)/sub 4/(Me)Li, whose crystal structure is described. Preparation of uranium silox compounds is reported. 97 refs., 26 figs., 39 tabs.
Date: April 1, 1988
Creator: Stewart, J.L.
Partner: UNT Libraries Government Documents Department

Separation of trace uranium from plutonium for subsequent analysis

Description: Trace uranium quantities are separated from plutonium metal and plutonium oxide for subsequent analysis. Samples are dissolved in hydrobromic acid or a hydrobromic acid-hydrofluoric acid mixture. The U(VI)-halide complex is separated from nonsorbed Pu(III) on an anion exchange column using sequential washes of 9M HBr, a 0.1M HI-12M HCl mixture and 0.1M HCl.
Date: August 1, 1980
Creator: Marsh, S.F.
Partner: UNT Libraries Government Documents Department

X-ray-diffraction studies of the structures of organic-phase solvent-extraction complexes

Description: Structures were determined of the complexes which form when the uranyl ion is extracted from nitric acid solutions with organophosphorus reagents: UO/sub 2/(TBPO)/sub 2/(NO/sub 3/)/sub 2/, UO/sub 2/(TiBP)/sub 2/(NO/sub 3/)/sub 2/, UO/sub 2/(DBP)/sub 2/, and UO/sub 2/(DBP)(TBPO)NO/sub 3/. (TiBP = tri-isobutyl phosphate.) (DLC)
Date: January 1, 1983
Creator: Burns, J.H.
Partner: UNT Libraries Government Documents Department

New insights into uranium (VI) sol-gel processing

Description: Nuclear Magnetic Resonance (NMR) investigations on the Oak Ridge National Laboratory process for sol-gel synthesis of microspherical nuclear fuel (UO{sub 2}), has been extremely useful in sorting out the chemical mechanism in the sol-gel steps. {sup 13}C, {sup 15}N, and {sup 1}H NMR studies on the HMTA gelation agent (Hexamethylene tetramine, C{sub 6}H{sub 12}N{sub 4}) has revealed near quantitative stability of this adamantane-like compound in the sol-gel process, contrary to its historical role as an ammonia source for gelation from the worldwide technical literature. {sup 17}O NMR of uranyl (UO{sub 2}{sup ++}) hydrolysis fragments produced in colloidal sols has revealed the selective formation of a uranyl trimer, ((UO{sub 2}){sub 3}({mu}{sub 3}-O)({mu}{sub 2}-OH){sub 3}){sup +}, induced by basic hydrolysis with the HMTA gelation agent. Spectroscopic results will be presented to illustrate that trimer condensation occurs during sol-gel processing leading to layered polyanionic hydrous uranium oxides in which HMTAH{sup +} is occluded as an intercalation'' cation. Subsequent sol-gel processing of microspheres by ammonia washing results in in-situ exchange and formation of a layered hydrous ammonium uranate with a proposed structural formula of (NH{sub 4}){sub 2} ((UO{sub 2}){sub 8} O{sub 4} (OH){sub 10}) {center dot} 8H{sub 2}O. This compound is the precursor to sintered UO{sub 2} ceramic fuel. 23 refs., 10 figs.
Date: January 1, 1990
Creator: King, C.M.; Thompson, M.C.; Buchanan, B.R. (Westinghouse Savannah River Co., Aiken, SC (USA)); King, R.B. (Georgia Univ., Athens, GA (USA). Dept. of Chemistry) & Garber, A.R. (South Carolina Univ., Columbia, SC (USA). Dept. of Chemistry)
Partner: UNT Libraries Government Documents Department

Speciation of uranium(VI) sorption complexes on montmorillonite

Description: Environmental contaminant releases that contain uranium are among the most serious problems that must be confronted by restoration programs. To facilitate restoration, information concerning the speciation of uranium is needed. Under oxidizing conditions, dissolved uranium is predominantly in the U(VI) (uranyl) form and is quite mobile in the environment, however sorption onto soils may retard its movement. In this study, we have investigated the effects of changes in solution speciation on the nature of uranyl sorption complexes on montmorillonite, a common soil constituent. Aqueous U(VI) solutions between pH 3 to 7 were batch-equilibrated with montmorillonite for several days; specific pH values were selected such that the solutions consisted of dominantly monomeric, oligomeric, or a mix of monomeric and oligomeric aqueous uranyl species. Emission spectroscopy was used to investigate the nature of U(VI) sorbed to montmorillonite.
Date: January 1, 1992
Creator: Chisholm-Brause, C.J.; Morris, D.E. (Los Alamos National Lab., NM (United States)) & Richard, R.E. (Fort Lewis Coll., Durango, CO (United States). Dept. of Chemistry)
Partner: UNT Libraries Government Documents Department

Microcalorimetric measurement of reaction enthalpies in solutions of uranium and neptunium compounds

Description: The formation of complexes of uranyl and neptunyl(VI) ions with carbonate and hydrogen carbonate has been studied by titration microcalorimetry. The measurements were carried out with a computer-controlled microcalorimeter which is described in detail. Sample volumes are typically in the range of 1.5 to 2.5 ccm, containing about 0.05 millimole of the ionic species to be studied. The small volume renders the calorimeter useful for the measurement of uncommon and strongly radioactive substances. Enthalpies of reaction were obtained for the formation of the dicarbonato and the tricarbonato uranyl ions in a sulfate medium of ionic strength 1.6. The enthalpies are ..delta..H/sub 2/ = -39.6 +- 1 kJ/mol and -57.5 +- 1.5 kJ/mol, respectively. The titration data for the neptunyl(VI) - carbonate system yield a value of -50 +- 2 kJ/mol for the tricarbonato-neptunyl ion when interpreted in analogy to the uranyl system.
Date: January 1, 1984
Creator: Schreiner, F.; Friedman, A.M.; Richards, R.R. & Sullivan, J.C.
Partner: UNT Libraries Government Documents Department