Chemistry Division

Heavy Element Chemistry Research

Investigator(s)	Beitz, J.V.;Nash, K.L.; Soderholm, L.; Jensen, M.P.; Liu, G.K.; Morss, L.R.			$1,743,000
Phone	630-252-7393
E-mail	nash@anlchm.chm.anl.gov

The central emphasis of this program is to develop an understanding of the fundamental chemical and physical properties of f-elements which characterize their interactions with the surrounding environment. One goal is to understand the mechanisms by which f electrons influence the properties of materials containing them. The unique thrust of this effort is to utilize the specific properties of different f elements to alter the electronic behavior of a substance. Basic knowledge obtained from these experiments will be used to design materials with predetermined electronic and cooperative properties for use in such widely diverse physical applications as optical switches, electrical conductors, and catalysts. In parallel research, the electronic and magnetic properties of the heavy elements are probed, using laser-based methods that include optically detected nuclear magnetic resonance and photochemical studies, and modeled in order to attain predictive insight. The understanding achieved is applied to important fundamental and technological issues throughout the nuclear fuel cycle, for example, as a basis for new methods for the decontamination of uranium enrichment plants. A third thrust involves investigation of actinide behavior in solution phases using a variety of spectroscopic, electrochemical, and thermochemical techniques. Combined results from thermodynamic, kinetic, X-ray diffraction, spectroscopic, and molecular modeling experiments are used to characterize the solution/coordination chemistry of actinides in all oxidation states, and the interaction of the metal ions and their complexes with aqueous and organic solvents.

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Chemistry Division

An Actinide Facility for Synchrotron Research in Molecular and Environmental Sciences

Investigator(s)	Soderholm, L.			$240,000 Operating $150,000 Equipment
Phone	630-252-4364
E-mail	soderholm@anlchm.chm.anl.gov

The state-of-the-art beamlines currently under construction at the Advanced Photon Source (APS) will be able to perform an enormous variety of experiments. The goal of this Actinide Facility is to make the largest number of beamlines accessible to experiments involving radioactive samples, and to do so with the least amount of effort on the part of either the experimenter or the targeted-beamline personnel. Funded by a DOE-Facilities Initiative, the Chemistry division at Argonne National Laboratory will make available presently existing, dedicated hot-laboratory facilities to researchers wishing to conduct experiments on actinide-containing samples at the APS. The hot-laboratory space will be provided for simple chemical and physical manipulations of samples before and after experiments. In addition, specialty equipment will be available, both in the form of safety monitoring devices to be used at the hutches, as well as equipment necessary for performing experiments. One example is a purpose-built portable glovebox that can be loaded in the hot-laboratory, and used at the beamline to permit sample manipulations. In addition to equipment, there will also be personnel available for consultation on both the experimental and safety aspects of the experiments. This Facility is driven by members of both the synchrotron community and the actinide community who wish to take advantage of the APS to conduct state-of-the-art research.

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Chemical Sciences Division

Actinide Chemistry

Investigator(s)	Edelstein, N.M.; Andersen, R.A.; Raymond, K.N.; Shuh, D.K.			$1,465,000
Phone	510-486-5624
E-mail	nmedelstein@lbl.gov

Development of new technologies for the use, safe handling, storage, and disposal of actinide materials relies on further understanding of basic actinide chemistry and the availability of trained personnel. This research program is a comprehensive, multifaceted approach to actinide chemistry and to the training of students to address future issues. Research efforts include synthetic chemistry to develop new chemical reagents and actinide materials, their chemical and physical elucidation through characterization techniques, and thermodynamic/kinetic studies for evaluation of complex formation. One aspect is the development of complexing agents that specifically sequester actinide ions for the decorporation of actinides in humans and for the separation of actinides in the environment. Extensive studies are underway to prepare organometallic and coordination compounds of the f-block elements that show the differences and similarities among the f-elements and between the f- and d-transition series elements. Interpretation of optical and magnetic studies on actinide ions in ionic and molecular solids gives information about electronic properties as a function of atomic number. X-ray absorption spectroscopy techniques at the Stanford Synchrotron Radiation Laboratory are employed to investigate both the fundamental and environmental chemistry of transuranic and fission product materials. Soft x-ray synchrotron radiation at the Advanced Light Source is being utilized to characterize actinide solid-state materials.

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Chemical Sciences Division

Actinide/Environmental Beamline User Facility at the Advanced Light Source

Investigator(s)	Shuh, D.K.; Bucher, J.J.; Edelstein, N.M.			$61,000 Operating $92,000 Equipment
Phone	510-486-6937
E-mail	dkshuh@lbl.gov

The Actinide/Environmental Endstation project addresses the utilization of the Advanced Light Source (ALS) for synchrotron investigations of actinide and environmental science in the vacuum ultra-violet/soft x-ray spectral region. The tunability of the photon source permits the use of absorption techniques, optimization of cross-sectional effects for photoemission measurements, and the ability to change electron escape lengths. In order to make measurements on extremely small single crystals, thin film materials, particulates, and on a wide range of radioactive samples from waste sites, it is necessary to work with samples which are substantially more radioactive than can be handled in a general user beamline endstation at the ALS. The characteristics of the photon beam from ALS beamlines (tunability, brightness, flux, and stability) are paramount in transuranium/environmental research because they allow the use of exceptionally small samples, which greatly reduce safety concerns. A dedicated experimental user endstation is being constructed for the investigation of radioactive/hazardous materials to exploit the available beamtime on existing beamlines and to permit the safe handling of larger quantities of more highly radioactive materials than are currently permitted in endstations currently located on the experimental floor. The endstation is of a multiple ultra-high vacuum chamber system mounted on a low vibration (for microscopy efforts) moveable frame that can be easily transported and positioned onto several different ALS beamlines. The endstation will consist of an angle integrating electron spectrometer, "hot" preparation chamber, and a "cold" preparation-introduction chamber.

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Nuclear Science Division

Chemistry of the Heaviest Elements

Investigator(s)	Hoffman, D.C.; Gregorich, K.E.			$155,000
Phone	510-486-4474
E-mail	Hoffman@lbl.gov

The chemical properties of the heaviest elements are being investigated to explore the architecture of the periodic table of the elements at its furthest reaches and to compare their properties with those of their lighter homologs. Investigations of the dramatic changes in properties which occur in going from the actinides, which end with lawrencium (element 103), to the transactinides are especially important. Methods for studying the chemical properties of elements 102 through 106 are developed, even though some of the half-lives are only seconds and only small numbers of atoms can be produced. Chemical separations of elements 102-105 have been used to determine their most stable oxidation states in aqueous solution, thus confirming their positions in the periodic table. Both liquid-liquid extractions and isothermal gas chromatography are used to study and compare the halide complexes of elements 104 and 105 with those of their lighter homologs. The detailed studies of chemical properties of the heaviest elements have shown anomalous trends which cannot be predicted on the basis of simple extrapolations of known periodic table trends. It is important to extend studies to even heavier elements and to compare the results with predictions of fully relativistic calculations. During FY-96, our group hosted a collaboration of Norwegian, Swedish, and German scientists which successfully used the fast liquid-liquid extraction system, SISAK, in conjunction with a flowing liquid scintillation system to study the chemical properties of hahnium (105) using 1.8-second ²⁶¹Ha produced at the LBNL 88-Inch Cyclotron. Participation in an international collaboration to use the full range of automated liquid and gas-phase chemical separation systems to perform the first ever chemical studies of seaborgium (Sg, element 106) using the recently reported longer-lived isotopes of Sg is in progress.

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Chemical Science and Technology Division

Actinide Organometallic Chemistry

Investigator(s)	Burns, C.J.			$126,000
Phone	505-665-1765
E-mail	cjb@lanl.gov

These investigations seek to extend our understanding of the chemical behavior and electronic structure of complexes of the actinide elements. Synthetic studies of the nonaqueous coordination and organometallic chemistry of the actinides play a key role in improving our knowledge of redox chemistry and metal-ligand bond strengths. This type of information is critical to the development of advanced chemical processes, analytical tools, and predictive models applicable in actinide recovery, waste treatment, and environmental restoration activities. Efforts over the past year have focused on understanding factors which stabilize chemical complexes of actinides in higher oxidation states (e.g. hexavalent uranium). During the past year, we have developed much more general synthetic pathways for the introduction of imido functional groups at actinide centers, permitting the isolation of saturated alkylimido complexes. The enhanced nucleophilicity of the alkylimido derivatives can be exploited in the generation of products derived from H-H, Si-H, and C-H bond activation (including the isolation of an unusual example of an uranium metallocene which has undergone activation of a ring substituent). We have also been able to develop multi-electron transfer reactions which can either break bonds in substrates (such as the cleavage of azobenzene to generate the bisimido complex (C₅Me₅)₂U(NPh) ₂) or make bonds to generate coupled products (e.g. alkyne coupling). While the chemistry of uranium is similar in some respects to that of the Group 4 transition metals, this multi-electron transfer capability only finds precedent in the chemistry of the Group 6 metals. Current studies are aimed at identifying whether this result suggests an enhanced degree of covalency in chemical bonding in the higher valent actinide complexes.

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Chemical Science and Technology Division

Actinide Chemistry in Near-Neutral Solutions

Investigator(s)	Clark, D.L.			$139,000
Phone	505-665-4622
E-mail	dlclark@lanl.gov

The project objective is to provide fundamental physicochemical knowledge pertinent to the behavior of transuranic elements under environmental near-neutral pH conditions. Advances continue in the application of C-13 and O-17 NMR, Raman, NIR, and XAS spectroscopy towards determining the stability fields and molecular structures of actinyl (U, Np, Pu) carbonato complexes. Bulky cations (TMA, TBA) afford a relatively high solubility for Np(V) mono, bis, and tris carbonato complexes, NpO₂(CO₃)^- (I), NpO₂(CO₃)₂^3- (II), and, NpO₂(CO₃)₃^4- (III). Thermodynamic data establish the stoichiometry of I-III, NIR spectra verifies that individual solutions of I-III contain a single species, and EXAFS spectra provide structural details. II and III show hexagonal bipyramidal coordination geometries with bidentate carbonate ligands, while I shows pentagonal bipyramidal coordination. All complexes show bidentate carbonate ligation, with the remainder of equatorial sites occupied by water molecules. Axial Np=O distances are 1.85±0.02Å, while equatorial Np-O distances span 2.48 -2.53Å. Bidentate carbonate ligation is indicated by the Np--C distances of 2.93 - 2.99Å and the number of carbons is half the number of equatorial carbonate oxygens. These carbonato complexes of Np(V) have been known for over a decade, but this work is the first elucidation of the molecular structures of these environmentally important compounds. The solid-liquid equilibrium of Np(V) was studied in NaCl at 25°C and 0.01 atm CO₂. The equilibrium solids were characterized using powder X-ray diffraction, and the Np(V) solution species were characterized using NIR absorption spectroscopy. The solid phases NaNpO₂CO₃·nH₂O at [CO₃^2-] <0.001 M and Na₃NpO₂(CO₃)₂·nH₂O at [CO₃^2-] >0.001 M were found as solubility limiting solid equilibrium phases. The comparison of Np(V) solubility data in NaCl and NaClO₄ solutions indicated a stabilization of Np(V) in solution due to the interaction with chloride ions. The Pitzer approach was applied to parameterize experimental data and to predict Np(V) solubility in brine solutions.

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Chemical Science and Technology Division

Actinide Chemistry in Alkaline Radioactive Waste

Investigator(s)	Clark, D.L.; Agnew, S.F.; Neu, M.P.; Tait, C.D.; Morris, D.E.; Donohoe, R.J.; Conradson, S.D.			$250,000
Phone	505-665-4622
E-mail	dlclark@lanl.gov

The project objective is to systematically prepare and study high valent actinide complexes formed under highly alkaline conditions similar to that of aging radioactive waste tanks at Hanford, Savannah River, INEL, West Valley, and Oak Ridge. Under strongly alkaline conditions ([OH^-] = 2-14 M), actinide elements can be significantly more soluble and have unusual sorption characteristics, causing difficulty in separations and the ultimate partitioning into high level and low level waste components. Under alkaline conditions, actinide ions can form a relatively stable heptavalent state. Solids of formula MNpO₄·nH₂O (M = Cs, K, Na, Li) have been prepared and are reported to be very stable in the solid state. A few single crystal X-ray structures have been determined for salts which display the highly unusual tetragonal bipyramidal NpO₄(OH)₂^3- central core, but there are no data to support which structural motif exists in alkaline solution. This year we performed an EXAFS study of Np(VII) in alkaline solution to resolve this important issue. Alkaline Np(VII) solutions were prepared by bubbling O₃ through 2.5M NaOH containing NpO₂(OH)₂, and the resulting dark green solution characterized using Vis-NIR spectroscopy which revealed two absorption features with maxima at 410 and 625 nm consistent with those reported previously for dark green Np(VII) solutions. The EXAFS data show unequivocally that the Np(VII) species in alkaline solution must contain a trans dioxo ion (Np=O = 1.85Å), formally based on the NpO₂³⁺ central unit, which must be coordinated to five OH^- and one OH₂ ligands with Np-O distances of 2.18 and 2.42Å, respectively. This structural type has not been previously observed for Np(VII).

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Chemistry Division

Chemistry of Transuranium Elements and Compounds

Investigator(s)	Haire, R.G.; Assefa, Z.; Gibson, J.K.; Johnson, E.; Peterson, J.R.			$1,272,000
Phone	423-574-5007
E-mail	HAIRERG@ornl.gov

The program's objectives are to promote a fundamental and technological understanding of the chemistry, physics and materials science of actinide elements, compounds and alloys. The primary goal is to define and understand chemical and physical behaviors in terms of fundamental electronic interactions, thermodynamics and scientific principles. The science of these materials is advanced through systematic investigations, which establish trends and differences in behavior with changing electronic configurations. Both experimental and theoretical approaches are employed in pursuing this goal. Experimental research focuses on the vapor- and solid-state science of the actinides. Primary experimental disciplines and capabilities include: high-pressure studies; high-temperature mass spectrometry and X-ray diffraction; laser ablation mass spectrometry; thermal analyses; optical spectroscopy; and novel/microscale synthetic techniques. Selected areas of investigation are phase behaviors of metal systems; oxidation state behavior in solids and vapors; high-temperature vaporization processes and thermodynamics; vapor state cluster chemistry; and spectroscopic investigations of electronic levels and transfer processes. Theoretical and computational studies (quantum chemistry and statistical mechanics) are employed for interpretation of experimental findings, modeling and deriving scientific information via first-principle considerations.

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Controlled Clean Lab Enclosure for XAFS Studies of Radioactive and Toxic Samples on Beam Line 11 at the Stanford Synchrotron Radiation Laboratory

Investigator(s)	Hodgson, K.O.; Bienenstock, A.I.; Brown, G.E., Jr.; Carroll, S.A.; Conradson, S.D.; Edelstein, N.; Rabedeau, T.			$200,000 Equipment
Phone	415-723-9168
E-mail	hodgson@slac.stanford.edu

During the past few years, there has been increasing demand at the Stanford Synchrotron Radiation Laboratory by national laboratory and university scientists for beam time on high-flux, insertion-device beam lines to characterize the chemical forms (speciation) of radionuclides and toxic heavy metals in environmental samples. To help meet the needs in this new research area, DOE-BES-Chemical Sciences is funding a new wiggler beam line at SSRL (BL-11) devoted to molecular environmental science research. This new beam line is currently under construction and should be commissioned in early 1998. An essential component of this new environmental sciences beam line is a controlled clean laboratory that will be built around the experimental hutch. This facility is required to permit safe sample handling, temporary storage, and XAFS spectroscopy studies on environmental samples containing radionuclides, particularly transuranics, and highly toxic or carcinogenic species. This project will provide the funding to construct this controlled experimental area on BL-11. Because this will be a permanent installation, with all the necessary equipment for radiation monitoring and safe sample handling and containment, it will also permit increased numbers of radioactive and toxic samples to be studied without the time-consuming and inefficient set-up and dismantling times now required on SSRL Beam Line 4-2, where XAFS studies of samples containing these elements are typically carried out. We are currently exploring various design features for this clean lab with members of the BL-11 Advisory Committee and plan to have a detailed plan developed within the next four months. Construction of the clean lab and experimental hutch is planned in 1997. When BL-11 and the controlled clean laboratory are completed, a major new synchrotron radiation facility for XAFS studies of radioactive and toxic elements in natural samples, man-made waste forms, and simplified synthetic analog systems will be available to the growing number of environmental science users at SSRL. The results of these studies (speciation of contaminants, spatial distribution of different contaminant species, chemical and biochemical factors affecting transformations among species, and the kinetics of such transformations) will have a major impact on improving the technologies needed to address and solve contamination and waste management problems within the U.S. weapons complex and at numerous sites contaminated as a result of past and present agricultural and industrial activities, mining, and manufacturing.

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