Structural Characterization of a Plutonium Sequestering Agent Complex by Synchrotron X-Ray Diffraction
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Structural Characterization of a Plutonium Sequestering Agent Complex by Synchrotron X-Ray Diffraction A. E. V. Gorden1,2, G. Szigethy1,3, D. K. Shuh3, B. E. F. Tiedemann1, J. Xu1, and K. N. Raymond1,3 1 Dept. of Chemistry, Univ. of California Berkeley, Berkeley, CA, 94720 2 Dept. of Chemistry and Biochemistry, Auburn University, Auburn, AL, 36849 3 Lawrence Berkeley National Laboratory, Berkeley, CA, 94720
ABSTRACT New ligands and materials are required that can coordinate, sense, and purify actinides for selective extraction and reduction of toxic, radioactive wastes from the mining and purification of actinides. The similarities in the chemical, biological transport, and distribution properties of Fe(III) and Pu(IV) inspired a biomimetic approach to the development of sequestering agents for actinides. A detailed evaluation of the structure and bonding of actinide coordinating ligands like these is important for the design of new selective ligand systems. Knowing the difficulty with working with the crystals resulting from these ligand systems and safe handling considerations for working with Pu, procedures were developed that utilize the Advanced Light Source of Lawrence Berkeley National Laboratory to determine the solid-state structures of Pu complexes by X-ray diffraction. INTRODUCTION A resurgence of interest in actinide coordination chemistry has been inspired in part by environmental issues surrounding the long-term storage of radioactive waste materials and remediation of radioactive wastes toward more environmentally friendly production of electricity from nuclear fuels [1-3]. The similarities in the chemical, biological transport, and distribution properties of Fe(III) and Pu(IV) inspired the development of sequestering agents for actinides based on hydroxypyridonate (HOPO) chelating units found in naturally occurring Fe(III) sequestering agents. Hydroxypyridonate ligands have been found to be excellent systems for decorporation in studies on mice,[4] and have been investigated in systems for actinide selective extraction [5-6]. This project has since broadened to include other related coordinating compounds that might be found in a high humic or fertile soil including carbohydrates, carboxylic acids, and other natural products. In order to further study these types of systems, it is clear that it would be most desirable to study the coordination chemistry of these ligand systems with the targeted actinides. A detailed assessment of the structures of the actinide complexes formed is particularly important if new synthetic chelating ligands are to be designed for the selective coordination of actinide ions. This program of research incorporates structural inorganic chemistry with a variety of analytical methods for the characterization of metal complexes of actinides and lanthanides as model systems. This is particularly important, given the relatively small amount of available research on these materials. For example, less than 25 plutonium complexes have been characterized by single-crys
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