Department of Chemistry

Research in Actinide Chemistry

Investigator(s)	Choppin, G.R.			$123,000
Phone	904-644-3875
E-mail	choppin@chem.fsu.edu

This research emphasizes the basic studies of the behavior in solution of the actinide elements and of the chemically related lanthanide elements. The systems are chosen for investigation because the data can provide increased understanding of the principles governing the chemical behavior of the f-elements with a variety of complexing ligands, both organic and inorganic. The data may also be of direct value for modeling calculations of the behavior of actinides in environmental and waste repository systems or in improved separation schemes of these elements. Emphasis continues on the thermodynamic, kinetic, and spectroscopic (absorption and luminescence) studies of the complexation and redox reaction of the actinides. A major environmental ligand studied is humic acid to which binding of actinides in the III, IV, V, and VI states is very rapid while dissociation is much slower. Binding constants and kinetics of actinide complexation to humics for different sized fractions are being investigated by several radiotracer and spectroscopic techniques. A study of actinide complexation thermodynamics by potentiometry and calorimetry at 5, 25, 45 and 70°C. Hydrolysis of AnO₂⁺ at these temperatures in different electrolytes has been measured. Actinide binding to large, soluble anionic polyoxometallates (e.g., H₂P₂W₁₂O_48-12) is being investigated as such anions may serve as a model for clay and colloid systems. Several ligands have been synthesized and are being studied by potentiometry, calorimetry, fluorescence, NMR, raman, IR, and visible spectroscopies to evaluate their value in actinide separations.

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Department of Chemistry

Preorganized and Immobilized Ligands for Metal Ion Separations

Investigator(s)	Paine, R.T.			$106,000
Phone	505-277-1661
E-mail	rtpaine@unm.edu

The objectives of this project are to (1) design and synthesize new families of organic ligands capable of selective chelation of d- and f- block metal ions present in nuclear and industrial waste streams, (2) study the structural details of the ligand/metal complexes formed in order to improve the design and synthesis of chelators, and (3) prepare solid phase, immobilized chelators suitable for practical applications in the separations field. At the present time two classes of chelate systems are under examination: multidentate phosphonopyridine N-oxides and polyaminophosphonates. In the former group, aqueous soluble and organic solvent soluble ligands have been prepared and metal coordination chemistry has revealed key features that control metal ion selectivity. Radiochemical extraction studies have shown that these ligands are highly selective and powerful chelators for actinide (III) ions. In the case of polyaminophosphonates, water soluble reagents have been generated and the small molecule ligand properties are being used to devise approaches for the synthesis of cluster or dendritic polyaminphosphonates for colloid separations.

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Department of Chemistry

The Electronic Structure of Heavy-Element Complexes

Investigator(s)	Bursten, B. E.			$69,332
Phone	614-292-1866
E-mail	bursten.1@osu.edu

This project focuses on the use of advanced theoretical methods to calculate the electronic structure of organoactinide and related coordination complexes. The principal methodologies currently employed are the fully relativistic discrete variational X (DV-X) method, analytical-basis-set density functional methods with relativistic effective core potentials, and ab initio methods. A number of interesting new results have resulted from these calculations in the past year. First, we have generated relativistic effective core potentials for trans-actinide elements through Element 118. We have used these potentials to initiate electronic structural studies of molecules of these elements. We are also continuing our studies of the structure, bonding, and reactivity of actinide-containing molecules, particularly organometallics. Systems currently under investigation include an extensive series of sandwich compounds of the type (ⁿ--C_nH_n)₂An (An = Th, Pa, U, Np, Pu, Am; n = 6, 7, 8). We have also expanded our studies of organoactinide chemistry by examining those factors that lead to linear and bent AnL₂ moieties. These studies encompass new and exciting results by experimentalists on systems such as (⁵-C₅Me₅)₂U(NR)₂. Our results to date are consistent with the interplay of electronic effects involving both 5f and 6d orbitals of the actinide elements in determining the geometries and reactivities of these molecules.

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