Plutonium (Ⅳ) Complexes of Mixed Pyridine N-Oxide and Phosphinoxide f-Element Extractants

摘要

Analytical and bulk scale separation and processing of aqueous acidic solutions containing f-element ions are regularly accomplished using liquid-liquid extraction (LLE) methods that employ a neutral organic donor ligand dissolved in an organic phase. Several monofunctional ligands have been used as LLE reagents, but all display one or more deficiencies due to the chemical similarity of the trivalent lanthanides (Ln) to the trivalent actindes (An). Because the trivalent 4f and 5f ions have identical charges, chemical separation agents for these two groups need to differentiate among these hard cations based on their size or chemical bonding preferences. This task is not easy because, as a consequence of the lanthanide and actinide contractions, the Ln and An fission products that need to be separated have similar ionic radii. In order to develop new ligands for the separation process, we must have a fundamental understanding of how these separation agents interact with both Ln and An ions on a molecular level. We have prepared and are studying derivatives of the mixed pyridine N-oxide and phosphinoxide ligand family shown in Figure 1. These compounds have been examined as LLE reagents in chloroform, arene, and alkane solvents, and they show favorable extraction performance for Ln(Ⅲ) and Am(Ⅲ) ions from strong HCl and HNO_3 solutions. The coordination ability of 2,6-bis[(diphenylphosphino)-methyl]benzene P,P'-dioxide (POPO) to Ln(Ⅲ) ions has also been tested. Here 2:1 complexes are isolated, with POPO acting as a bidentate ligand. The extraction performance of POPO has not yet been characterized; however, it is expected to be a more weakly coordinating ligand compared to NOPO and NOPOPO given the absence of the N-oxide donor group.