Solution phase coordination chemistry of trivalent lanthanide and actinide cations with bis(2,4,4-trimethylpentyl)dithiophosphinic acid

The structure and stoichiometry of the complexes between trivalent lanthanide (Nd³⁺ and Sm³⁺) and actinide (Am³⁺ and Cm³⁺) cations and bis(2,4,4-trimethylpentyl)dithiophosphinic acid have been studied in various organic diluents. The coordination numbers and metal-ligand bond distances are the same for the lanthanide and actinide complexes despite the great selectivity of this ligand for the trivalent actinides. When the aggregation of the extractant in the organic phase is taken into account, the data from liquid-liquid extraction experiments, small-angle neutron scattering, visible absorption spectroscopy, and the extended X-ray absorption fine structure all support the presence of 1:3 metal:ligand complexes in the organic phase. The cations studied appear to be small enough relative to the steric constraints of the ligands that 1:4 metal:ligand complexes are not stable. (author)