Actinides in Solution: Complexation and Kinetics

Abstract

The solution chemistry of the actinide elements has been explored in aqueous and organic solutions. While the relative stabilities of the actinide oxidation states and the types of complexes formed with the actinide cations in these states vary between solvents, the fundamental principles governing their redox reactions and their complexation strengths are the same regardless of the solvent. This chapter focuses on aqueous actinide chemistry, reflecting the wide variety of studies on actinide reactions in aqueous solutions. However, three factors that are important for actinides in non-aqueous solvents should be noted. First, in non-aqueous solvents, the formation of neutral cation-anion ion pairs is often dominant due to the lower (as compared to water) dielectric constants of the solvents. Second, non-aqueous conditions also allow the formation of complexes between actinide cations and ligands containing soft Lewis base groups, such as sulfur. Third, non-aqueous solvents are often useful for stabilizing redox-sensitive actinide complexes, as oxidation states that are unstable in aqueous solution may be stable in non-aqueous solutions (Mikheev et al., 1977; Hulet et al., 1979).