Actinide cation-cation complexes

摘要

The +5 oxidation state of U, Np, Pu, and Am is a linear dioxo cation (AnO(sub 2)(sup +)) with a formal charge of +1. These cations form complexes with a variety of other cations, including actinide cations. Other oxidation states of actinides do not form these cation-cation complexes with any cation other than AnO(sub 2)(sup +); therefore, cation-cation complexes indicate something unique about AnO(sub 2)(sup +) cations compared to actinide cations in general. The first cation-cation complex, NpO(sub 2)(sup +)(center dot)UO(sub 2)(sup 2+), was reported by Sullivan, Hindman, and Zielen in 1961. Of the four actinides that form AnO(sub 2)(sup +) species, the cation-cation complexes of NpO(sub 2)(sup +) have been studied most extensively while the other actinides have not. The only PuO(sub 2)(sup +) cation-cation complexes that have been studied are with Fe(sup 3+) and Cr(sup 3+) and neither one has had its equilibrium constant measured. Actinides have small molar absorptivities and cation-cation complexes have small equilibrium constants; therefore, to overcome these obstacles a sensitive technique is required. Spectroscopic techniques are used most often to study cation-cation complexes. Laser-Induced Photacoustic Spectroscopy equilibrium constants for the complexes NpO(sub 2)(sup +)(center dot)UO(sub 2)(sup 2+), NpO(sub 2)(sup +)(center dot)Th(sup 4+), PuO(sub 2)(sup +)(center dot)UO(sub 2)(sup 2+), and PuO(sub 2)(sup +)(center dot)Th(sup 4+) at an ionic strength of 6 M using LIPAS are 2.4 (plus minus) 0.2, 1.8 (plus minus) 0.9, 2.2 (plus minus) 1.5, and (approx)0.8 M(sup (minus)1).