Cation-cation interactions in uranyl and neptunyl compounds

NUCL 36

Peter C. Burns, pburns@nd.edu and Tori Z. Forbes, tziemann@nd.edu. Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556
In a 1961 J.C. Sullivan reported “Three separate types of measurements are consistent with the concept of specific interactions between the Np(V) and uranyl ions in acid solution. No evidence has been obtained for the participation of anions in this complex.” Thus, the study of actinyl cation-cation interactions (CCI) was born. In a CCI an O atom of one actinyl ion coordinates a second actinyl ion as an equatorial vertex of a bipyramid. In uranyl ions, the U(VI)-O bond is strong enough that the bonding requirements of the uranyl O atoms are nearly met, and CCIs give a small degree of overbonding at the shared O atom. As such, CCIs occur in only about 2% of uranyl structures. Np(V)-O bonds within the neptunyl ion are somewhat weaker, favoring CCIs that occur in 50% of structures. Recent studies have revealed novel linkages, such as bifurcated CCIs, and new topological arrangements facilitated by CCIs.