Complexation of hexavalent U, Np, and Pu with cyclopropanecarboxylate anions. Crystal structure of the uranyl complexes {[UO2(bipy)(cpc)]2O2} and [UO2(cpc)2(H2O)2] (bipy = 2,2′-Bipyridine, cpc− = cyclopropanecarboxylate anion)

Abstract

The complexation of hexavalent U, Np, and Pu with cyclopropanecarboxylate anions, cpc−, in aqueous solutions was studied. The stepwise concentration stability constants of the complexes PuO2(cpc)i2−i (i = 1, 2, 3) are as follows: logK1,2,3 = 2.63 ± 0.20, 1.61 ± 0.20, 1.43 ± 0.20, respectively; the overall concentration stability constant of the complex PuO2(cpc)3− is logβ3 = 5.67 ± 0.60. The complexing properties of the cpc− anion are very close to those of butyrate and isobutyrate anions. Two crystalline uranyl compounds were synthesized: {[UO2(bipy)(cpc)]2O2} (bipy = 2,2′-bipyridine) and [UO2(cpc)2(H2O)2]. The specific feature of the first complex is that it contains peroxide ion. Its appearance may be due to the formation of the cationic moiety via hydrolytic uranyl dimer. The second compound forms a 3D structure, with the complexes linked via hydrogen bonds.