Interaction of U(VI), Np(VI), Pu(VI), and Np(V) with benzenetricarboxylic acids: Complexation in aqueous solutions, synthesis, and crystal structure of uranyl complexes [UO2(H2O)2{C6H3(COO)2(COOH)}]2·2H2O and [(UO2)3(H2O)4{C6H3(COO)3}2

Abstract

The complexation of U(VI), Np(VI), and Pu(VI) and of Np(V) with 1,2,3- and 1,2,4-benzenetricarboxylic acids (BTC) in aqueous solutions was studied in wide ranges of pH and actinyl ion concentrations. The compositions of the forming hexavalent actinide complexes were determined. Their apparent stability constants β1′ depend on pH of the solution: in the pH range 2–4, logβ1′ from 2 to 4 for the complexes of U(VI), Np(VI), and Pu(VI) with 1,2,3-BTC and from 1.5 to 3.5 for the complexes with 1,2,4-BTC. For Np(V), the β1′ values are close with both acids, and at equal pH values the Np(V) complexes are less stable than the An(VI) complexes (An = U, Np, Pu). With an increase in pH from ∼3 to 6.2–6.9, logβ1′ of the Np(V) complexes increases approximately from 0.5 to 3. Solid U(VI) complexes with 1,2,3- and 1,2,4-benzenetricarboxylic acids were synthesized by the hydrothermal method, their crystal structure was determined, and the IR spectra were examined.