Synthesis and single crystal X-ray diffraction study of U(VI), Np(VI), and Pu(VI) perchlorate hydrates

Abstract

The compounds [AnO2(H2O)5](ClO4)2 (An = Np, Pu) and [NpO2(ClO4)2(H2O)3] were prepared as single crystals, which were studied by X-ray diffraction at 100 K. The structural type at room temperature was determined. The low-temperature modification of [UO2(H2O)5](ClO4)2 was found and structurally studied. The coordination polyhedra in [AnO2(H2O)5]2+ are weakly distorted pentagonal bipyramids with averaged interatomic distances An-O of 1.754, 1.744, and 1.732 A in the “yl” groups and of 2.415, 2.416, and 2.409 A in the equatorial planes for U, Np, and Pu, respectively. Hence, in the complex cations [AnO2(H2O)5]2+ the actinide contraction is manifested only in regular shortening of the An-O interatomic distances in the “yl” groups. The compound [NpO2(ClO4)2(H2O)3], isostructural to its known uranyl analog, appeared to be the first, proved by single crystal X-ray diffraction, example of a compound with coordination interaction between the perchlorate ion and the neptunyl(VI) cation.