Synthesis and X-ray diffraction study of monohydrates of rubidium and cesium salts of Np(VII) and Pu(VII)

Abstract

The compounds Rb3[AnO4(OH)2]·H2O and Cs3[AnO4(OH)2]·H2O, where An = Np or Pu, were prepared as single crystals by crystallization from alkaline solutions of Np(VII) and Pu(VII) in the course of their drying at 70–75°C. The crystals were subjected to X-ray diffraction analysis. All the compounds are isostructural and contain An atoms in the form of [AnO4(OH)2]3− anions in which the oxygen surrounding of the An atoms is a slightly distorted tetragonal bipyramid. The averaged An-O distances in the equatorial planes of the bipyramids vary insignificantly (within 1.884–1.892 A), tending to slightly decrease in going from Np to Pu. This trend is more pronounced for averaged An-OH distances, which vary in the range 2.328–2.368 A. That is, as in the case of the other previously studied An(VII) compounds, the actinide contraction is mainly manifested in shortening of the An-OH distances. One of the features of Rb3[AnO4(OH)2]·H2O and Cs3[AnO4(OH)2]·H2O structures, as compared with the trihydrates, is the lack of the symmetry center in [AnO4(OH)2]3− anions.