Synthesis and crystal structure of cesium actinide(VI) tricarbonate complexes Cs4AnO2(CO3)3·6H2O, An(VI) = U, Np, Pu

Abstract

Tricarbonate complexes of hexavalent U, Np, and Pu with outer-sphere cesium cations, Cs4AnO2·(CO3)3·6H2O, were synthesized and studied by single crystal X-ray diffraction analysis. Crystals of Cs4AnO2·(CO3)3·6H2O consist of [AnO2(CO3)3]4– complex anions and hydrated Cs+ cations. The coordination polyhedron (CP) of An(VI) atoms is a distorted hexagonal bipyramid with three CO32– anions arranged in the equatorial plane. Four independent Cs+ cations have the coordination surrounding in the form of 11-, 10-, and 9-vertex polyhedra formed by the O atoms of CO32– anions, AnO22+ cations, and water molecules. Six crystallographically independent water molecules in the structure of Cs4AnO2(CO3)3·6H2O form a three-dimensional system of hydrogen bonds in which the O atoms of carbonate ions and water molecules act as proton acceptors. The “yl” oxygen atoms of AnO22+ cations are not involved in hydrogen bonding. The lengths of the An–Ocarb bonds in the equator of the U, Np, and Pu hexagonal bipyramids are noticeably influenced by incorporation of the O atoms of the CO32– anions in the coordination polyhedra of Cs+ ions and by involvement of these atoms in hydrogen bonding.