Complexes of An(VI) with Cyclobutanecarboxylic Acid Anions and Outer-Sphere Alkali Metal Cations

Abstract

New complexes of hexavalent actinides with cyclobutanecarboxylic acid (Hcbc) anions, Na4[NpO2· (cbc)3]4·H2O (I), K[NpO2(cbc)3] (II), Cs[NpO2(cbc)3] (III), and Cs[PuO2(cbc)3] (IV), cbc = C4H7(COO)–, were synthesized and studied by single crystal X-ray diffraction. The structures of I–IV are based on the anionic complexes [AnO2(cbc)3]– surrounded by alkali metal cations. The AnO 2 2+ cation in the anionic complex is bonded with three chelating C4H7COO– anions, and the coordination polyhedron (CP) of An is a hexagonal bipyramid with the O atoms of the AnO 2 2+ cations in apical positions. The coordination number (CN) of the alkali metal cations in the structures of II–IV is the same and equal to 6; the coordination surrounding of the K+ and Cs+ cations is constituted by the O atoms of six C4H7COO– anions. The crystal structures of II–IV are examples of cubic 3-connected networks (10,3) built of alkali metal and actinide cations. In the structure of I, there are four kinds of crystallographically different NpO 2 2+ and Na+ cations. The coordination surrounding of the NpO 2 2+ cations differs only in the conformational characteristics of the C4H7COO– ligands. Four independent Na+ cations differ from each other in the structure of the coordination surrounding. The CPs of the Na(1) and Na(4) atoms can be described as distorted octahedra (CN 6); that of Na(3), as a trigonal prism (CN 6); and that of Na(2), as a tetragonal pyramid (CN 5) with one of the basal vertices occupied by the Ow(1) atom of a water molecule. In the structure of I, the configuration of the network formed by the Na and Np cations differs from the cubic 3-connected network found in the structures of II–IV.