Cation-cation interaction in mixed-valent An(IV)/Np(V) tribromoacetates [An(NpO2)(H2O)3(CBr3COO)5]·CBr3COOH·nH2O, An = Th(IV), Np(IV)

Abstract

The structure of new mixed-valent An(IV)/Np(V) compounds [An(NpO2)(H2O)3(CBr3COO)5]·CBr3COOH·nH2O, where An(IV) = Th and Np, was studied. Two independent Np(V) atoms have the coordination surrounding in the form of pentagonal bipyramids with the O atoms of NpO 2 + dioxocations in apical positions; the equatorial planes of the bipyramids are constituted by the O atoms of five CBr3COO− ions. Two independent An(IV) atoms have the oxygen surrounding in the form of distorted tricapped trigonal prisms (CN = 9) constituted by the O atoms of four CBr3COO− ions, two NpO 2 + cations, and three water molecules. Eight of ten independent CBr3COO− anions link the An4+ and NpO 2 + cations in the bidentate bridging fashion into electrically neutral chains [An(NpO2)(H2O)3(CBr3COO)5]n, and two CBr3COO− anions interact with two independent NpO 2 + dioxocations in the monodentate fashion. CBr3COOH and water molecules are located between the layers. In the [An(NpO2)(H2O)3(CBr3COO)5]n chains, NpO 2 + cations alternate with An4+ cations, and mixed-valent An(IV)/Np(V) cation-cation interaction arises, in which each NpO 2 + cation acts as a bidentate ligand and An4+ acts as coordination center for two dioxocations. [Th(NpO2)(H2O)3(CBr3COO)5]·CBr3COOH·2H2O is the first example of a Th(IV) compound in which cation-cation bonds with the NpO 2 + ions are present.