Sodium pentapotassium pentanickel tetra(diphosphate), NaK5Ni5(P2O7)4

Abstract

The structure of the title compound, NaK5Ni5(P2O7)4, is characterized by the presence of two crystallographically independent P2O7 groups with different conformations. The conformation of the first P2O7 group is eclipsed, whereas that of the second is staggered. All atoms are in general positions except for two nickel and one potassium ions which lie on symmetry centers. Moreover, the structure exhibits disorder of the cationic sites with one general position fully occupied equally by Na+ and Ni2+ cations. This mixed site is surrounded by five O atoms forming a square-based pyramid. The crystal structure consists of edge-sharing [NiO6] octahedra forming infinite zigzag chains [Ni3O14] running parallel to [100]. Adjacent chains are connected through apices to P2O7 groups and to another [NiO6] or to a [KO6] octahedron. The resulting three-dimensional framework presents intersecting tunnels running along the [010] and [001] directions in which the seven- and nine-coordinated potassium cations are located. The crystal structure of this new phosphate represents a new structural type.