Crystal structure of calcium dinickel(II) iron(III) tris-(orthophosphate): CaNi2Fe(PO4)3.

The title compound, CaNi2Fe(PO4)3, was synthesized by solid-state reactions. Its structure is closely related to that of α-CrPO4 in the space group Imma. Except for two O atoms in general positions, all atoms are located in special positions. The three-dimensional framework is built up from two types of sheets extending parallel to (100). The first sheet is made up from two edge-sharing [NiO6] octa-hedra, leading to the formation of [Ni2O10] double octa-hedra that are connected to two PO4 tetra-hedra through a common edge and corners. The second sheet results from rows of corner-sharing [FeO6] octa-hedra and PO4 tetra-hedra forming an infinite linear chain. These layers are linked together through common corners of PO4 tetra-hedra and [FeO6] octa-hedra, resulting in an open three-dimensional framework that delimits two types of channels parallel to [100] and [010] in which the eightfold-coordinated CaII cations are located.