The solid solution K_3.84Ni_0.78Fe_3.19(PO₄)₅

The title compound, tetra­potassium tetra­[nickel(II)/iron(III)] penta­kis­(orthophosphate), K_3.84Ni_0.78Fe_3.19(PO₄)₅, has been obtained from a flux. The structure is isotypic with that of K₄MgFe₃(PO₄)₅. The three-dimensional framework is built up from (Ni/Fe)O₅ trigonal bipyramids with a mixed Fe:Ni occupancy of 0.799 (8):0.196 (10) and isolated PO₄ tetra­hedra, one of which is on a general position and one of which has -4.. site symmetry. Two K⁺ cations are statistically occupied and are distributed over two positions in hexa­gonally shaped channels that run parallel to [001]. One K⁺ cation [occupancy 0.73 (3)] is surrounded by nine O atoms, while the other K⁺ cation [occupancy 0.23 (3)] is surrounded by eight O atoms.