The solid solution K3.84Ni0.78Fe3.19(PO4)5.

The title compound, tetra-potassium tetra-[nickel(II)/iron(III)] penta-kis-(orthophosphate), K3.84Ni0.78Fe3.19(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 tetra-hedra, 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 hexa-gonally 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.