The transition metal orthophosphates Na2 M 2Fe(PO4)3 (M = Co, Ni) crystallize in an alluaudite-type structure. The chains characterizing the alluaudite structure are then built up from [M 2O10] units alternating with [FeO6] octa­hedra.

The transition metal orthophosphate Ag1.655Co1.64Fe1.36(PO4)3 crystallizes in an alluaudite-type structure. The chains characterizing the alluaudite structure are built up from edge-sharing [CoO6] and [FeO6] octa­hedra linked together by PO4 tetra­hedra. The Ag+ cations are located in two types of channels in the resulting framework.

The transition metal orthophosphate, SrCo2Fe(PO4)3, crystallizes in an alluaudite-type structure. The chains characterizing the alluaudite structure are built up from edge-sharing [CoO6] octa­hedra linked together by PO4 tetra­hedra.

Single crystals of the title compound are prepared by solid state reaction of a 1:2:1:3 molar mixture of Sr, Co, and Fe nitrates along with NH4H2PO4 (Pt crucible, 1343 K; cooling to 273 K at a rate of 5 K/h).