Heptairon bis(phosphate) tetrakis(hydrogenphosphate)

A new iron hydrogen phosphate, heptairon bis­(phosphate) tetrakis­(hydrogen­phosphate), Fe7(PO4)2(HPO4)4, has been prepared hydro­thermally and characterized by single‐crystal X‐ray diffraction. The compound has one Fe atom on an inversion centre and is isostructural with Mn7(PO4)2(HPO4)4 and Co7(PO4)2(HPO4)4. The structure is based on a framework of edge‐ and corner‐sharing FeO6, Fe5 and PO4 polyhedra, isotypic with that found in the mixed‐valence iron phosphate Fe7(PO4)6. The Fe atoms in the title compound are purely in the divalent state, just like the Co atoms in Co7(PO4)2(HPO4)4, the necessary charge balance being maintained by the addition of H atoms in the form of bridging Fe—OH—P groups.