Heptairon bis(phosphate) tetrakis(hydrogenphosphate).

A new iron hydrogen phosphate, heptairon bis(phosphate) tetrakis(hydrogenphosphate), Fe(7)(PO(4))(2)(HPO(4))(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 Mn(7)(PO(4))(2)(HPO(4))(4) and Co(7)(PO(4))(2)(HPO(4))(4). The structure is based on a framework of edge- and corner-sharing FeO(6), Fe(5) and PO(4) polyhedra, isotypic with that found in the mixed-valence iron phosphate Fe(7)(PO(4))(6). The Fe atoms in the title compound are purely in the divalent state, just like the Co atoms in Co(7)(PO(4))(2)(HPO(4))(4), the necessary charge balance being maintained by the addition of H atoms in the form of bridging Fe-OH-P groups.