A new iron oxophosphate SrFe3(PO4)3O with chain-like structure

A new strontium iron oxophosphate SrFe₃(PO₄)₃O was synthesized by the solid state method and its structure was studied by single-crystal X-ray and electron diffraction, high-resolution electron microscopy, Mössbauer and IR spectroscopy. The compound crystallizes in a monoclinic system (space group P2₁/m) with unit-cell parameters: a = 7.5395(7), b = 6.3476(7) c = 10.3161(13) Å, β = 99.740(9)°. The structure of SrFe₃(PO₄)₃O represents a new structural type and is made up of isolated PO₄ tetrahedra and FeO_n polyhedra connected via common vertices and edges to form a 3D framework. Iron cations occupy three crystallographically independent sites with different oxygen environment: Fe1 and Fe2 occupy two octahedral sites, and Fe3 is five-coordinated. Two particularities of this structure are remarkably mentioned: the isolated {FeO₆}_n octahedral chains along the b direction and the five coordinated environment for the Fe3 position. Mössbauer spectroscopy confirmed the presence of only high-spin Fe³⁺ cations in two types of coordination environment. The IR-data show the presence of only PO₄³⁻ groups.