CsFe3(PO4)3(OH2)2: a mixed-valence iron phosphate containing trimeric units of iron–oxygen polyhedra

Abstract

A mixed-valence iron phosphate, CsFe₃(PO₄)₃(OH₂)₂, has been synthesized hydrothermally and characterized by single-crystal X-Ray diffraction and Mössbauer spectroscopy. The compound crystallizes in the monoclinic space group C2/c with a= 13.435(2), b= 10.488(1), c= 9.024(2)Å, β= 108.60(1)°, U= 1205.1(3)ų and Z= 4. The structure consists of a three-dimensional framework of vertex-sharing Fe^IIIO₅ trigonal bipyramids, Fe^IIO₄(OH₂)₂ octahedra and PO₄ tetrahedra, enclosing a network of cavities, where the caesium cations reside. Mössbauer spectroscopy confirms the presence of one Fe^II and two Fe^III.