Hydrothermal synthesis and structural characterisation of SrFe3(PO4)3(HPO4), an iron(III) phosphate containing FeO5 trigonal bipyramids and dimers of face-sharing FeO6 octahedra

Abstract

A new iron(III) phosphate, SrFe₃(PO₄)₃(HPO₄), has been synthesised hydrothermally and characterised by single-crystal X-ray diffraction and Mössbauer spectroscopy. The compound crystallises in the monoclinic space group P2₁/c, with a= 8.476(2), b= 7.298(1), c= 19.501(3)Å, β= 94.96(2)°, and Z= 4. The structure consists of channels parallel to the a axis where the Sr atoms are located. The framwork is composed of dimers of face-sharing FeO₆ octahedra, discrete FeO₅ trigonal bipyramids, phosphate tetrahedra, and hydrogenphosphate groups. Room-temperature Mössbauer spectroscopy confirms the presence of high-spin Fe^III.