Crystal structure, charge-distribution and bond-valence-sum investigations of a new layered phosphate SrFe(HPO4)(PO4)

Abstract

The new compound SrFe(HPO4)(PO4), has been prepared using mild hydrothermal conditions under autogenous pressure and characterized by single-crystal X-ray diffraction. The crystal structure of this compound crystallizes in the triclinic system space group P-1 with Z = 2 and the cell parameters a = 5.1766 (2) Å, b = 7.1346 (2) Å, c = 8.5695 (3) Å, α = 91.093 (2)°, β = 91.029 (2)°, γ = 90.313 (2)°, V = 316.36 (2) Å3. The structure exhibits a layered framework which could be described as a stacking [Fe(HPO4)(PO4)]∞2− layers of corner sharing FeO6 octahedra and the bridging PO4/PO3(OH) tetrahedra along the [010] direction. Such hetero-polyhedral arrangement gives a rise to a strong O—H···O hydrogen bonds into the intra-layers region. Adjacent layers are held to each other through the Sr2+ cations located in the resulting corrugated interstitial space. The validation of the proposed structural model is supported by means bond-valence-sum (BVS) and charge-distribution (CHARDI) methods.