Materials Data on Mg5Si2(O4F)2 by Materials Project

Abstract

Mg5F2(SiO4)2 is beta indium sulfide-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are three inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to four O2- and two equivalent F1- atoms to form MgO4F2 octahedra that share corners with six MgO4F2 octahedra, corners with two equivalent SiO4 tetrahedra, edges with three MgO4F2 octahedra, and an edgeedge with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–59°. There are a spread of Mg–O bond distances ranging from 2.01–2.19 Å. There are one shorter (2.02 Å) and one longer (2.05 Å) Mg–F bond lengths. In the second Mg2+ site, Mg2+ is bonded to five O2- and one F1- atom to form MgO5F octahedra that share corners with eight MgO6 octahedra, corners with three equivalent SiO4 tetrahedra, edges with two MgO4F2 octahedra, and an edgeedge with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–61°. There are a spread of Mg–O bond distances ranging from 2.06–2.23 Å. The Mg–F bond length is 2.06 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four equivalent MgO5F octahedra, corners with two equivalent SiO4 tetrahedra, edges with four MgO4F2 octahedra, and edges with two equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–61°. There are a spread of Mg–O bond distances ranging from 2.11–2.14 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six MgO4F2 octahedra and edges with three MgO6 octahedra. The corner-sharing octahedra tilt angles range from 56–60°. There is one shorter (1.63 Å) and three longer (1.66 Å) Si–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the third O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to three Mg2+ and one Si4+ atom. F1- is bonded in a distorted trigonal planar geometry to three Mg2+ atoms.