DOI: 10.17188/1685831
title: Materials Data on Mg9Si4(HO9)2 by Materials Project

description: Mg9Si4(HO9)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are five inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to six O2- atoms to form distorted MgO6 octahedra that share corners with four MgO6 octahedra, corners with three SiO4 tetrahedra, an edgeedge with one MgO6 octahedra, and an edgeedge with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 53–64°. There are a spread of Mg–O bond distances ranging from 2.05–2.33 Å. In the second Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with eight MgO6 octahedra, corners with four SiO4 tetrahedra, edges with two MgO6 octahedra, and an edgeedge with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 51–61°. There are a spread of Mg–O bond distances ranging from 2.06–2.31 Å. In the third Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four MgO6 octahedra, corners with two SiO4 tetrahedra, edges with three MgO6 octahedra, and edges with two SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 54–64°. There are a spread of Mg–O bond distances ranging from 2.10–2.18 Å. In the fourth Mg2+ site, Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with four equivalent MgO6 octahedra, corners with two equivalent SiO4 tetrahedra, edges with four MgO6 octahedra, and edges with two equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 57–61°. There are two shorter (2.10 Å) and four longer (2.14 Å) Mg–O bond lengths. In the fifth Mg2+ site, Mg2+ is bonded in a 6-coordinate geometry to one H1+ and six O2- atoms. The Mg–H bond length is 2.21 Å. There are a spread of Mg–O bond distances ranging from 2.05–2.23 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four MgO6 octahedra and edges with two MgO6 octahedra. The corner-sharing octahedra tilt angles range from 56–61°. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six MgO6 octahedra and edges with three MgO6 octahedra. The corner-sharing octahedra tilt angles range from 56–61°. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. H1+ is bonded in a single-bond geometry to one Mg2+ and one O2- atom. The H–O bond length is 0.97 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded to three Mg2+ and one Si4+ atom to form distorted corner-sharing OMg3Si trigonal pyramids. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Mg2+ and one Si4+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to three Mg2+ and one H1+ atom. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the seventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the eighth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom. In the ninth O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Mg2+ and one Si4+ atom.