Materials Data on MgCr(SiO3)2 by Materials Project
MgCr(SiO3)2 is Esseneite structured and crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with six equivalent SiO4 tetrahedra and edges with two equivalent MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.06–2.22 Å. Cr2+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are two shorter (2.07 Å) and two longer (2.20 Å) Cr–O bond lengths. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent MgO6 octahedra and corners with two equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 40–60°. There are a spread of Si–O bond distances ranging from 1.62–1.68 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Si4+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Mg2+, one Cr2+, and one Si4+ atom. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Mg2+, one Cr2+, and one Si4+ atom.