Materials Data on Mg5Cr(Si2O9)2 by Materials Project

Mg2CrO6Mg3Si4O12 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of two Mg2CrO6 sheets oriented in the (0, 0, 1) direction and two Mg3Si4O12 sheets oriented in the (0, 0, 1) direction. In each Mg2CrO6 sheet, there are two inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form distorted edge-sharing MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.01–2.20 Å. In the second Mg site, Mg is bonded to six O atoms to form distorted edge-sharing MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.02–2.21 Å. Cr is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Cr–O bond distances ranging from 1.69–2.11 Å. There are six inequivalent O sites. In the first O site, O is bonded in a 3-coordinate geometry to two Mg and one Cr atom. In the second O site, O is bonded in a trigonal non-coplanar geometry to two Mg and one Cr atom. In the third O site, O is bonded in a distorted trigonal non-coplanar geometry to two Mg and one Cr atom. In the fourth O site, O is bonded in a 3-coordinate geometry to two Mg and one Cr atom. In the fifth O site, O is bonded in a distorted trigonal non-coplanar geometry to two Mg and one Cr atom. In the sixth O site, O is bonded in a distorted T-shaped geometry to two Mg and one Cr atom. In each Mg3Si4O12 sheet, there are three inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with four SiO4 tetrahedra and edges with six MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.01–2.16 Å. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with four SiO4 tetrahedra and edges with six MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.01–2.16 Å. In the third Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with four SiO4 tetrahedra and edges with six MgO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.06–2.11 Å. There are four inequivalent Si sites. In the first Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with three MgO6 octahedra and corners with three equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–58°. There is one shorter (1.64 Å) and three longer (1.65 Å) Si–O bond length. In the second Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with three MgO6 octahedra and corners with three equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–58°. There is one shorter (1.64 Å) and three longer (1.65 Å) Si–O bond length. In the third Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with three MgO6 octahedra and corners with three equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–58°. There is two shorter (1.64 Å) and two longer (1.65 Å) Si–O bond length. In the fourth Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with three MgO6 octahedra and corners with three equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–59°. There is three shorter (1.64 Å) and one longer (1.65 Å) Si–O bond length. There are twelve inequivalent O sites. In the first O site, O is bonded in a trigonal non-coplanar geometry to three Mg atoms. In the second O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the third O site, O is bonded in a distorted rectangular see-saw-like geometry to three Mg and one Si atom. In the fourth O site, O is bonded in a distorted rectangular see-saw-like geometry to three Mg and one Si atom. In the fifth O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the sixth O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the seventh O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the eighth O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the ninth O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the tenth O site, O is bonded in a distorted rectangular see-saw-like geometry to three Mg and one Si atom. In the eleventh O site, O is bonded in a trigonal non-coplanar geometry to three Mg atoms. In the twelfth O site, O is bonded in a distorted rectangular see-saw-like geometry to three Mg and one Si atom.