DOI: 10.17188/1318579
title: Materials Data on MgCr4O8 by Materials Project

description: MgCr4O8 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. Mg2+ is bonded to five O2- atoms to form MgO5 square pyramids that share corners with six CrO6 octahedra, edges with three CrO6 octahedra, edges with two equivalent MgO5 square pyramids, and a faceface with one CrO6 octahedra. The corner-sharing octahedra tilt angles range from 5–56°. There are a spread of Mg–O bond distances ranging from 2.07–2.10 Å. There are four inequivalent Cr+3.50+ sites. In the first Cr+3.50+ site, Cr+3.50+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with four CrO6 octahedra, edges with four CrO6 octahedra, and edges with two equivalent MgO5 square pyramids. The corner-sharing octahedra tilt angles range from 48–52°. There are a spread of Cr–O bond distances ranging from 1.92–2.16 Å. In the second Cr+3.50+ site, Cr+3.50+ is bonded to six O2- atoms to form distorted CrO6 octahedra that share corners with four CrO6 octahedra, corners with two equivalent MgO5 square pyramids, edges with four CrO6 octahedra, and a faceface with one MgO5 square pyramid. The corner-sharing octahedra tilt angles range from 48–55°. There are a spread of Cr–O bond distances ranging from 1.88–2.18 Å. In the third Cr+3.50+ site, Cr+3.50+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with four CrO6 octahedra, corners with two equivalent MgO5 square pyramids, and edges with four CrO6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are a spread of Cr–O bond distances ranging from 1.92–2.04 Å. In the fourth Cr+3.50+ site, Cr+3.50+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with four CrO6 octahedra, corners with two equivalent MgO5 square pyramids, edges with four CrO6 octahedra, and an edgeedge with one MgO5 square pyramid. The corner-sharing octahedra tilt angles range from 52–55°. There are a spread of Cr–O bond distances ranging from 1.92–2.11 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to three Cr+3.50+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Cr+3.50+ atoms. In the third O2- site, O2- is bonded in a trigonal planar geometry to three Cr+3.50+ atoms. In the fourth O2- site, O2- is bonded to one Mg2+ and three Cr+3.50+ atoms to form OMgCr3 trigonal pyramids that share corners with two equivalent OMgCr3 trigonal pyramids, edges with two equivalent OMg2Cr3 square pyramids, and edges with two equivalent OMg2Cr3 trigonal bipyramids. In the fifth O2- site, O2- is bonded in a trigonal non-coplanar geometry to three Cr+3.50+ atoms. In the sixth O2- site, O2- is bonded to two equivalent Mg2+ and three Cr+3.50+ atoms to form distorted OMg2Cr3 trigonal bipyramids that share corners with two equivalent OMg2Cr3 square pyramids, an edgeedge with one OMg2Cr3 square pyramid, edges with two equivalent OMg2Cr3 trigonal bipyramids, and edges with two equivalent OMgCr3 trigonal pyramids. In the seventh O2- site, O2- is bonded to two equivalent Mg2+ and three Cr+3.50+ atoms to form OMg2Cr3 square pyramids that share corners with two equivalent OMg2Cr3 trigonal bipyramids, edges with two equivalent OMg2Cr3 square pyramids, an edgeedge with one OMg2Cr3 trigonal bipyramid, and edges with two equivalent OMgCr3 trigonal pyramids. In the eighth O2- site, O2- is bonded in a trigonal non-coplanar geometry to three Cr+3.50+ atoms.