DOE OSTI2020
MgCoO2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to five O2- atoms to form MgO5 trigonal bipyramids that share corners with four MgO4 tetrahedra, corners with two equivalent CoO5 trigonal bipyramids, edges with two equivalent MgO5 trigonal bipyramids, and a faceface with one CoO5 trigonal bipyramid. There are a spread of Mg–O bond distances ranging from 2.05–2.13 Å. In the second Mg2+ site, Mg2+ is bonded to five O2- atoms to form MgO5 trigonal bipyramids that share corners with four MgO4 tetrahedra, corners with two equivalent CoO5 trigonal bipyramids, edges with two equivalent MgO5 trigonal bipyramids, and a faceface with one CoO5 trigonal bipyramid. There are a spread of Mg–O bond distances ranging from 2.05–2.13 Å. In the third Mg2+ site, Mg2+ is bonded to four O2- atoms to form MgO4 tetrahedra that share corners with two equivalent MgO4 tetrahedra, corners with four MgO5 trigonal bipyramids, corners with four CoO5 trigonal bipyramids, and an edgeedge with one CoO5 trigonal bipyramid. There are a spread of Mg–O bond distances ranging from 1.96–2.00 Å. In the fourth Mg2+ site, Mg2+ is bonded to four O2- atoms to form MgO4 tetrahedra that share corners with two equivalent MgO4 tetrahedra, corners with four MgO5 trigonal bipyramids, corners with four CoO5 trigonal bipyramids, and an edgeedge with one CoO5 trigonal bipyramid. There are a spread of Mg–O bond distances ranging from 1.96–2.00 Å. There are four inequivalent Co2+ sites. In the first Co2+ site, Co2+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Co–O bond distances ranging from 1.94–2.14 Å. In the second Co2+ site, Co2+ is bonded to five O2- atoms to form distorted CoO5 trigonal bipyramids that share corners with four MgO4 tetrahedra, corners with two equivalent MgO5 trigonal bipyramids, an edgeedge with one MgO4 tetrahedra, edges with two equivalent CoO5 trigonal bipyramids, and a faceface with one MgO5 trigonal bipyramid. There are a spread of Co–O bond distances ranging from 2.04–2.32 Å. In the third Co2+ site, Co2+ is bonded to five O2- atoms to form distorted CoO5 trigonal bipyramids that share corners with four MgO4 tetrahedra, corners with two equivalent MgO5 trigonal bipyramids, an edgeedge with one MgO4 tetrahedra, edges with two equivalent CoO5 trigonal bipyramids, and a faceface with one MgO5 trigonal bipyramid. There are a spread of Co–O bond distances ranging from 2.03–2.31 Å. In the fourth Co2+ site, Co2+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Co–O bond distances ranging from 1.94–2.13 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to one Mg2+ and three Co2+ atoms to form distorted OMgCo3 tetrahedra that share corners with two equivalent OMgCo3 tetrahedra, corners with four OMg3Co2 trigonal bipyramids, and an edgeedge with one OMg3Co2 trigonal bipyramid. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to two equivalent Mg2+ and two equivalent Co2+ atoms. In the third O2- site, O2- is bonded in a rectangular see-saw-like geometry to two equivalent Mg2+ and two equivalent Co2+ atoms. In the fourth O2- site, O2- is bonded to one Mg2+ and three Co2+ atoms to form distorted OMgCo3 tetrahedra that share corners with two equivalent OMgCo3 tetrahedra, corners with four OMg3Co2 trigonal bipyramids, and an edgeedge with one OMg3Co2 trigonal bipyramid. In the fifth O2- site, O2- is bonded to three Mg2+ and two equivalent Co2+ atoms to form distorted OMg3Co2 trigonal bipyramids that share corners with four OMgCo3 tetrahedra, an edgeedge with one OMgCo3 tetrahedra, and edges with two equivalent OMg3Co2 trigonal bipyramids. In the sixth O2- site, O2- is bonded in a 5-coordinate geometry to three Mg2+ and two equivalent Co2+ atoms. In the seventh O2- site, O2- is bonded to three Mg2+ and two equivalent Co2+ atoms to form distorted OMg3Co2 trigonal bipyramids that share corners with four OMgCo3 tetrahedra, an edgeedge with one OMgCo3 tetrahedra, and edges with two equivalent OMg3Co2 trigonal bipyramids. In the eighth O2- site, O2- is bonded in a 5-coordinate geometry to three Mg2+ and two equivalent Co2+ atoms.