DOI: 10.17188/1318570
title: Materials Data on Mg(NiO2)4 by Materials Project

description: Mg(NiO2)4 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 NiO6 octahedra, edges with three NiO6 octahedra, edges with two equivalent MgO5 square pyramids, and a faceface with one NiO6 octahedra. The corner-sharing octahedra tilt angles range from 10–55°. There are a spread of Mg–O bond distances ranging from 2.04–2.16 Å. There are four inequivalent Ni+3.50+ sites. In the first Ni+3.50+ site, Ni+3.50+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with four NiO6 octahedra, edges with four NiO6 octahedra, and edges with two equivalent MgO5 square pyramids. The corner-sharing octahedra tilt angles range from 50–55°. There are a spread of Ni–O bond distances ranging from 1.88–1.97 Å. In the second Ni+3.50+ site, Ni+3.50+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with four NiO6 octahedra, corners with two equivalent MgO5 square pyramids, edges with four NiO6 octahedra, and a faceface with one MgO5 square pyramid. The corner-sharing octahedra tilt angles range from 50–56°. There are a spread of Ni–O bond distances ranging from 1.90–2.09 Å. In the third Ni+3.50+ site, Ni+3.50+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with four NiO6 octahedra, corners with two equivalent MgO5 square pyramids, and edges with four NiO6 octahedra. The corner-sharing octahedra tilt angles range from 51–55°. There are a spread of Ni–O bond distances ranging from 1.85–1.93 Å. In the fourth Ni+3.50+ site, Ni+3.50+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with four NiO6 octahedra, corners with two equivalent MgO5 square pyramids, edges with four NiO6 octahedra, and an edgeedge with one MgO5 square pyramid. The corner-sharing octahedra tilt angles range from 51–56°. There are a spread of Ni–O bond distances ranging from 1.87–2.05 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ni+3.50+ atoms. In the second O2- site, O2- is bonded in a trigonal planar geometry to three Ni+3.50+ atoms. In the third O2- site, O2- is bonded in a trigonal planar geometry to three Ni+3.50+ atoms. In the fourth O2- site, O2- is bonded to one Mg2+ and three Ni+3.50+ atoms to form distorted OMgNi3 trigonal pyramids that share corners with two equivalent OMgNi3 trigonal pyramids, edges with two equivalent OMg2Ni3 square pyramids, and edges with two equivalent OMg2Ni3 trigonal bipyramids. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to three Ni+3.50+ atoms. In the sixth O2- site, O2- is bonded to two equivalent Mg2+ and three Ni+3.50+ atoms to form distorted OMg2Ni3 trigonal bipyramids that share corners with two equivalent OMg2Ni3 square pyramids, an edgeedge with one OMg2Ni3 square pyramid, edges with two equivalent OMg2Ni3 trigonal bipyramids, and edges with two equivalent OMgNi3 trigonal pyramids. In the seventh O2- site, O2- is bonded to two equivalent Mg2+ and three Ni+3.50+ atoms to form OMg2Ni3 square pyramids that share corners with two equivalent OMg2Ni3 trigonal bipyramids, edges with two equivalent OMg2Ni3 square pyramids, an edgeedge with one OMg2Ni3 trigonal bipyramid, and edges with two equivalent OMgNi3 trigonal pyramids. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to three Ni+3.50+ atoms.