DOE OSTI2020
Mg(NiO2)2 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to five O2- atoms to form MgO5 square pyramids that share corners with four NiO6 octahedra, corners with four NiO5 square pyramids, an edgeedge with one NiO5 square pyramid, edges with two equivalent MgO5 square pyramids, and a faceface with one NiO6 octahedra. The corner-sharing octahedra tilt angles range from 39–59°. There are a spread of Mg–O bond distances ranging from 1.99–2.11 Å. In the second Mg2+ site, Mg2+ is bonded to five O2- atoms to form MgO5 square pyramids that share corners with four NiO6 octahedra, corners with four NiO5 square pyramids, an edgeedge with one NiO5 square pyramid, edges with two equivalent MgO5 square pyramids, and a faceface with one NiO6 octahedra. The corner-sharing octahedra tilt angles range from 39–59°. There are a spread of Mg–O bond distances ranging from 1.99–2.11 Å. There are four inequivalent Ni3+ sites. In the first Ni3+ site, Ni3+ is bonded to five O2- atoms to form NiO5 square pyramids that share corners with four NiO6 octahedra, corners with four MgO5 square pyramids, an edgeedge with one MgO5 square pyramid, and edges with two equivalent NiO5 square pyramids. The corner-sharing octahedra tilt angles range from 49–54°. There are a spread of Ni–O bond distances ranging from 1.92–2.00 Å. In the second Ni3+ site, Ni3+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with four MgO5 square pyramids, corners with four NiO5 square pyramids, edges with four NiO6 octahedra, and a faceface with one MgO5 square pyramid. There are a spread of Ni–O bond distances ranging from 1.88–2.05 Å. In the third Ni3+ site, Ni3+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with four MgO5 square pyramids, corners with four NiO5 square pyramids, edges with four NiO6 octahedra, and a faceface with one MgO5 square pyramid. There are a spread of Ni–O bond distances ranging from 1.89–2.04 Å. In the fourth Ni3+ site, Ni3+ is bonded to five O2- atoms to form NiO5 square pyramids that share corners with four NiO6 octahedra, corners with four MgO5 square pyramids, an edgeedge with one MgO5 square pyramid, and edges with two equivalent NiO5 square pyramids. The corner-sharing octahedra tilt angles range from 49–54°. There are a spread of Ni–O bond distances ranging from 1.92–2.00 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to one Mg2+ and three Ni3+ atoms to form distorted OMgNi3 trigonal pyramids that share a cornercorner with one OMg2Ni3 trigonal bipyramid, corners with two equivalent OMgNi3 trigonal pyramids, and edges with two equivalent OMg2Ni3 trigonal bipyramids. In the second O2- site, O2- is bonded in a trigonal planar geometry to three Ni3+ atoms. In the third O2- site, O2- is bonded in a trigonal planar geometry to three Ni3+ atoms. In the fourth O2- site, O2- is bonded to one Mg2+ and three Ni3+ atoms to form distorted OMgNi3 trigonal pyramids that share a cornercorner with one OMg2Ni3 trigonal bipyramid, corners with two equivalent OMgNi3 trigonal pyramids, and edges with two equivalent OMg2Ni3 trigonal bipyramids. In the fifth O2- site, O2- is bonded in a square co-planar geometry to two equivalent Mg2+ and two equivalent Ni3+ atoms. In the sixth O2- site, O2- is bonded to two equivalent Mg2+ and three Ni3+ atoms to form distorted OMg2Ni3 trigonal bipyramids that share a cornercorner with one OMgNi3 trigonal pyramid, edges with four OMg2Ni3 trigonal bipyramids, and edges with two equivalent OMgNi3 trigonal pyramids. In the seventh O2- site, O2- is bonded in a square co-planar geometry to two equivalent Mg2+ and two equivalent Ni3+ atoms. In the eighth O2- site, O2- is bonded to two equivalent Mg2+ and three Ni3+ atoms to form distorted OMg2Ni3 trigonal bipyramids that share a cornercorner with one OMgNi3 trigonal pyramid, edges with four OMg2Ni3 trigonal bipyramids, and edges with two equivalent OMgNi3 trigonal pyramids.