Mg(NiO2)2 is Spinel structured and crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form MgO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra, corners with three equivalent Ni(3)O6 octahedra, and corners with six equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-67°. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form NiO6 octahedra that share corners with six equivalent Mg(1)O4 tetrahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with four equivalent Ni(2)O6 octahedra. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with six equivalent Mg(1)O4 tetrahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. In the third Ni site, Ni(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form NiO6 octahedra that share corners with six equivalent Mg(1)O4 tetrahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with four equivalent Ni(2)O6 octahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Ni(1), one Ni(2), and one Ni(3) atom to form a mixture of distorted corner and edge-sharing OMgNi3 trigonal pyramids. In the second O site, O(2) is bonded to one Mg(1), one Ni(1), and two equivalent Ni(2) atoms to form a mixture of distorted corner and edge-sharing OMgNi3 trigonal pyramids. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Ni(3), and two equivalent Ni(2) atoms.
Mg(NiO2)2 is Spinel structured and crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form MgO4 tetrahedra that share corners with three equivalent Ni(1)O6 octahedra, corners with three equivalent Ni(3)O6 octahedra, and corners with six equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-67°. The Mg(1)-O(2) bond length is 1.97 Å. The Mg(1)-O(3) bond length is 1.94 Å. Both Mg(1)-O(1) bond lengths are 1.98 Å. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form NiO6 octahedra that share corners with six equivalent Mg(1)O4 tetrahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with four equivalent Ni(2)O6 octahedra. Both Ni(1)-O(2) bond lengths are 2.12 Å. All Ni(1)-O(1) bond lengths are 1.89 Å. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share corners with six equivalent Mg(1)O4 tetrahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. Both Ni(2)-O(1) bond lengths are 1.91 Å. Both Ni(2)-O(2) bond lengths are 1.88 Å. Both Ni(2)-O(3) bond lengths are 2.06 Å. In the third Ni site, Ni(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form NiO6 octahedra that share corners with six equivalent Mg(1)O4 tetrahedra, edges with two equivalent Ni(1)O6 octahedra, and edges with four equivalent Ni(2)O6 octahedra. Both Ni(3)-O(3) bond lengths are 1.85 Å. All Ni(3)-O(1) bond lengths are 2.01 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Ni(1), one Ni(2), and one Ni(3) atom to form a mixture of distorted corner and edge-sharing OMgNi3 trigonal pyramids. In the second O site, O(2) is bonded to one Mg(1), one Ni(1), and two equivalent Ni(2) atoms to form a mixture of distorted corner and edge-sharing OMgNi3 trigonal pyramids. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Ni(3), and two equivalent Ni(2) atoms.