Mg(NiO2)2 is Spinel-like structured and crystallizes in the trigonal R3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(3) and three equivalent O(4) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra and corners with nine equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-60°. In the second Mg site, Mg(2) is bonded to three equivalent O(1) and three equivalent O(4) atoms to form MgO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Ni(1)O4 tetrahedra, and edges with six equivalent Ni(2)O6 octahedra. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2) and three equivalent O(1) atoms to form NiO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra and corners with nine equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-60°. In the second Ni site, Ni(2) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Ni(1)O4 tetrahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with four equivalent Ni(2)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Ni(1), and two equivalent Ni(2) atoms to form distorted OMgNi3 trigonal pyramids that share corners with two equivalent O(1)MgNi3 trigonal pyramids, corners with seven equivalent O(4)Mg2Ni2 trigonal pyramids, and edges with two equivalent O(1)MgNi3 trigonal pyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ni(1) and three equivalent Ni(2) atoms. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1) and three equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Mg(2), and two equivalent Ni(2) atoms to form distorted OMg2Ni2 trigonal pyramids that share corners with two equivalent O(4)Mg2Ni2 trigonal pyramids, corners with seven equivalent O(1)MgNi3 trigonal pyramids, and edges with two equivalent O(4)Mg2Ni2 trigonal pyramids.
Mg(NiO2)2 is Spinel-like structured and crystallizes in the trigonal R3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(3) and three equivalent O(4) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra and corners with nine equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-60°. The Mg(1)-O(3) bond length is 1.94 Å. All Mg(1)-O(4) bond lengths are 1.97 Å. In the second Mg site, Mg(2) is bonded to three equivalent O(1) and three equivalent O(4) atoms to form MgO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Ni(1)O4 tetrahedra, and edges with six equivalent Ni(2)O6 octahedra. All Mg(2)-O(1) bond lengths are 2.08 Å. All Mg(2)-O(4) bond lengths are 2.04 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2) and three equivalent O(1) atoms to form NiO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra and corners with nine equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-60°. The Ni(1)-O(2) bond length is 1.82 Å. All Ni(1)-O(1) bond lengths are 1.92 Å. In the second Ni site, Ni(2) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Ni(1)O4 tetrahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with four equivalent Ni(2)O6 octahedra. The Ni(2)-O(2) bond length is 2.15 Å. The Ni(2)-O(3) bond length is 2.03 Å. Both Ni(2)-O(1) bond lengths are 1.97 Å. Both Ni(2)-O(4) bond lengths are 1.91 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Ni(1), and two equivalent Ni(2) atoms to form distorted OMgNi3 trigonal pyramids that share corners with two equivalent O(1)MgNi3 trigonal pyramids, corners with seven equivalent O(4)Mg2Ni2 trigonal pyramids, and edges with two equivalent O(1)MgNi3 trigonal pyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ni(1) and three equivalent Ni(2) atoms. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mg(1) and three equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Mg(2), and two equivalent Ni(2) atoms to form distorted OMg2Ni2 trigonal pyramids that share corners with two equivalent O(4)Mg2Ni2 trigonal pyramids, corners with seven equivalent O(1)MgNi3 trigonal pyramids, and edges with two equivalent O(4)Mg2Ni2 trigonal pyramids.