Mg(CoO2)4 crystallizes in the trigonal R3m space group. Mg(1) is bonded to one O(1) and three equivalent O(2) atoms to form MgO4 tetrahedra that share corners with nine equivalent Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 57-58°. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form CoO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Co(2)O4 tetrahedra, and edges with four equivalent Co(1)O6 octahedra. In the second Co site, Co(2) is bonded to one O(4) and three equivalent O(3) atoms to form corner-sharing CoO4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-58°. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1) and three equivalent Co(1) atoms to form distorted corner-sharing OMgCo3 trigonal pyramids. In the second O site, O(2) is bonded in a trigonal planar geometry to one Mg(1) and two equivalent Co(1) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Co(2) and two equivalent Co(1) atoms. In the fourth O site, O(4) is bonded to one Co(2) and three equivalent Co(1) atoms to form distorted corner-sharing OCo4 trigonal pyramids.
Mg(CoO2)4 crystallizes in the trigonal R3m space group. Mg(1) is bonded to one O(1) and three equivalent O(2) atoms to form MgO4 tetrahedra that share corners with nine equivalent Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 57-58°. The Mg(1)-O(1) bond length is 2.01 Å. All Mg(1)-O(2) bond lengths are 1.96 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form CoO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Co(2)O4 tetrahedra, and edges with four equivalent Co(1)O6 octahedra. The Co(1)-O(1) bond length is 1.93 Å. The Co(1)-O(4) bond length is 1.96 Å. Both Co(1)-O(2) bond lengths are 1.84 Å. Both Co(1)-O(3) bond lengths are 1.87 Å. In the second Co site, Co(2) is bonded to one O(4) and three equivalent O(3) atoms to form corner-sharing CoO4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-58°. The Co(2)-O(4) bond length is 2.00 Å. All Co(2)-O(3) bond lengths are 1.92 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1) and three equivalent Co(1) atoms to form distorted corner-sharing OMgCo3 trigonal pyramids. In the second O site, O(2) is bonded in a trigonal planar geometry to one Mg(1) and two equivalent Co(1) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Co(2) and two equivalent Co(1) atoms. In the fourth O site, O(4) is bonded to one Co(2) and three equivalent Co(1) atoms to form distorted corner-sharing OCo4 trigonal pyramids.