Mg(CoO2)4 crystallizes in the trigonal R3m space group. Mg(1) is bonded in a 6-coordinate geometry to three equivalent O(2) and three equivalent O(3) atoms. 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 edge-sharing CoO6 octahedra. In the second Co site, Co(2) is bonded in a distorted rectangular see-saw-like geometry to one O(4) and three equivalent O(3) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to three equivalent Co(1) atoms. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Mg(1) and two equivalent Co(1) atoms. In the third O site, O(3) is bonded to one Mg(1), one Co(2), and two equivalent Co(1) atoms to form OMgCo3 trigonal pyramids that share  a cornercorner with one O(4)Co4 trigonal pyramid, corners with two equivalent O(3)MgCo3 trigonal pyramids,  an edgeedge with one O(4)Co4 trigonal pyramid, and edges with two equivalent O(3)MgCo3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Co(2) and three equivalent Co(1) atoms to form a mixture of distorted edge and corner-sharing OCo4 trigonal pyramids.
Mg(CoO2)4 crystallizes in the trigonal R3m space group. Mg(1) is bonded in a 6-coordinate geometry to three equivalent O(2) and three equivalent O(3) atoms. All Mg(1)-O(2) bond lengths are 1.92 Å. All Mg(1)-O(3) bond lengths are 2.27 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 edge-sharing CoO6 octahedra. The Co(1)-O(1) bond length is 1.90 Å. The Co(1)-O(4) bond length is 1.98 Å. Both Co(1)-O(2) bond lengths are 1.85 Å. Both Co(1)-O(3) bond lengths are 1.91 Å. In the second Co site, Co(2) is bonded in a distorted rectangular see-saw-like geometry to one O(4) and three equivalent O(3) atoms. The Co(2)-O(4) bond length is 1.93 Å. All Co(2)-O(3) bond lengths are 2.00 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to three equivalent Co(1) atoms. In the second O site, O(2) is bonded in a trigonal non-coplanar geometry to one Mg(1) and two equivalent Co(1) atoms. In the third O site, O(3) is bonded to one Mg(1), one Co(2), and two equivalent Co(1) atoms to form OMgCo3 trigonal pyramids that share  a cornercorner with one O(4)Co4 trigonal pyramid, corners with two equivalent O(3)MgCo3 trigonal pyramids,  an edgeedge with one O(4)Co4 trigonal pyramid, and edges with two equivalent O(3)MgCo3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Co(2) and three equivalent Co(1) atoms to form a mixture of distorted edge and corner-sharing OCo4 trigonal pyramids.