MgCoO2 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form MgO5 trigonal bipyramids that share corners with four equivalent Mg(2)O4 tetrahedra, corners with two equivalent Co(2)O5 trigonal bipyramids, edges with two equivalent Mg(1)O5 trigonal bipyramids, and  a faceface with one Co(2)O5 trigonal bipyramid. In the second Mg site, Mg(2) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form MgO4 tetrahedra that share corners with two equivalent Mg(2)O4 tetrahedra, corners with four equivalent Mg(1)O5 trigonal bipyramids, corners with four equivalent Co(2)O5 trigonal bipyramids, and  an edgeedge with one Co(2)O5 trigonal bipyramid. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(3) atoms. In the second Co site, Co(2) is bonded to one O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted CoO5 trigonal bipyramids that share corners with four equivalent Mg(2)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids,  an edgeedge with one Mg(2)O4 tetrahedra, edges with two equivalent Co(2)O5 trigonal bipyramids, and  a faceface with one Mg(1)O5 trigonal bipyramid. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Co(2), and two equivalent Co(1) atoms to form distorted OMgCo3 tetrahedra that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with four equivalent O(3)Mg3Co2 trigonal bipyramids, and  an edgeedge with one O(3)Mg3Co2 trigonal bipyramid. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(2) and two equivalent Co(2) atoms. In the third O site, O(3) is bonded to one Mg(2), two equivalent Mg(1), and two equivalent Co(1) atoms to form distorted OMg3Co2 trigonal bipyramids that share corners with four equivalent O(1)MgCo3 tetrahedra,  an edgeedge with one O(1)MgCo3 tetrahedra, and edges with two equivalent O(3)Mg3Co2 trigonal bipyramids. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Mg(2), two equivalent Mg(1), and two equivalent Co(2) atoms.
MgCoO2 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form MgO5 trigonal bipyramids that share corners with four equivalent Mg(2)O4 tetrahedra, corners with two equivalent Co(2)O5 trigonal bipyramids, edges with two equivalent Mg(1)O5 trigonal bipyramids, and  a faceface with one Co(2)O5 trigonal bipyramid. The Mg(1)-O(1) bond length is 2.05 Å. There is one shorter (2.11 Å) and one longer (2.13 Å) Mg(1)-O(3) bond length. There is one shorter (2.05 Å) and one longer (2.07 Å) Mg(1)-O(4) bond length. In the second Mg site, Mg(2) is bonded to one O(3), one O(4), and two equivalent O(2) atoms to form MgO4 tetrahedra that share corners with two equivalent Mg(2)O4 tetrahedra, corners with four equivalent Mg(1)O5 trigonal bipyramids, corners with four equivalent Co(2)O5 trigonal bipyramids, and  an edgeedge with one Co(2)O5 trigonal bipyramid. The Mg(2)-O(3) bond length is 2.00 Å. The Mg(2)-O(4) bond length is 1.96 Å. There is one shorter (1.96 Å) and one longer (1.98 Å) Mg(2)-O(2) bond length. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded in a square co-planar geometry to two equivalent O(1) and two equivalent O(3) atoms. There is one shorter (1.92 Å) and one longer (1.96 Å) Co(1)-O(1) bond length. There is one shorter (2.11 Å) and one longer (2.14 Å) Co(1)-O(3) bond length. In the second Co site, Co(2) is bonded to one O(1), two equivalent O(2), and two equivalent O(4) atoms to form distorted CoO5 trigonal bipyramids that share corners with four equivalent Mg(2)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids,  an edgeedge with one Mg(2)O4 tetrahedra, edges with two equivalent Co(2)O5 trigonal bipyramids, and  a faceface with one Mg(1)O5 trigonal bipyramid. The Co(2)-O(1) bond length is 2.06 Å. There is one shorter (2.03 Å) and one longer (2.04 Å) Co(2)-O(2) bond length. There is one shorter (2.17 Å) and one longer (2.32 Å) Co(2)-O(4) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Co(2), and two equivalent Co(1) atoms to form distorted OMgCo3 tetrahedra that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with four equivalent O(3)Mg3Co2 trigonal bipyramids, and  an edgeedge with one O(3)Mg3Co2 trigonal bipyramid. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(2) and two equivalent Co(2) atoms. In the third O site, O(3) is bonded to one Mg(2), two equivalent Mg(1), and two equivalent Co(1) atoms to form distorted OMg3Co2 trigonal bipyramids that share corners with four equivalent O(1)MgCo3 tetrahedra,  an edgeedge with one O(1)MgCo3 tetrahedra, and edges with two equivalent O(3)Mg3Co2 trigonal bipyramids. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Mg(2), two equivalent Mg(1), and two equivalent Co(2) atoms.