MgCoO2 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Co(1)O5 trigonal bipyramids, and edges with two equivalent Mg(1)O5 trigonal bipyramids. In the second Mg site, Mg(2) is bonded to one O(1), two equivalent O(5), and two equivalent O(8) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Co(1)O5 trigonal bipyramids, corners with two equivalent Co(3)O5 trigonal bipyramids,  an edgeedge with one Co(1)O5 trigonal bipyramid, edges with two equivalent Mg(2)O5 trigonal bipyramids, and  a faceface with one Co(3)O5 trigonal bipyramid. In the third Mg site, Mg(3) is bonded to one O(7), one O(8), and two equivalent O(3) atoms to form MgO4 tetrahedra that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, and corners with two equivalent Co(3)O5 trigonal bipyramids. In the fourth Mg site, Mg(4) is bonded in a rectangular see-saw-like geometry to one O(5), one O(6), and two equivalent O(2) atoms. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form distorted CoO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Co(3)O5 trigonal bipyramids,  an edgeedge with one Mg(2)O5 trigonal bipyramid, and edges with two equivalent Co(1)O5 trigonal bipyramids. In the second Co site, Co(2) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(3), and two equivalent O(6) atoms. In the third Co site, Co(3) is bonded to one O(1), two equivalent O(2), and two equivalent O(8) atoms to form distorted CoO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Co(1)O5 trigonal bipyramids, edges with two equivalent Co(3)O5 trigonal bipyramids, and  a faceface with one Mg(2)O5 trigonal bipyramid. In the fourth Co site, Co(4) is bonded in a distorted square co-planar geometry to two equivalent O(1) and two equivalent O(7) atoms. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Co(3), and two equivalent Co(4) atoms to form OMgCo3 tetrahedra that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with two equivalent O(2)Mg2Co3 trigonal bipyramids, corners with two equivalent O(5)Mg3Co2 trigonal bipyramids, corners with two equivalent O(7)Mg3Co2 trigonal bipyramids, and  an edgeedge with one O(7)Mg3Co2 trigonal bipyramid. In the second O site, O(2) is bonded to two equivalent Mg(4), one Co(1), and two equivalent Co(3) atoms to form distorted OMg2Co3 trigonal bipyramids that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with two equivalent O(4)MgCo3 tetrahedra, edges with two equivalent O(2)Mg2Co3 trigonal bipyramids, and edges with two equivalent O(5)Mg3Co2 trigonal bipyramids. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Mg(3) and two equivalent Co(2) atoms. In the fourth O site, O(4) 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(4)MgCo3 tetrahedra, corners with two equivalent O(2)Mg2Co3 trigonal bipyramids, corners with two equivalent O(5)Mg3Co2 trigonal bipyramids, corners with two equivalent O(7)Mg3Co2 trigonal bipyramids, and  an edgeedge with one O(5)Mg3Co2 trigonal bipyramid. In the fifth O site, O(5) is bonded to one Mg(4), two equivalent Mg(2), and two equivalent Co(1) atoms to form distorted OMg3Co2 trigonal bipyramids that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with two equivalent O(4)MgCo3 tetrahedra,  an edgeedge with one O(4)MgCo3 tetrahedra, edges with two equivalent O(2)Mg2Co3 trigonal bipyramids, and edges with two equivalent O(5)Mg3Co2 trigonal bipyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Mg(4), two equivalent Mg(1), and two equivalent Co(2) atoms. In the seventh O site, O(7) is bonded to one Mg(3), two equivalent Mg(1), and two equivalent Co(4) atoms to form distorted OMg3Co2 trigonal bipyramids that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with two equivalent O(4)MgCo3 tetrahedra,  an edgeedge with one O(1)MgCo3 tetrahedra, and edges with two equivalent O(7)Mg3Co2 trigonal bipyramids. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Mg(3), two equivalent Mg(2), and two equivalent Co(3) atoms.
MgCoO2 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Co(1)O5 trigonal bipyramids, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The Mg(1)-O(4) bond length is 2.06 Å. There is one shorter (2.06 Å) and one longer (2.07 Å) Mg(1)-O(6) bond length. Both Mg(1)-O(7) bond lengths are 2.10 Å. In the second Mg site, Mg(2) is bonded to one O(1), two equivalent O(5), and two equivalent O(8) atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Co(1)O5 trigonal bipyramids, corners with two equivalent Co(3)O5 trigonal bipyramids,  an edgeedge with one Co(1)O5 trigonal bipyramid, edges with two equivalent Mg(2)O5 trigonal bipyramids, and  a faceface with one Co(3)O5 trigonal bipyramid. The Mg(2)-O(1) bond length is 2.06 Å. There is one shorter (2.05 Å) and one longer (2.06 Å) Mg(2)-O(5) bond length. There is one shorter (2.10 Å) and one longer (2.12 Å) Mg(2)-O(8) bond length. In the third Mg site, Mg(3) is bonded to one O(7), one O(8), and two equivalent O(3) atoms to form MgO4 tetrahedra that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, and corners with two equivalent Co(3)O5 trigonal bipyramids. The Mg(3)-O(7) bond length is 2.01 Å. The Mg(3)-O(8) bond length is 1.94 Å. Both Mg(3)-O(3) bond lengths are 1.98 Å. In the fourth Mg site, Mg(4) is bonded in a rectangular see-saw-like geometry to one O(5), one O(6), and two equivalent O(2) atoms. The Mg(4)-O(5) bond length is 1.99 Å. The Mg(4)-O(6) bond length is 1.93 Å. Both Mg(4)-O(2) bond lengths are 2.01 Å. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form distorted CoO5 trigonal bipyramids that share corners with two equivalent Mg(1)O5 trigonal bipyramids, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Co(3)O5 trigonal bipyramids,  an edgeedge with one Mg(2)O5 trigonal bipyramid, and edges with two equivalent Co(1)O5 trigonal bipyramids. The Co(1)-O(2) bond length is 2.20 Å. There is one shorter (1.96 Å) and one longer (1.99 Å) Co(1)-O(4) bond length. There is one shorter (2.18 Å) and one longer (2.24 Å) Co(1)-O(5) bond length. In the second Co site, Co(2) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(3), and two equivalent O(6) atoms. The Co(2)-O(4) bond length is 2.00 Å. There is one shorter (2.05 Å) and one longer (2.07 Å) Co(2)-O(3) bond length. There is one shorter (2.16 Å) and one longer (2.29 Å) Co(2)-O(6) bond length. In the third Co site, Co(3) is bonded to one O(1), two equivalent O(2), and two equivalent O(8) atoms to form distorted CoO5 trigonal bipyramids that share corners with two equivalent Mg(3)O4 tetrahedra, corners with two equivalent Mg(2)O5 trigonal bipyramids, corners with two equivalent Co(1)O5 trigonal bipyramids, edges with two equivalent Co(3)O5 trigonal bipyramids, and  a faceface with one Mg(2)O5 trigonal bipyramid. The Co(3)-O(1) bond length is 2.00 Å. There is one shorter (2.10 Å) and one longer (2.11 Å) Co(3)-O(2) bond length. There is one shorter (2.12 Å) and one longer (2.26 Å) Co(3)-O(8) bond length. In the fourth Co site, Co(4) is bonded in a distorted square co-planar geometry to two equivalent O(1) and two equivalent O(7) atoms. There is one shorter (1.93 Å) and one longer (1.95 Å) Co(4)-O(1) bond length. There is one shorter (2.12 Å) and one longer (2.13 Å) Co(4)-O(7) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Co(3), and two equivalent Co(4) atoms to form OMgCo3 tetrahedra that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with two equivalent O(2)Mg2Co3 trigonal bipyramids, corners with two equivalent O(5)Mg3Co2 trigonal bipyramids, corners with two equivalent O(7)Mg3Co2 trigonal bipyramids, and  an edgeedge with one O(7)Mg3Co2 trigonal bipyramid. In the second O site, O(2) is bonded to two equivalent Mg(4), one Co(1), and two equivalent Co(3) atoms to form distorted OMg2Co3 trigonal bipyramids that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with two equivalent O(4)MgCo3 tetrahedra, edges with two equivalent O(2)Mg2Co3 trigonal bipyramids, and edges with two equivalent O(5)Mg3Co2 trigonal bipyramids. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Mg(3) and two equivalent Co(2) atoms. In the fourth O site, O(4) 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(4)MgCo3 tetrahedra, corners with two equivalent O(2)Mg2Co3 trigonal bipyramids, corners with two equivalent O(5)Mg3Co2 trigonal bipyramids, corners with two equivalent O(7)Mg3Co2 trigonal bipyramids, and  an edgeedge with one O(5)Mg3Co2 trigonal bipyramid. In the fifth O site, O(5) is bonded to one Mg(4), two equivalent Mg(2), and two equivalent Co(1) atoms to form distorted OMg3Co2 trigonal bipyramids that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with two equivalent O(4)MgCo3 tetrahedra,  an edgeedge with one O(4)MgCo3 tetrahedra, edges with two equivalent O(2)Mg2Co3 trigonal bipyramids, and edges with two equivalent O(5)Mg3Co2 trigonal bipyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Mg(4), two equivalent Mg(1), and two equivalent Co(2) atoms. In the seventh O site, O(7) is bonded to one Mg(3), two equivalent Mg(1), and two equivalent Co(4) atoms to form distorted OMg3Co2 trigonal bipyramids that share corners with two equivalent O(1)MgCo3 tetrahedra, corners with two equivalent O(4)MgCo3 tetrahedra,  an edgeedge with one O(1)MgCo3 tetrahedra, and edges with two equivalent O(7)Mg3Co2 trigonal bipyramids. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Mg(3), two equivalent Mg(2), and two equivalent Co(3) atoms.