MgCo2O4 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form MgO5 square pyramids that share corners with two equivalent Co(1)O6 octahedra, corners with four equivalent Co(2)O6 octahedra, edges with three equivalent Co(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-60°. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form CoO6 octahedra that share corners with four equivalent Co(2)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with four equivalent Co(1)O6 octahedra, and edges with three equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 50-58°. In the second Co site, Co(2) is bonded to one O(1), two equivalent O(2), and three equivalent O(4) atoms to form CoO6 octahedra that share corners with four equivalent Co(1)O6 octahedra, corners with four equivalent Mg(1)O5 square pyramids, edges with four equivalent Co(2)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 50-58°. 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 OMgCo3 trigonal pyramids that share corners with two equivalent O(3)Mg2Co3 square pyramids,  a cornercorner with one O(4)Mg2Co3 trigonal bipyramid, corners with two equivalent O(1)MgCo3 trigonal pyramids, edges with three equivalent O(3)Mg2Co3 square pyramids, and edges with two equivalent O(4)Mg2Co3 trigonal bipyramids. In the second O site, O(2) is bonded in a trigonal planar geometry to one Co(1) and two equivalent Co(2) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1) and three equivalent Co(1) atoms to form OMg2Co3 square pyramids that share corners with two equivalent O(4)Mg2Co3 trigonal bipyramids, corners with two equivalent O(1)MgCo3 trigonal pyramids, edges with four equivalent O(3)Mg2Co3 square pyramids,  an edgeedge with one O(4)Mg2Co3 trigonal bipyramid, and edges with three equivalent O(1)MgCo3 trigonal pyramids. In the fourth O site, O(4) is bonded to two equivalent Mg(1) and three equivalent Co(2) atoms to form distorted OMg2Co3 trigonal bipyramids that share corners with two equivalent O(3)Mg2Co3 square pyramids,  a cornercorner with one O(1)MgCo3 trigonal pyramid,  an edgeedge with one O(3)Mg2Co3 square pyramid, edges with four equivalent O(4)Mg2Co3 trigonal bipyramids, and edges with two equivalent O(1)MgCo3 trigonal pyramids.
MgCo2O4 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form MgO5 square pyramids that share corners with two equivalent Co(1)O6 octahedra, corners with four equivalent Co(2)O6 octahedra, edges with three equivalent Co(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-60°. The Mg(1)-O(1) bond length is 2.06 Å. Both Mg(1)-O(3) bond lengths are 2.02 Å. Both Mg(1)-O(4) bond lengths are 2.04 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form CoO6 octahedra that share corners with four equivalent Co(2)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with four equivalent Co(1)O6 octahedra, and edges with three equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 50-58°. The Co(1)-O(2) bond length is 1.85 Å. Both Co(1)-O(1) bond lengths are 1.87 Å. There are two shorter (2.00 Å) and one longer (2.11 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 three equivalent O(4) atoms to form CoO6 octahedra that share corners with four equivalent Co(1)O6 octahedra, corners with four equivalent Mg(1)O5 square pyramids, edges with four equivalent Co(2)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 50-58°. The Co(2)-O(1) bond length is 1.96 Å. Both Co(2)-O(2) bond lengths are 1.89 Å. There is one shorter (1.89 Å) and two longer (2.01 Å) Co(2)-O(4) bond lengths. 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 OMgCo3 trigonal pyramids that share corners with two equivalent O(3)Mg2Co3 square pyramids,  a cornercorner with one O(4)Mg2Co3 trigonal bipyramid, corners with two equivalent O(1)MgCo3 trigonal pyramids, edges with three equivalent O(3)Mg2Co3 square pyramids, and edges with two equivalent O(4)Mg2Co3 trigonal bipyramids. In the second O site, O(2) is bonded in a trigonal planar geometry to one Co(1) and two equivalent Co(2) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1) and three equivalent Co(1) atoms to form OMg2Co3 square pyramids that share corners with two equivalent O(4)Mg2Co3 trigonal bipyramids, corners with two equivalent O(1)MgCo3 trigonal pyramids, edges with four equivalent O(3)Mg2Co3 square pyramids,  an edgeedge with one O(4)Mg2Co3 trigonal bipyramid, and edges with three equivalent O(1)MgCo3 trigonal pyramids. In the fourth O site, O(4) is bonded to two equivalent Mg(1) and three equivalent Co(2) atoms to form distorted OMg2Co3 trigonal bipyramids that share corners with two equivalent O(3)Mg2Co3 square pyramids,  a cornercorner with one O(1)MgCo3 trigonal pyramid,  an edgeedge with one O(3)Mg2Co3 square pyramid, edges with four equivalent O(4)Mg2Co3 trigonal bipyramids, and edges with two equivalent O(1)MgCo3 trigonal pyramids.