MgCo2O4 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form distorted MgO6 pentagonal pyramids that share corners with six equivalent Co(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 5-15°. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four 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(2), and four equivalent O(3) atoms to form CoO6 octahedra that share corners with three equivalent Mg(1)O6 pentagonal pyramids, edges with two equivalent Co(1)O6 octahedra, edges with four equivalent Co(2)O6 octahedra, and  an edgeedge with one Mg(1)O6 pentagonal pyramid. In the second Co site, Co(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CoO6 octahedra that share edges with two equivalent Co(2)O6 octahedra, edges with four equivalent Co(1)O6 octahedra, and edges with two equivalent Mg(1)O6 pentagonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(1), and two equivalent Co(2) atoms. In the second O site, O(2) is bonded to one Mg(2), one Co(1), and two equivalent Co(2) atoms to form OMgCo3 trigonal pyramids that share corners with four equivalent O(3)Mg2Co3 trigonal bipyramids, corners with three equivalent O(2)MgCo3 trigonal pyramids, and edges with four equivalent O(3)Mg2Co3 trigonal bipyramids. In the third O site, O(3) is bonded to one Mg(1), one Mg(2), one Co(2), and two equivalent Co(1) atoms to form OMg2Co3 trigonal bipyramids that share corners with five equivalent O(3)Mg2Co3 trigonal bipyramids, corners with two equivalent O(2)MgCo3 trigonal pyramids, edges with four equivalent O(3)Mg2Co3 trigonal bipyramids, and edges with two equivalent O(2)MgCo3 trigonal pyramids.
MgCo2O4 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form distorted MgO6 pentagonal pyramids that share corners with six equivalent Co(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 5-15°. Both Mg(1)-O(1) bond lengths are 2.05 Å. All Mg(1)-O(3) bond lengths are 2.21 Å. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(3) atoms. Both Mg(2)-O(2) bond lengths are 2.07 Å. All Mg(2)-O(3) bond lengths are 2.21 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form CoO6 octahedra that share corners with three equivalent Mg(1)O6 pentagonal pyramids, edges with two equivalent Co(1)O6 octahedra, edges with four equivalent Co(2)O6 octahedra, and  an edgeedge with one Mg(1)O6 pentagonal pyramid. The Co(1)-O(1) bond length is 1.92 Å. The Co(1)-O(2) bond length is 1.90 Å. There are two shorter (1.92 Å) and two longer (1.98 Å) Co(1)-O(3) bond lengths. In the second Co site, Co(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CoO6 octahedra that share edges with two equivalent Co(2)O6 octahedra, edges with four equivalent Co(1)O6 octahedra, and edges with two equivalent Mg(1)O6 pentagonal pyramids. Both Co(2)-O(1) bond lengths are 1.90 Å. Both Co(2)-O(2) bond lengths are 1.93 Å. Both Co(2)-O(3) bond lengths are 1.95 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(1), and two equivalent Co(2) atoms. In the second O site, O(2) is bonded to one Mg(2), one Co(1), and two equivalent Co(2) atoms to form OMgCo3 trigonal pyramids that share corners with four equivalent O(3)Mg2Co3 trigonal bipyramids, corners with three equivalent O(2)MgCo3 trigonal pyramids, and edges with four equivalent O(3)Mg2Co3 trigonal bipyramids. In the third O site, O(3) is bonded to one Mg(1), one Mg(2), one Co(2), and two equivalent Co(1) atoms to form OMg2Co3 trigonal bipyramids that share corners with five equivalent O(3)Mg2Co3 trigonal bipyramids, corners with two equivalent O(2)MgCo3 trigonal pyramids, edges with four equivalent O(3)Mg2Co3 trigonal bipyramids, and edges with two equivalent O(2)MgCo3 trigonal pyramids.