MgFe2(CoO2)4 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Co(3)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-6°. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and edges with two equivalent Co(3)O6 octahedra. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form CoO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. In the second Co site, Co(2) is bonded in a distorted rectangular see-saw-like geometry to one O(2), one O(3), and two equivalent O(1) atoms. In the third Co site, Co(3) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CoO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-6°. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(1), one Co(1), one Co(2), and one Co(3) atom to form OMgFeCo3 square pyramids that share  a cornercorner with one O(2)MgFe2Co2 square pyramid, corners with five equivalent O(1)MgFeCo3 square pyramids, corners with three equivalent O(3)Fe2Co2 tetrahedra, edges with three equivalent O(2)MgFe2Co2 square pyramids, edges with three equivalent O(1)MgFeCo3 square pyramids, and  an edgeedge with one O(3)Fe2Co2 tetrahedra. In the second O site, O(2) is bonded to one Mg(1), two equivalent Fe(1), one Co(2), and one Co(3) atom to form OMgFe2Co2 square pyramids that share corners with two equivalent O(1)MgFeCo3 square pyramids, corners with four equivalent O(2)MgFe2Co2 square pyramids, corners with three equivalent O(3)Fe2Co2 tetrahedra, edges with six equivalent O(1)MgFeCo3 square pyramids, and  an edgeedge with one O(3)Fe2Co2 tetrahedra. In the third O site, O(3) is bonded to two equivalent Fe(1), one Co(1), and one Co(2) atom to form distorted OFe2Co2 tetrahedra that share corners with three equivalent O(2)MgFe2Co2 square pyramids, corners with six equivalent O(1)MgFeCo3 square pyramids, corners with three equivalent O(3)Fe2Co2 tetrahedra,  an edgeedge with one O(2)MgFe2Co2 square pyramid, and edges with two equivalent O(1)MgFeCo3 square pyramids.
MgFe2(CoO2)4 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Co(3)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-6°. Both Mg(1)-O(2) bond lengths are 2.09 Å. All Mg(1)-O(1) bond lengths are 2.13 Å. Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and edges with two equivalent Co(3)O6 octahedra. Both Fe(1)-O(1) bond lengths are 2.09 Å. Both Fe(1)-O(2) bond lengths are 2.10 Å. Both Fe(1)-O(3) bond lengths are 1.98 Å. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form CoO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. Both Co(1)-O(3) bond lengths are 2.00 Å. All Co(1)-O(1) bond lengths are 2.18 Å. In the second Co site, Co(2) is bonded in a distorted rectangular see-saw-like geometry to one O(2), one O(3), and two equivalent O(1) atoms. The Co(2)-O(2) bond length is 2.16 Å. The Co(2)-O(3) bond length is 1.88 Å. Both Co(2)-O(1) bond lengths are 2.05 Å. In the third Co site, Co(3) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CoO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-6°. Both Co(3)-O(2) bond lengths are 2.31 Å. All Co(3)-O(1) bond lengths are 2.18 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(1), one Co(1), one Co(2), and one Co(3) atom to form OMgFeCo3 square pyramids that share  a cornercorner with one O(2)MgFe2Co2 square pyramid, corners with five equivalent O(1)MgFeCo3 square pyramids, corners with three equivalent O(3)Fe2Co2 tetrahedra, edges with three equivalent O(2)MgFe2Co2 square pyramids, edges with three equivalent O(1)MgFeCo3 square pyramids, and  an edgeedge with one O(3)Fe2Co2 tetrahedra. In the second O site, O(2) is bonded to one Mg(1), two equivalent Fe(1), one Co(2), and one Co(3) atom to form OMgFe2Co2 square pyramids that share corners with two equivalent O(1)MgFeCo3 square pyramids, corners with four equivalent O(2)MgFe2Co2 square pyramids, corners with three equivalent O(3)Fe2Co2 tetrahedra, edges with six equivalent O(1)MgFeCo3 square pyramids, and  an edgeedge with one O(3)Fe2Co2 tetrahedra. In the third O site, O(3) is bonded to two equivalent Fe(1), one Co(1), and one Co(2) atom to form distorted OFe2Co2 tetrahedra that share corners with three equivalent O(2)MgFe2Co2 square pyramids, corners with six equivalent O(1)MgFeCo3 square pyramids, corners with three equivalent O(3)Fe2Co2 tetrahedra,  an edgeedge with one O(2)MgFe2Co2 square pyramid, and edges with two equivalent O(1)MgFeCo3 square pyramids.