MgFe(CoO3)2 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(3), one O(6), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra, corners with four equivalent Fe(1)O6 octahedra, 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(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-24°. Fe(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, 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(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-5°. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(6) atoms to form distorted CoO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, 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(2)O6 octahedra. The corner-sharing octahedral tilt angles are 22°. In the second Co site, Co(2) is bonded to one O(2), one O(6), two equivalent O(3), and two equivalent O(5) atoms to form distorted CoO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, 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(2)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a trigonal non-coplanar geometry to one Fe(1) and two equivalent Co(1) atoms. In the second O site, O(2) is bonded to two equivalent Mg(1), two equivalent Fe(1), and one Co(2) atom to form OMg2Fe2Co square pyramids that share corners with four equivalent O(4)Mg2Fe2Co square pyramids, edges with two equivalent O(2)Mg2Fe2Co square pyramids, edges with two equivalent O(4)Mg2Fe2Co square pyramids, and edges with two equivalent O(3)MgCo3 trigonal pyramids. In the third O site, O(3) is bonded to one Mg(1), one Co(1), and two equivalent Co(2) atoms to form OMgCo3 trigonal pyramids that share corners with three equivalent O(4)Mg2Fe2Co square pyramids, corners with two equivalent O(3)MgCo3 trigonal pyramids, and edges with two equivalent O(2)Mg2Fe2Co square pyramids. In the fourth O site, O(4) is bonded to two equivalent Mg(1), two equivalent Fe(1), and one Co(1) atom to form OMg2Fe2Co square pyramids that share corners with four equivalent O(2)Mg2Fe2Co square pyramids, corners with three equivalent O(3)MgCo3 trigonal pyramids, edges with two equivalent O(2)Mg2Fe2Co square pyramids, and edges with two equivalent O(4)Mg2Fe2Co square pyramids. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1) and two equivalent Co(2) atoms. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(2), and two equivalent Co(1) atoms.
MgFe(CoO3)2 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(3), one O(6), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share  a cornercorner with one Co(1)O6 octahedra,  a cornercorner with one Co(2)O6 octahedra, corners with four equivalent Fe(1)O6 octahedra, 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(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-24°. The Mg(1)-O(3) bond length is 2.16 Å. The Mg(1)-O(6) bond length is 2.13 Å. Both Mg(1)-O(2) bond lengths are 2.09 Å. Both Mg(1)-O(4) bond lengths are 2.09 Å. Fe(1) is bonded to one O(1), one O(5), two equivalent O(2), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, 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(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-5°. The Fe(1)-O(1) bond length is 2.10 Å. The Fe(1)-O(5) bond length is 2.01 Å. Both Fe(1)-O(2) bond lengths are 2.04 Å. Both Fe(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(3), one O(4), two equivalent O(1), and two equivalent O(6) atoms to form distorted CoO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, 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(2)O6 octahedra. The corner-sharing octahedral tilt angles are 22°. The Co(1)-O(3) bond length is 1.94 Å. The Co(1)-O(4) bond length is 2.27 Å. Both Co(1)-O(1) bond lengths are 1.88 Å. Both Co(1)-O(6) bond lengths are 1.93 Å. In the second Co site, Co(2) is bonded to one O(2), one O(6), two equivalent O(3), and two equivalent O(5) atoms to form distorted CoO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, 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(2)O6 octahedra. The corner-sharing octahedral tilt angles are 24°. The Co(2)-O(2) bond length is 2.24 Å. The Co(2)-O(6) bond length is 2.10 Å. Both Co(2)-O(3) bond lengths are 1.97 Å. Both Co(2)-O(5) bond lengths are 1.88 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a trigonal non-coplanar geometry to one Fe(1) and two equivalent Co(1) atoms. In the second O site, O(2) is bonded to two equivalent Mg(1), two equivalent Fe(1), and one Co(2) atom to form OMg2Fe2Co square pyramids that share corners with four equivalent O(4)Mg2Fe2Co square pyramids, edges with two equivalent O(2)Mg2Fe2Co square pyramids, edges with two equivalent O(4)Mg2Fe2Co square pyramids, and edges with two equivalent O(3)MgCo3 trigonal pyramids. In the third O site, O(3) is bonded to one Mg(1), one Co(1), and two equivalent Co(2) atoms to form OMgCo3 trigonal pyramids that share corners with three equivalent O(4)Mg2Fe2Co square pyramids, corners with two equivalent O(3)MgCo3 trigonal pyramids, and edges with two equivalent O(2)Mg2Fe2Co square pyramids. In the fourth O site, O(4) is bonded to two equivalent Mg(1), two equivalent Fe(1), and one Co(1) atom to form OMg2Fe2Co square pyramids that share corners with four equivalent O(2)Mg2Fe2Co square pyramids, corners with three equivalent O(3)MgCo3 trigonal pyramids, edges with two equivalent O(2)Mg2Fe2Co square pyramids, and edges with two equivalent O(4)Mg2Fe2Co square pyramids. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1) and two equivalent Co(2) atoms. In the sixth O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Co(2), and two equivalent Co(1) atoms.