MgMn3CoO8 is beta indium sulfide-derived structured and crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(5), one O(6), and two equivalent O(4) atoms to form MgO4 tetrahedra that share corners with three equivalent Mn(2)O6 octahedra, corners with three equivalent Co(1)O6 octahedra, and corners with six equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-64°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MnO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Co(1)O6 octahedra. In the second Mn site, Mn(2) is bonded to one O(1), one O(6), two equivalent O(3), and two equivalent O(4) atoms to form distorted MnO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Mn(1)O6 octahedra. Co(1) is bonded to one O(2), one O(5), two equivalent O(3), and two equivalent O(4) atoms to form CoO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with four equivalent Mn(1)O6 octahedra. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mn(2) and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to two equivalent Mn(1) and one Co(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Mn(1), one Mn(2), and one Co(1) atom. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(1), one Mn(2), and one Co(1) atom to form distorted OMgMn2Co tetrahedra that share  a cornercorner with one O(4)MgMn2Co tetrahedra,  a cornercorner with one O(6)MgMn3 trigonal pyramid,  an edgeedge with one O(4)MgMn2Co tetrahedra, and  an edgeedge with one O(6)MgMn3 trigonal pyramid. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent Mn(1), and one Co(1) atom. In the sixth O site, O(6) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form a mixture of distorted edge and corner-sharing OMgMn3 trigonal pyramids.
MgMn3CoO8 is beta indium sulfide-derived structured and crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(5), one O(6), and two equivalent O(4) atoms to form MgO4 tetrahedra that share corners with three equivalent Mn(2)O6 octahedra, corners with three equivalent Co(1)O6 octahedra, and corners with six equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-64°. The Mg(1)-O(5) bond length is 2.05 Å. The Mg(1)-O(6) bond length is 1.95 Å. Both Mg(1)-O(4) bond lengths are 1.98 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MnO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Co(1)O6 octahedra. The Mn(1)-O(1) bond length is 1.89 Å. The Mn(1)-O(2) bond length is 1.93 Å. The Mn(1)-O(3) bond length is 1.91 Å. The Mn(1)-O(4) bond length is 1.99 Å. The Mn(1)-O(5) bond length is 2.00 Å. The Mn(1)-O(6) bond length is 1.97 Å. In the second Mn site, Mn(2) is bonded to one O(1), one O(6), two equivalent O(3), and two equivalent O(4) atoms to form distorted MnO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Co(1)O6 octahedra, and edges with four equivalent Mn(1)O6 octahedra. The Mn(2)-O(1) bond length is 2.23 Å. The Mn(2)-O(6) bond length is 2.20 Å. Both Mn(2)-O(3) bond lengths are 1.95 Å. Both Mn(2)-O(4) bond lengths are 1.98 Å. Co(1) is bonded to one O(2), one O(5), two equivalent O(3), and two equivalent O(4) atoms to form CoO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, edges with two equivalent Mn(2)O6 octahedra, and edges with four equivalent Mn(1)O6 octahedra. The Co(1)-O(2) bond length is 1.92 Å. The Co(1)-O(5) bond length is 1.99 Å. Both Co(1)-O(3) bond lengths are 1.93 Å. Both Co(1)-O(4) bond lengths are 1.98 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mn(2) and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to two equivalent Mn(1) and one Co(1) atom. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Mn(1), one Mn(2), and one Co(1) atom. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(1), one Mn(2), and one Co(1) atom to form distorted OMgMn2Co tetrahedra that share  a cornercorner with one O(4)MgMn2Co tetrahedra,  a cornercorner with one O(6)MgMn3 trigonal pyramid,  an edgeedge with one O(4)MgMn2Co tetrahedra, and  an edgeedge with one O(6)MgMn3 trigonal pyramid. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to one Mg(1), two equivalent Mn(1), and one Co(1) atom. In the sixth O site, O(6) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form a mixture of distorted edge and corner-sharing OMgMn3 trigonal pyramids.