MgMn4O8 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(5), one O(6), one O(7), and one O(8) atom to form MgO5 square pyramids that share  a cornercorner with one Mn(4)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, corners with three equivalent Mn(3)O6 octahedra,  an edgeedge with one Mn(2)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra, and  a faceface with one Mn(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 13-53°. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(4)O6 octahedra,  an edgeedge with one Mn(1)O6 octahedra, edges with three equivalent Mn(2)O6 octahedra, and edges with two equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 48-56°. In the second Mn site, Mn(2) is bonded to one O(1), one O(2), one O(4), one O(6), and two equivalent O(5) atoms to form MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids,  an edgeedge with one Mn(2)O6 octahedra, edges with three equivalent Mn(1)O6 octahedra, and  an edgeedge with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 49-56°. In the third Mn site, Mn(3) is bonded to one O(2), one O(3), one O(4), one O(8), and two equivalent O(7) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, corners with three equivalent Mg(1)O5 square pyramids,  an edgeedge with one Mn(3)O6 octahedra, and edges with three equivalent Mn(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-56°. In the fourth Mn site, Mn(4) is bonded to one O(1), one O(3), one O(4), one O(7), and two equivalent O(8) atoms to form MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra,  a cornercorner with one Mg(1)O5 square pyramid,  an edgeedge with one Mn(4)O6 octahedra, edges with three equivalent Mn(3)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 48-56°. There are eight inequivalent O sites. In the first O site, O(5) is bonded to one Mg(1), one Mn(1), and two equivalent Mn(2) atoms to form a mixture of distorted edge and corner-sharing OMgMn3 trigonal pyramids. In the second O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms. In the third O site, O(7) is bonded to one Mg(1), one Mn(4), and two equivalent Mn(3) atoms to form a mixture of edge and corner-sharing OMgMn3 trigonal pyramids. In the fourth O site, O(8) is bonded to one Mg(1), one Mn(3), and two equivalent Mn(4) atoms to form a mixture of edge and corner-sharing OMgMn3 trigonal pyramids. In the fifth O site, O(1) is bonded to one Mg(1), one Mn(1), one Mn(2), and one Mn(4) atom to form a mixture of edge and corner-sharing OMgMn3 trigonal pyramids. In the sixth O site, O(2) is bonded in a trigonal planar geometry to one Mn(1), one Mn(2), and one Mn(3) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(3), and one Mn(4) atom. In the eighth O site, O(4) is bonded in a trigonal planar geometry to one Mn(2), one Mn(3), and one Mn(4) atom.
MgMn4O8 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(5), one O(6), one O(7), and one O(8) atom to form MgO5 square pyramids that share  a cornercorner with one Mn(4)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, corners with three equivalent Mn(3)O6 octahedra,  an edgeedge with one Mn(2)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra, and  a faceface with one Mn(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 13-53°. The Mg(1)-O(1) bond length is 2.13 Å. The Mg(1)-O(5) bond length is 2.04 Å. The Mg(1)-O(6) bond length is 2.09 Å. The Mg(1)-O(7) bond length is 2.13 Å. The Mg(1)-O(8) bond length is 2.03 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(6) atoms to form MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(4)O6 octahedra,  an edgeedge with one Mn(1)O6 octahedra, edges with three equivalent Mn(2)O6 octahedra, and edges with two equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 48-56°. The Mn(1)-O(1) bond length is 1.94 Å. The Mn(1)-O(2) bond length is 1.90 Å. The Mn(1)-O(3) bond length is 1.90 Å. The Mn(1)-O(5) bond length is 1.94 Å. There is one shorter (1.99 Å) and one longer (2.07 Å) Mn(1)-O(6) bond length. In the second Mn site, Mn(2) is bonded to one O(1), one O(2), one O(4), one O(6), and two equivalent O(5) atoms to form MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids,  an edgeedge with one Mn(2)O6 octahedra, edges with three equivalent Mn(1)O6 octahedra, and  an edgeedge with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 49-56°. The Mn(2)-O(1) bond length is 2.10 Å. The Mn(2)-O(2) bond length is 1.99 Å. The Mn(2)-O(4) bond length is 1.92 Å. The Mn(2)-O(6) bond length is 2.05 Å. There is one shorter (2.00 Å) and one longer (2.18 Å) Mn(2)-O(5) bond length. In the third Mn site, Mn(3) is bonded to one O(2), one O(3), one O(4), one O(8), and two equivalent O(7) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, corners with three equivalent Mg(1)O5 square pyramids,  an edgeedge with one Mn(3)O6 octahedra, and edges with three equivalent Mn(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-56°. The Mn(3)-O(2) bond length is 1.93 Å. The Mn(3)-O(3) bond length is 2.12 Å. The Mn(3)-O(4) bond length is 1.98 Å. The Mn(3)-O(8) bond length is 2.24 Å. There is one shorter (2.01 Å) and one longer (2.02 Å) Mn(3)-O(7) bond length. In the fourth Mn site, Mn(4) is bonded to one O(1), one O(3), one O(4), one O(7), and two equivalent O(8) atoms to form MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra,  a cornercorner with one Mg(1)O5 square pyramid,  an edgeedge with one Mn(4)O6 octahedra, edges with three equivalent Mn(3)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 48-56°. The Mn(4)-O(1) bond length is 1.97 Å. The Mn(4)-O(3) bond length is 1.91 Å. The Mn(4)-O(4) bond length is 1.90 Å. The Mn(4)-O(7) bond length is 2.02 Å. There is one shorter (1.94 Å) and one longer (2.01 Å) Mn(4)-O(8) bond length. There are eight inequivalent O sites. In the first O site, O(5) is bonded to one Mg(1), one Mn(1), and two equivalent Mn(2) atoms to form a mixture of distorted edge and corner-sharing OMgMn3 trigonal pyramids. In the second O site, O(6) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms. In the third O site, O(7) is bonded to one Mg(1), one Mn(4), and two equivalent Mn(3) atoms to form a mixture of edge and corner-sharing OMgMn3 trigonal pyramids. In the fourth O site, O(8) is bonded to one Mg(1), one Mn(3), and two equivalent Mn(4) atoms to form a mixture of edge and corner-sharing OMgMn3 trigonal pyramids. In the fifth O site, O(1) is bonded to one Mg(1), one Mn(1), one Mn(2), and one Mn(4) atom to form a mixture of edge and corner-sharing OMgMn3 trigonal pyramids. In the sixth O site, O(2) is bonded in a trigonal planar geometry to one Mn(1), one Mn(2), and one Mn(3) atom. In the seventh O site, O(3) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(3), and one Mn(4) atom. In the eighth O site, O(4) is bonded in a trigonal planar geometry to one Mn(2), one Mn(3), and one Mn(4) atom.