MgMn4O8 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form MgO5 square pyramids that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(4)O6 octahedra,  an edgeedge with one Mn(4)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-55°. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(4)O6 octahedra, and edges with two equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 49-52°. In the second Mn site, Mn(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent Mn(2)O6 octahedra, edges with two equivalent Mn(3)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 49-54°. In the third Mn site, Mn(3) is bonded to one O(1), one O(6), two equivalent O(2), 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(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-52°. In the fourth Mn site, Mn(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(4)O6 octahedra, and  an edgeedge with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 51-54°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mn(3) and two equivalent Mn(4) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Mn(1) and two equivalent Mn(3) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Mn(4) and two equivalent Mn(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form OMgMn3 trigonal pyramids that share corners with two equivalent O(4)MgMn3 trigonal pyramids, edges with two equivalent O(7)Mg2Mn3 square pyramids, and edges with two equivalent O(6)Mg2Mn3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Mn(4) and two equivalent Mn(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Mg(1), one Mn(3), and two equivalent Mn(2) atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with two equivalent O(7)Mg2Mn3 square pyramids,  an edgeedge with one O(7)Mg2Mn3 square pyramid, edges with two equivalent O(6)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(4)MgMn3 trigonal pyramids. In the seventh O site, O(7) is bonded to two equivalent Mg(1), one Mn(1), and two equivalent Mn(4) atoms to form OMg2Mn3 square pyramids that share corners with two equivalent O(6)Mg2Mn3 trigonal bipyramids, edges with two equivalent O(7)Mg2Mn3 square pyramids,  an edgeedge with one O(6)Mg2Mn3 trigonal bipyramid, and edges with two equivalent O(4)MgMn3 trigonal pyramids. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one Mn(2) and two equivalent Mn(3) atoms.
MgMn4O8 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form MgO5 square pyramids that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(4)O6 octahedra,  an edgeedge with one Mn(4)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 4-55°. The Mg(1)-O(4) bond length is 2.13 Å. Both Mg(1)-O(6) bond lengths are 2.10 Å. Both Mg(1)-O(7) bond lengths are 2.06 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(4)O6 octahedra, and edges with two equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 49-52°. The Mn(1)-O(2) bond length is 1.96 Å. The Mn(1)-O(7) bond length is 2.22 Å. Both Mn(1)-O(4) bond lengths are 1.98 Å. Both Mn(1)-O(5) bond lengths are 1.95 Å. In the second Mn site, Mn(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent Mn(2)O6 octahedra, edges with two equivalent Mn(3)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 49-54°. The Mn(2)-O(4) bond length is 1.97 Å. The Mn(2)-O(8) bond length is 1.91 Å. Both Mn(2)-O(3) bond lengths are 1.92 Å. Both Mn(2)-O(6) bond lengths are 2.18 Å. In the third Mn site, Mn(3) is bonded to one O(1), one O(6), two equivalent O(2), 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(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-52°. The Mn(3)-O(1) bond length is 1.94 Å. The Mn(3)-O(6) bond length is 2.04 Å. Both Mn(3)-O(2) bond lengths are 1.95 Å. Both Mn(3)-O(8) bond lengths are 1.99 Å. In the fourth Mn site, Mn(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(4)O6 octahedra, and  an edgeedge with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 51-54°. The Mn(4)-O(3) bond length is 1.96 Å. The Mn(4)-O(5) bond length is 2.03 Å. Both Mn(4)-O(1) bond lengths are 1.93 Å. Both Mn(4)-O(7) bond lengths are 2.13 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mn(3) and two equivalent Mn(4) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Mn(1) and two equivalent Mn(3) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Mn(4) and two equivalent Mn(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form OMgMn3 trigonal pyramids that share corners with two equivalent O(4)MgMn3 trigonal pyramids, edges with two equivalent O(7)Mg2Mn3 square pyramids, and edges with two equivalent O(6)Mg2Mn3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Mn(4) and two equivalent Mn(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Mg(1), one Mn(3), and two equivalent Mn(2) atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with two equivalent O(7)Mg2Mn3 square pyramids,  an edgeedge with one O(7)Mg2Mn3 square pyramid, edges with two equivalent O(6)Mg2Mn3 trigonal bipyramids, and edges with two equivalent O(4)MgMn3 trigonal pyramids. In the seventh O site, O(7) is bonded to two equivalent Mg(1), one Mn(1), and two equivalent Mn(4) atoms to form OMg2Mn3 square pyramids that share corners with two equivalent O(6)Mg2Mn3 trigonal bipyramids, edges with two equivalent O(7)Mg2Mn3 square pyramids,  an edgeedge with one O(6)Mg2Mn3 trigonal bipyramid, and edges with two equivalent O(4)MgMn3 trigonal pyramids. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one Mn(2) and two equivalent Mn(3) atoms.