MgMn2O4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Mg(2)O6 octahedra, corners with four equivalent Mn(1)O5 trigonal bipyramids, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 44°. In the second Mg site, Mg(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 44°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Mg(2)O6 octahedra, corners with two equivalent Mg(1)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra,  an edgeedge with one Mg(2)O6 octahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 51-76°. In the second Mn site, Mn(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(2), one Mn(2), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form distorted OMgMn3 trigonal pyramids that share  a cornercorner with one O(2)MgMn3 trigonal pyramid, corners with two equivalent O(4)Mg2Mn2 trigonal pyramids, corners with four equivalent O(3)MgMn3 trigonal pyramids,  an edgeedge with one O(4)Mg2Mn2 trigonal pyramid, and  an edgeedge with one O(2)MgMn3 trigonal pyramid. In the third O site, O(3) is bonded to one Mg(2), one Mn(1), and two equivalent Mn(2) atoms to form distorted OMgMn3 trigonal pyramids that share corners with two equivalent O(4)Mg2Mn2 trigonal pyramids, corners with three equivalent O(3)MgMn3 trigonal pyramids, corners with four equivalent O(2)MgMn3 trigonal pyramids, and edges with two equivalent O(4)Mg2Mn2 trigonal pyramids. In the fourth O site, O(4) is bonded to one Mg(1), one Mg(2), and two equivalent Mn(2) atoms to form distorted OMg2Mn2 trigonal pyramids that share corners with two equivalent O(2)MgMn3 trigonal pyramids, corners with two equivalent O(3)MgMn3 trigonal pyramids, corners with four equivalent O(4)Mg2Mn2 trigonal pyramids,  an edgeedge with one O(2)MgMn3 trigonal pyramid, and edges with two equivalent O(3)MgMn3 trigonal pyramids.
MgMn2O4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Mg(2)O6 octahedra, corners with four equivalent Mn(1)O5 trigonal bipyramids, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 44°. Both Mg(1)-O(1) bond lengths are 2.20 Å. Both Mg(1)-O(2) bond lengths are 2.07 Å. Both Mg(1)-O(4) bond lengths are 2.13 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 44°. Both Mg(2)-O(1) bond lengths are 2.13 Å. Both Mg(2)-O(3) bond lengths are 2.13 Å. Both Mg(2)-O(4) bond lengths are 2.12 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Mg(2)O6 octahedra, corners with two equivalent Mg(1)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra,  an edgeedge with one Mg(2)O6 octahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 51-76°. The Mn(1)-O(3) bond length is 2.14 Å. Both Mn(1)-O(1) bond lengths are 1.98 Å. There is one shorter (1.94 Å) and one longer (2.00 Å) Mn(1)-O(2) bond length. In the second Mn site, Mn(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms. The Mn(2)-O(1) bond length is 2.69 Å. The Mn(2)-O(2) bond length is 2.16 Å. There is one shorter (1.97 Å) and one longer (1.98 Å) Mn(2)-O(3) bond length. There is one shorter (1.95 Å) and one longer (1.99 Å) Mn(2)-O(4) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(2), one Mn(2), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form distorted OMgMn3 trigonal pyramids that share  a cornercorner with one O(2)MgMn3 trigonal pyramid, corners with two equivalent O(4)Mg2Mn2 trigonal pyramids, corners with four equivalent O(3)MgMn3 trigonal pyramids,  an edgeedge with one O(4)Mg2Mn2 trigonal pyramid, and  an edgeedge with one O(2)MgMn3 trigonal pyramid. In the third O site, O(3) is bonded to one Mg(2), one Mn(1), and two equivalent Mn(2) atoms to form distorted OMgMn3 trigonal pyramids that share corners with two equivalent O(4)Mg2Mn2 trigonal pyramids, corners with three equivalent O(3)MgMn3 trigonal pyramids, corners with four equivalent O(2)MgMn3 trigonal pyramids, and edges with two equivalent O(4)Mg2Mn2 trigonal pyramids. In the fourth O site, O(4) is bonded to one Mg(1), one Mg(2), and two equivalent Mn(2) atoms to form distorted OMg2Mn2 trigonal pyramids that share corners with two equivalent O(2)MgMn3 trigonal pyramids, corners with two equivalent O(3)MgMn3 trigonal pyramids, corners with four equivalent O(4)Mg2Mn2 trigonal pyramids,  an edgeedge with one O(2)MgMn3 trigonal pyramid, and edges with two equivalent O(3)MgMn3 trigonal pyramids.