MgMn2O4 crystallizes in the monoclinic P2_1/c space group. Mg(1) 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 two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(4), two equivalent O(2), and two equivalent O(3) atoms to form MnO5 trigonal bipyramids that share corners with four equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, and  an edgeedge with one Mn(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 51-64°. In the second Mn site, Mn(2) is bonded to one O(2), two equivalent O(4), and three equivalent O(1) atoms to form distorted MnO6 octahedra that share corners with four equivalent Mn(1)O5 trigonal bipyramids and edges with four equivalent Mn(2)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1) and three equivalent Mn(2) 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 corners with two equivalent O(3)Mg2Mn2 tetrahedra, corners with two equivalent O(2)MgMn3 trigonal pyramids, and edges with two equivalent O(3)Mg2Mn2 tetrahedra. In the third O site, O(3) is bonded to two equivalent Mg(1) and two equivalent Mn(1) atoms to form OMg2Mn2 tetrahedra that share corners with two equivalent O(3)Mg2Mn2 tetrahedra, corners with two equivalent O(2)MgMn3 trigonal pyramids,  an edgeedge with one O(3)Mg2Mn2 tetrahedra, and edges with two equivalent O(2)MgMn3 trigonal pyramids. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Mn(1), and two equivalent Mn(2) atoms.
MgMn2O4 crystallizes in the monoclinic P2_1/c space group. Mg(1) 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 Mg(1)-O(1) bond length is 2.08 Å. The Mg(1)-O(2) bond length is 2.26 Å. There is one shorter (2.05 Å) and one longer (2.12 Å) Mg(1)-O(3) bond length. There is one shorter (2.16 Å) and one longer (2.68 Å) Mg(1)-O(4) bond length. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(4), two equivalent O(2), and two equivalent O(3) atoms to form MnO5 trigonal bipyramids that share corners with four equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, and  an edgeedge with one Mn(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 51-64°. The Mn(1)-O(4) bond length is 1.94 Å. There is one shorter (1.97 Å) and one longer (2.10 Å) Mn(1)-O(2) bond length. There is one shorter (1.95 Å) and one longer (1.96 Å) Mn(1)-O(3) bond length. In the second Mn site, Mn(2) is bonded to one O(2), two equivalent O(4), and three equivalent O(1) atoms to form distorted MnO6 octahedra that share corners with four equivalent Mn(1)O5 trigonal bipyramids and edges with four equivalent Mn(2)O6 octahedra. The Mn(2)-O(2) bond length is 1.94 Å. There is one shorter (1.98 Å) and one longer (2.62 Å) Mn(2)-O(4) bond length. There are a spread of Mn(2)-O(1) bond distances ranging from 1.94-2.36 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1) and three equivalent Mn(2) 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 corners with two equivalent O(3)Mg2Mn2 tetrahedra, corners with two equivalent O(2)MgMn3 trigonal pyramids, and edges with two equivalent O(3)Mg2Mn2 tetrahedra. In the third O site, O(3) is bonded to two equivalent Mg(1) and two equivalent Mn(1) atoms to form OMg2Mn2 tetrahedra that share corners with two equivalent O(3)Mg2Mn2 tetrahedra, corners with two equivalent O(2)MgMn3 trigonal pyramids,  an edgeedge with one O(3)Mg2Mn2 tetrahedra, and edges with two equivalent O(2)MgMn3 trigonal pyramids. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Mn(1), and two equivalent Mn(2) atoms.