Mg2Mn3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Mn(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra, and edges with three equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. In the second Mg site, Mg(2) is bonded to one O(4) and three equivalent O(2) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra and corners with nine equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-62°. Mn(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form MnO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with four equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1) and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), and two equivalent Mn(1) atoms to form distorted OMg2Mn2 tetrahedra that share corners with two equivalent O(2)Mg2Mn2 tetrahedra,  a cornercorner with one O(4)MgMn3 trigonal pyramid, edges with two equivalent O(2)Mg2Mn2 tetrahedra, and  an edgeedge with one O(4)MgMn3 trigonal pyramid. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded to one Mg(2) and three equivalent Mn(1) atoms to form a mixture of distorted corner and edge-sharing OMgMn3 trigonal pyramids.
Mg2Mn3O8 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Mn(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra, and edges with three equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. All Mg(1)-O(1) bond lengths are 2.05 Å. All Mg(1)-O(2) bond lengths are 2.10 Å. In the second Mg site, Mg(2) is bonded to one O(4) and three equivalent O(2) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(1)O6 octahedra and corners with nine equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-62°. The Mg(2)-O(4) bond length is 2.00 Å. All Mg(2)-O(2) bond lengths are 1.92 Å. Mn(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form MnO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with three equivalent Mg(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with four equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. The Mn(1)-O(3) bond length is 1.90 Å. The Mn(1)-O(4) bond length is 1.96 Å. Both Mn(1)-O(1) bond lengths are 1.86 Å. Both Mn(1)-O(2) bond lengths are 1.93 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1) and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), and two equivalent Mn(1) atoms to form distorted OMg2Mn2 tetrahedra that share corners with two equivalent O(2)Mg2Mn2 tetrahedra,  a cornercorner with one O(4)MgMn3 trigonal pyramid, edges with two equivalent O(2)Mg2Mn2 tetrahedra, and  an edgeedge with one O(4)MgMn3 trigonal pyramid. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded to one Mg(2) and three equivalent Mn(1) atoms to form a mixture of distorted corner and edge-sharing OMgMn3 trigonal pyramids.