Mg2Mn3O6 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with four equivalent Mn(2)O5 trigonal bipyramids, edges with four equivalent Mg(1)O6 octahedra, edges with three equivalent Mn(2)O5 trigonal bipyramids, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 40°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MnO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, corners with eight equivalent Mn(2)O5 trigonal bipyramids, edges with two equivalent Mn(1)O6 octahedra, and faces with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 40°. In the second Mn site, Mn(2) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted MnO5 trigonal bipyramids that share corners with four equivalent Mg(1)O6 octahedra, corners with four equivalent Mn(1)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, and edges with two equivalent Mn(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 6-75°. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with two equivalent O(3)Mg3Mn2 square pyramids, corners with four equivalent O(2)MgMn3 tetrahedra, corners with two equivalent O(1)Mg2Mn3 trigonal bipyramids, edges with three equivalent O(3)Mg3Mn2 square pyramids, edges with two equivalent O(2)MgMn3 tetrahedra, and edges with three equivalent O(1)Mg2Mn3 trigonal bipyramids. In the second O site, O(2) is bonded to one Mg(1), one Mn(1), and two equivalent Mn(2) atoms to form distorted OMgMn3 tetrahedra that share corners with five equivalent O(3)Mg3Mn2 square pyramids, corners with three equivalent O(2)MgMn3 tetrahedra, corners with four equivalent O(1)Mg2Mn3 trigonal bipyramids,  an edgeedge with one O(3)Mg3Mn2 square pyramid, and edges with two equivalent O(1)Mg2Mn3 trigonal bipyramids. In the third O site, O(3) is bonded to three equivalent Mg(1) and two equivalent Mn(2) atoms to form OMg3Mn2 square pyramids that share corners with five equivalent O(2)MgMn3 tetrahedra, corners with two equivalent O(1)Mg2Mn3 trigonal bipyramids, edges with four equivalent O(3)Mg3Mn2 square pyramids,  an edgeedge with one O(2)MgMn3 tetrahedra, and edges with three equivalent O(1)Mg2Mn3 trigonal bipyramids.
Mg2Mn3O6 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with four equivalent Mn(2)O5 trigonal bipyramids, edges with four equivalent Mg(1)O6 octahedra, edges with three equivalent Mn(2)O5 trigonal bipyramids, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 40°. The Mg(1)-O(2) bond length is 2.10 Å. Both Mg(1)-O(1) bond lengths are 2.08 Å. All Mg(1)-O(3) bond lengths are 2.13 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MnO6 octahedra that share corners with four equivalent Mg(1)O6 octahedra, corners with eight equivalent Mn(2)O5 trigonal bipyramids, edges with two equivalent Mn(1)O6 octahedra, and faces with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 40°. Both Mn(1)-O(2) bond lengths are 2.28 Å. All Mn(1)-O(1) bond lengths are 2.18 Å. In the second Mn site, Mn(2) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted MnO5 trigonal bipyramids that share corners with four equivalent Mg(1)O6 octahedra, corners with four equivalent Mn(1)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, and edges with two equivalent Mn(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 6-75°. The Mn(2)-O(1) bond length is 2.13 Å. Both Mn(2)-O(2) bond lengths are 1.95 Å. Both Mn(2)-O(3) bond lengths are 2.08 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Mg(1), one Mn(2), and two equivalent Mn(1) atoms to form distorted OMg2Mn3 trigonal bipyramids that share corners with two equivalent O(3)Mg3Mn2 square pyramids, corners with four equivalent O(2)MgMn3 tetrahedra, corners with two equivalent O(1)Mg2Mn3 trigonal bipyramids, edges with three equivalent O(3)Mg3Mn2 square pyramids, edges with two equivalent O(2)MgMn3 tetrahedra, and edges with three equivalent O(1)Mg2Mn3 trigonal bipyramids. In the second O site, O(2) is bonded to one Mg(1), one Mn(1), and two equivalent Mn(2) atoms to form distorted OMgMn3 tetrahedra that share corners with five equivalent O(3)Mg3Mn2 square pyramids, corners with three equivalent O(2)MgMn3 tetrahedra, corners with four equivalent O(1)Mg2Mn3 trigonal bipyramids,  an edgeedge with one O(3)Mg3Mn2 square pyramid, and edges with two equivalent O(1)Mg2Mn3 trigonal bipyramids. In the third O site, O(3) is bonded to three equivalent Mg(1) and two equivalent Mn(2) atoms to form OMg3Mn2 square pyramids that share corners with five equivalent O(2)MgMn3 tetrahedra, corners with two equivalent O(1)Mg2Mn3 trigonal bipyramids, edges with four equivalent O(3)Mg3Mn2 square pyramids,  an edgeedge with one O(2)MgMn3 tetrahedra, and edges with three equivalent O(1)Mg2Mn3 trigonal bipyramids.