MgMn4CuO8 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(3), one O(4), and two equivalent O(5) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra, corners with four equivalent Mn(2)O6 octahedra,  an edgeedge with one Cu(1)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-70°. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(5) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Cu(1)O6 octahedra, corners with eight equivalent Mn(3)O6 octahedra, corners with three equivalent Mg(1)O4 tetrahedra,  a faceface with one Mn(2)O6 octahedra, and  a faceface with one Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-51°. In the second Mn site, Mn(2) is bonded to one O(3), one O(4), two equivalent O(2), and two equivalent O(5) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with four equivalent Mg(1)O4 tetrahedra, edges with two equivalent Cu(1)O6 octahedra, edges with four equivalent Mn(3)O6 octahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 48°. In the third Mn site, Mn(3) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra, edges with two equivalent Mn(2)O6 octahedra, edges with two equivalent Mn(3)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 43-51°. Cu(1) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(5) atoms to form CuO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, edges with four equivalent Mn(3)O6 octahedra,  an edgeedge with one Mg(1)O4 tetrahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 49°. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Mn(1), two equivalent Mn(3), and one Cu(1) atom to form distorted OMn3Cu tetrahedra that share  a cornercorner with one O(4)MgMn4 square pyramid, corners with two equivalent O(5)MgMn3Cu trigonal bipyramids, corners with two equivalent O(3)MgMn3 trigonal pyramids, corners with two equivalent O(2)Mn3Cu trigonal pyramids,  an edgeedge with one O(4)MgMn4 square pyramid, edges with two equivalent O(5)MgMn3Cu trigonal bipyramids, and edges with two equivalent O(2)Mn3Cu trigonal pyramids. In the second O site, O(2) is bonded to one Mn(1), one Mn(2), one Mn(3), and one Cu(1) atom to form OMn3Cu trigonal pyramids that share  a cornercorner with one O(4)MgMn4 square pyramid,  a cornercorner with one O(1)Mn3Cu tetrahedra, corners with five equivalent O(5)MgMn3Cu trigonal bipyramids,  a cornercorner with one O(2)Mn3Cu trigonal pyramid, corners with two equivalent O(3)MgMn3 trigonal pyramids,  an edgeedge with one O(4)MgMn4 square pyramid,  an edgeedge with one O(1)Mn3Cu tetrahedra,  an edgeedge with one O(5)MgMn3Cu trigonal bipyramid, and  an edgeedge with one O(2)Mn3Cu trigonal pyramid. In the third O site, O(3) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(3) atoms to form distorted OMgMn3 trigonal pyramids that share corners with four equivalent O(4)MgMn4 square pyramids, corners with two equivalent O(1)Mn3Cu tetrahedra, corners with two equivalent O(5)MgMn3Cu trigonal bipyramids, corners with four equivalent O(2)Mn3Cu trigonal pyramids, and edges with two equivalent O(5)MgMn3Cu trigonal bipyramids. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(1), one Mn(2), and two equivalent Mn(3) atoms to form distorted OMgMn4 square pyramids that share  a cornercorner with one O(1)Mn3Cu tetrahedra, corners with two equivalent O(2)Mn3Cu trigonal pyramids, corners with four equivalent O(3)MgMn3 trigonal pyramids,  an edgeedge with one O(1)Mn3Cu tetrahedra, edges with four equivalent O(5)MgMn3Cu trigonal bipyramids, and edges with two equivalent O(2)Mn3Cu trigonal pyramids. In the fifth O site, O(5) is bonded to one Mg(1), one Mn(1), one Mn(2), one Mn(3), and one Cu(1) atom to form distorted OMgMn3Cu trigonal bipyramids that share  a cornercorner with one O(1)Mn3Cu tetrahedra,  a cornercorner with one O(3)MgMn3 trigonal pyramid, corners with five equivalent O(2)Mn3Cu trigonal pyramids, edges with two equivalent O(4)MgMn4 square pyramids,  an edgeedge with one O(1)Mn3Cu tetrahedra, edges with two equivalent O(5)MgMn3Cu trigonal bipyramids,  an edgeedge with one O(3)MgMn3 trigonal pyramid, and  an edgeedge with one O(2)Mn3Cu trigonal pyramid. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mn(3) and one Cu(1) atom.
MgMn4CuO8 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(3), one O(4), and two equivalent O(5) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra, corners with four equivalent Mn(2)O6 octahedra,  an edgeedge with one Cu(1)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-70°. The Mg(1)-O(3) bond length is 1.92 Å. The Mg(1)-O(4) bond length is 2.04 Å. Both Mg(1)-O(5) bond lengths are 2.03 Å. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(5) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Cu(1)O6 octahedra, corners with eight equivalent Mn(3)O6 octahedra, corners with three equivalent Mg(1)O4 tetrahedra,  a faceface with one Mn(2)O6 octahedra, and  a faceface with one Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-51°. The Mn(1)-O(1) bond length is 2.32 Å. The Mn(1)-O(4) bond length is 2.38 Å. Both Mn(1)-O(2) bond lengths are 2.19 Å. Both Mn(1)-O(5) bond lengths are 2.20 Å. In the second Mn site, Mn(2) is bonded to one O(3), one O(4), two equivalent O(2), and two equivalent O(5) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with four equivalent Mg(1)O4 tetrahedra, edges with two equivalent Cu(1)O6 octahedra, edges with four equivalent Mn(3)O6 octahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 48°. The Mn(2)-O(3) bond length is 2.16 Å. The Mn(2)-O(4) bond length is 2.56 Å. Both Mn(2)-O(2) bond lengths are 1.94 Å. Both Mn(2)-O(5) bond lengths are 2.03 Å. In the third Mn site, Mn(3) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra, edges with two equivalent Mn(2)O6 octahedra, edges with two equivalent Mn(3)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 43-51°. The Mn(3)-O(1) bond length is 1.96 Å. The Mn(3)-O(2) bond length is 2.22 Å. The Mn(3)-O(3) bond length is 1.96 Å. The Mn(3)-O(4) bond length is 2.00 Å. The Mn(3)-O(5) bond length is 2.55 Å. The Mn(3)-O(6) bond length is 1.92 Å. Cu(1) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(5) atoms to form CuO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, edges with four equivalent Mn(3)O6 octahedra,  an edgeedge with one Mg(1)O4 tetrahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 49°. The Cu(1)-O(1) bond length is 2.19 Å. The Cu(1)-O(6) bond length is 1.98 Å. Both Cu(1)-O(2) bond lengths are 2.02 Å. Both Cu(1)-O(5) bond lengths are 2.04 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Mn(1), two equivalent Mn(3), and one Cu(1) atom to form distorted OMn3Cu tetrahedra that share  a cornercorner with one O(4)MgMn4 square pyramid, corners with two equivalent O(5)MgMn3Cu trigonal bipyramids, corners with two equivalent O(3)MgMn3 trigonal pyramids, corners with two equivalent O(2)Mn3Cu trigonal pyramids,  an edgeedge with one O(4)MgMn4 square pyramid, edges with two equivalent O(5)MgMn3Cu trigonal bipyramids, and edges with two equivalent O(2)Mn3Cu trigonal pyramids. In the second O site, O(2) is bonded to one Mn(1), one Mn(2), one Mn(3), and one Cu(1) atom to form OMn3Cu trigonal pyramids that share  a cornercorner with one O(4)MgMn4 square pyramid,  a cornercorner with one O(1)Mn3Cu tetrahedra, corners with five equivalent O(5)MgMn3Cu trigonal bipyramids,  a cornercorner with one O(2)Mn3Cu trigonal pyramid, corners with two equivalent O(3)MgMn3 trigonal pyramids,  an edgeedge with one O(4)MgMn4 square pyramid,  an edgeedge with one O(1)Mn3Cu tetrahedra,  an edgeedge with one O(5)MgMn3Cu trigonal bipyramid, and  an edgeedge with one O(2)Mn3Cu trigonal pyramid. In the third O site, O(3) is bonded to one Mg(1), one Mn(2), and two equivalent Mn(3) atoms to form distorted OMgMn3 trigonal pyramids that share corners with four equivalent O(4)MgMn4 square pyramids, corners with two equivalent O(1)Mn3Cu tetrahedra, corners with two equivalent O(5)MgMn3Cu trigonal bipyramids, corners with four equivalent O(2)Mn3Cu trigonal pyramids, and edges with two equivalent O(5)MgMn3Cu trigonal bipyramids. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(1), one Mn(2), and two equivalent Mn(3) atoms to form distorted OMgMn4 square pyramids that share  a cornercorner with one O(1)Mn3Cu tetrahedra, corners with two equivalent O(2)Mn3Cu trigonal pyramids, corners with four equivalent O(3)MgMn3 trigonal pyramids,  an edgeedge with one O(1)Mn3Cu tetrahedra, edges with four equivalent O(5)MgMn3Cu trigonal bipyramids, and edges with two equivalent O(2)Mn3Cu trigonal pyramids. In the fifth O site, O(5) is bonded to one Mg(1), one Mn(1), one Mn(2), one Mn(3), and one Cu(1) atom to form distorted OMgMn3Cu trigonal bipyramids that share  a cornercorner with one O(1)Mn3Cu tetrahedra,  a cornercorner with one O(3)MgMn3 trigonal pyramid, corners with five equivalent O(2)Mn3Cu trigonal pyramids, edges with two equivalent O(4)MgMn4 square pyramids,  an edgeedge with one O(1)Mn3Cu tetrahedra, edges with two equivalent O(5)MgMn3Cu trigonal bipyramids,  an edgeedge with one O(3)MgMn3 trigonal pyramid, and  an edgeedge with one O(2)Mn3Cu trigonal pyramid. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mn(3) and one Cu(1) atom.