MgMn4(CuO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with six equivalent Mn(2)O6 octahedra, edges with two equivalent Mn(3)O6 octahedra, and faces with two equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 15-51°. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra,  a faceface with one Mg(1)O6 octahedra,  a faceface with one Mn(2)O6 octahedra, and  a faceface with one Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-66°. In the second Mn site, Mn(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form distorted MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Mn(3)O6 octahedra, and faces with two equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 15-66°. In the third Mn site, Mn(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, and faces with two equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 39°. Cu(1) is bonded in a distorted square co-planar geometry to two equivalent O(2) and two equivalent O(3) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mn(2), one Mn(3), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mn(1), one Mn(2), and two equivalent Cu(1) atoms to form OMgMn2Cu2 trigonal bipyramids that share corners with three equivalent O(3)Mn2Cu2 tetrahedra, corners with four equivalent O(2)MgMn2Cu2 trigonal bipyramids, and  an edgeedge with one O(3)Mn2Cu2 tetrahedra. In the third O site, O(3) is bonded to one Mn(1), one Mn(3), and two equivalent Cu(1) atoms to form OMn2Cu2 tetrahedra that share corners with three equivalent O(3)Mn2Cu2 tetrahedra, corners with three equivalent O(2)MgMn2Cu2 trigonal bipyramids, and  an edgeedge with one O(2)MgMn2Cu2 trigonal bipyramid.
MgMn4(CuO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with six equivalent Mn(2)O6 octahedra, edges with two equivalent Mn(3)O6 octahedra, and faces with two equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 15-51°. Both Mg(1)-O(2) bond lengths are 2.20 Å. All Mg(1)-O(1) bond lengths are 2.16 Å. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra,  a faceface with one Mg(1)O6 octahedra,  a faceface with one Mn(2)O6 octahedra, and  a faceface with one Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-66°. The Mn(1)-O(2) bond length is 2.13 Å. The Mn(1)-O(3) bond length is 2.02 Å. There are two shorter (2.15 Å) and two longer (2.36 Å) Mn(1)-O(1) bond lengths. In the second Mn site, Mn(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form distorted MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra, corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Mn(3)O6 octahedra, and faces with two equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 15-66°. Both Mn(2)-O(2) bond lengths are 2.18 Å. All Mn(2)-O(1) bond lengths are 2.41 Å. In the third Mn site, Mn(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form MnO6 octahedra that share corners with four equivalent Mn(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mn(2)O6 octahedra, and faces with two equivalent Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 39°. Both Mn(3)-O(3) bond lengths are 1.96 Å. All Mn(3)-O(1) bond lengths are 2.05 Å. Cu(1) is bonded in a distorted square co-planar geometry to two equivalent O(2) and two equivalent O(3) atoms. Both Cu(1)-O(2) bond lengths are 2.01 Å. Both Cu(1)-O(3) bond lengths are 1.92 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mn(2), one Mn(3), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one Mg(1), one Mn(1), one Mn(2), and two equivalent Cu(1) atoms to form OMgMn2Cu2 trigonal bipyramids that share corners with three equivalent O(3)Mn2Cu2 tetrahedra, corners with four equivalent O(2)MgMn2Cu2 trigonal bipyramids, and  an edgeedge with one O(3)Mn2Cu2 tetrahedra. In the third O site, O(3) is bonded to one Mn(1), one Mn(3), and two equivalent Cu(1) atoms to form OMn2Cu2 tetrahedra that share corners with three equivalent O(3)Mn2Cu2 tetrahedra, corners with three equivalent O(2)MgMn2Cu2 trigonal bipyramids, and  an edgeedge with one O(2)MgMn2Cu2 trigonal bipyramid.