MgMn4(CuO4)2 crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded to two equivalent O(2) and two equivalent O(4) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Mn(1)O4 tetrahedra,  an edgeedge with one Mn(2)O4 tetrahedra, and edges with two equivalent Mn(3)O5 trigonal bipyramids. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form MnO4 tetrahedra that share corners with two equivalent Mg(1)O4 tetrahedra and corners with six equivalent Mn(3)O5 trigonal bipyramids. In the second Mn site, Mn(2) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form distorted MnO4 tetrahedra that share corners with four equivalent Mn(3)O5 trigonal bipyramids and  an edgeedge with one Mg(1)O4 tetrahedra. In the third Mn site, Mn(3) is bonded to one O(3), two equivalent O(1), and two equivalent O(4) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mn(2)O4 tetrahedra, corners with three equivalent Mn(1)O4 tetrahedra,  an edgeedge with one Mg(1)O4 tetrahedra, and edges with two equivalent Mn(3)O5 trigonal bipyramids. Cu(1) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(3) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mn(2) and two equivalent Mn(3) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(2), and two equivalent Cu(1) atoms. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mn(1), one Mn(3), and two equivalent Cu(1) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(1), and two equivalent Mn(3) atoms to form a mixture of corner and face-sharing OMgMn3 trigonal pyramids.
MgMn4(CuO4)2 crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded to two equivalent O(2) and two equivalent O(4) atoms to form distorted MgO4 tetrahedra that share corners with two equivalent Mn(1)O4 tetrahedra,  an edgeedge with one Mn(2)O4 tetrahedra, and edges with two equivalent Mn(3)O5 trigonal bipyramids. Both Mg(1)-O(2) bond lengths are 1.93 Å. Both Mg(1)-O(4) bond lengths are 2.01 Å. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form MnO4 tetrahedra that share corners with two equivalent Mg(1)O4 tetrahedra and corners with six equivalent Mn(3)O5 trigonal bipyramids. Both Mn(1)-O(3) bond lengths are 2.09 Å. Both Mn(1)-O(4) bond lengths are 2.13 Å. In the second Mn site, Mn(2) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form distorted MnO4 tetrahedra that share corners with four equivalent Mn(3)O5 trigonal bipyramids and  an edgeedge with one Mg(1)O4 tetrahedra. Both Mn(2)-O(1) bond lengths are 1.96 Å. Both Mn(2)-O(2) bond lengths are 2.12 Å. In the third Mn site, Mn(3) is bonded to one O(3), two equivalent O(1), and two equivalent O(4) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Mn(2)O4 tetrahedra, corners with three equivalent Mn(1)O4 tetrahedra,  an edgeedge with one Mg(1)O4 tetrahedra, and edges with two equivalent Mn(3)O5 trigonal bipyramids. The Mn(3)-O(3) bond length is 2.16 Å. Both Mn(3)-O(1) bond lengths are 1.92 Å. Both Mn(3)-O(4) bond lengths are 2.05 Å. Cu(1) is bonded in a square co-planar geometry to two equivalent O(2) and two equivalent O(3) atoms. Both Cu(1)-O(2) bond lengths are 2.00 Å. Both Cu(1)-O(3) bond lengths are 2.01 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mn(2) and two equivalent Mn(3) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(2), and two equivalent Cu(1) atoms. In the third O site, O(3) is bonded in a rectangular see-saw-like geometry to one Mn(1), one Mn(3), and two equivalent Cu(1) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Mn(1), and two equivalent Mn(3) atoms to form a mixture of corner and face-sharing OMgMn3 trigonal pyramids.