MgFe4(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 six equivalent Fe(3)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 6-7°. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O6 octahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form FeO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(3)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. In the third Fe site, Fe(3) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form FeO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 6-7°. Cu(1) is bonded in a distorted rectangular see-saw-like geometry to one O(2), one O(3), and two equivalent O(1) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(1), one Fe(2), one Fe(3), and one Cu(1) atom to form OMgFe3Cu trigonal bipyramids that share corners with three equivalent O(3)Fe3Cu tetrahedra,  a cornercorner with one O(2)MgFe3Cu trigonal bipyramid, corners with five equivalent O(1)MgFe3Cu trigonal bipyramids,  an edgeedge with one O(3)Fe3Cu tetrahedra, edges with three equivalent O(1)MgFe3Cu trigonal bipyramids, and edges with three equivalent O(2)MgFe3Cu trigonal bipyramids. In the second O site, O(2) is bonded to one Mg(1), one Fe(3), two equivalent Fe(1), and one Cu(1) atom to form OMgFe3Cu trigonal bipyramids that share corners with three equivalent O(3)Fe3Cu tetrahedra, corners with two equivalent O(1)MgFe3Cu trigonal bipyramids, corners with four equivalent O(2)MgFe3Cu trigonal bipyramids,  an edgeedge with one O(3)Fe3Cu tetrahedra, and edges with six equivalent O(1)MgFe3Cu trigonal bipyramids. In the third O site, O(3) is bonded to one Fe(2), two equivalent Fe(1), and one Cu(1) atom to form distorted OFe3Cu tetrahedra that share corners with three equivalent O(3)Fe3Cu tetrahedra, corners with three equivalent O(2)MgFe3Cu trigonal bipyramids, corners with six equivalent O(1)MgFe3Cu trigonal bipyramids,  an edgeedge with one O(2)MgFe3Cu trigonal bipyramid, and edges with two equivalent O(1)MgFe3Cu trigonal bipyramids.
MgFe4(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 six equivalent Fe(3)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 6-7°. Both Mg(1)-O(2) bond lengths are 2.13 Å. All Mg(1)-O(1) bond lengths are 2.13 Å. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form FeO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O6 octahedra. Both Fe(1)-O(1) bond lengths are 2.09 Å. Both Fe(1)-O(2) bond lengths are 2.09 Å. Both Fe(1)-O(3) bond lengths are 1.99 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form FeO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(3)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. Both Fe(2)-O(3) bond lengths are 1.99 Å. All Fe(2)-O(1) bond lengths are 2.09 Å. In the third Fe site, Fe(3) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form FeO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with four equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 6-7°. Both Fe(3)-O(2) bond lengths are 2.22 Å. All Fe(3)-O(1) bond lengths are 2.23 Å. Cu(1) is bonded in a distorted rectangular see-saw-like geometry to one O(2), one O(3), and two equivalent O(1) atoms. The Cu(1)-O(2) bond length is 2.17 Å. The Cu(1)-O(3) bond length is 1.86 Å. Both Cu(1)-O(1) bond lengths are 2.15 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(1), one Fe(2), one Fe(3), and one Cu(1) atom to form OMgFe3Cu trigonal bipyramids that share corners with three equivalent O(3)Fe3Cu tetrahedra,  a cornercorner with one O(2)MgFe3Cu trigonal bipyramid, corners with five equivalent O(1)MgFe3Cu trigonal bipyramids,  an edgeedge with one O(3)Fe3Cu tetrahedra, edges with three equivalent O(1)MgFe3Cu trigonal bipyramids, and edges with three equivalent O(2)MgFe3Cu trigonal bipyramids. In the second O site, O(2) is bonded to one Mg(1), one Fe(3), two equivalent Fe(1), and one Cu(1) atom to form OMgFe3Cu trigonal bipyramids that share corners with three equivalent O(3)Fe3Cu tetrahedra, corners with two equivalent O(1)MgFe3Cu trigonal bipyramids, corners with four equivalent O(2)MgFe3Cu trigonal bipyramids,  an edgeedge with one O(3)Fe3Cu tetrahedra, and edges with six equivalent O(1)MgFe3Cu trigonal bipyramids. In the third O site, O(3) is bonded to one Fe(2), two equivalent Fe(1), and one Cu(1) atom to form distorted OFe3Cu tetrahedra that share corners with three equivalent O(3)Fe3Cu tetrahedra, corners with three equivalent O(2)MgFe3Cu trigonal bipyramids, corners with six equivalent O(1)MgFe3Cu trigonal bipyramids,  an edgeedge with one O(2)MgFe3Cu trigonal bipyramid, and edges with two equivalent O(1)MgFe3Cu trigonal bipyramids.