MgFe4(CuO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Cu(2)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-13°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(3), and two equivalent O(2) atoms. In the second Fe site, Fe(2) 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(2)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with two equivalent Cu(2)O6 octahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form CuO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(2)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. In the second Cu site, Cu(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form distorted CuO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-13°. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Fe(1), two equivalent Fe(2), and one Cu(1) atom to form OFe3Cu tetrahedra that share corners with six equivalent O(2)MgFe2Cu2 square pyramids, corners with three equivalent O(1)Fe3Cu tetrahedra, corners with three equivalent O(3)MgFe3Cu trigonal bipyramids, edges with two equivalent O(2)MgFe2Cu2 square pyramids, and  an edgeedge with one O(3)MgFe3Cu trigonal bipyramid. In the second O site, O(2) is bonded to one Mg(1), one Fe(1), one Fe(2), one Cu(1), and one Cu(2) atom to form distorted OMgFe2Cu2 square pyramids that share corners with five equivalent O(2)MgFe2Cu2 square pyramids, corners with three equivalent O(1)Fe3Cu tetrahedra,  a cornercorner with one O(3)MgFe3Cu trigonal bipyramid, edges with three equivalent O(2)MgFe2Cu2 square pyramids,  an edgeedge with one O(1)Fe3Cu tetrahedra, and edges with three equivalent O(3)MgFe3Cu trigonal bipyramids. In the third O site, O(3) is bonded to one Mg(1), one Fe(1), two equivalent Fe(2), and one Cu(2) atom to form distorted OMgFe3Cu trigonal bipyramids that share corners with two equivalent O(2)MgFe2Cu2 square pyramids, corners with three equivalent O(1)Fe3Cu tetrahedra, corners with four equivalent O(3)MgFe3Cu trigonal bipyramids, edges with six equivalent O(2)MgFe2Cu2 square pyramids, and  an edgeedge with one O(1)Fe3Cu tetrahedra.
MgFe4(CuO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Cu(2)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-13°. Both Mg(1)-O(3) bond lengths are 2.02 Å. All Mg(1)-O(2) bond lengths are 2.13 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(3), and two equivalent O(2) atoms. The Fe(1)-O(1) bond length is 1.93 Å. The Fe(1)-O(3) bond length is 2.10 Å. Both Fe(1)-O(2) bond lengths are 2.02 Å. In the second Fe site, Fe(2) 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(2)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with two equivalent Cu(2)O6 octahedra. Both Fe(2)-O(1) bond lengths are 2.00 Å. Both Fe(2)-O(2) bond lengths are 2.13 Å. Both Fe(2)-O(3) bond lengths are 2.10 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form CuO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(2)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. Both Cu(1)-O(1) bond lengths are 1.98 Å. All Cu(1)-O(2) bond lengths are 2.30 Å. In the second Cu site, Cu(2) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form distorted CuO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Cu(1)O6 octahedra, and edges with four equivalent Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 1-13°. Both Cu(2)-O(3) bond lengths are 2.57 Å. All Cu(2)-O(2) bond lengths are 2.14 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Fe(1), two equivalent Fe(2), and one Cu(1) atom to form OFe3Cu tetrahedra that share corners with six equivalent O(2)MgFe2Cu2 square pyramids, corners with three equivalent O(1)Fe3Cu tetrahedra, corners with three equivalent O(3)MgFe3Cu trigonal bipyramids, edges with two equivalent O(2)MgFe2Cu2 square pyramids, and  an edgeedge with one O(3)MgFe3Cu trigonal bipyramid. In the second O site, O(2) is bonded to one Mg(1), one Fe(1), one Fe(2), one Cu(1), and one Cu(2) atom to form distorted OMgFe2Cu2 square pyramids that share corners with five equivalent O(2)MgFe2Cu2 square pyramids, corners with three equivalent O(1)Fe3Cu tetrahedra,  a cornercorner with one O(3)MgFe3Cu trigonal bipyramid, edges with three equivalent O(2)MgFe2Cu2 square pyramids,  an edgeedge with one O(1)Fe3Cu tetrahedra, and edges with three equivalent O(3)MgFe3Cu trigonal bipyramids. In the third O site, O(3) is bonded to one Mg(1), one Fe(1), two equivalent Fe(2), and one Cu(2) atom to form distorted OMgFe3Cu trigonal bipyramids that share corners with two equivalent O(2)MgFe2Cu2 square pyramids, corners with three equivalent O(1)Fe3Cu tetrahedra, corners with four equivalent O(3)MgFe3Cu trigonal bipyramids, edges with six equivalent O(2)MgFe2Cu2 square pyramids, and  an edgeedge with one O(1)Fe3Cu tetrahedra.