MgFe4(CuO4)2 crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(3) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form edge-sharing FeO6 octahedra. In the second Fe site, Fe(2) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form distorted edge-sharing FeO6 octahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a distorted linear geometry to two equivalent O(2) and two equivalent O(4) atoms. In the second Cu site, Cu(2) is bonded in a distorted bent 150 degrees geometry to two equivalent O(1) and two equivalent O(2) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(2), two equivalent Fe(1), and one Cu(2) atom to form OMgFe3Cu trigonal bipyramids that share  a cornercorner with one O(1)MgFe3Cu trigonal bipyramid, corners with two equivalent O(3)MgFe3 trigonal pyramids, corners with five equivalent O(4)Fe3Cu trigonal pyramids, edges with two equivalent O(3)MgFe3 trigonal pyramids, and  a faceface with one O(1)MgFe3Cu trigonal bipyramid. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Fe(1), two equivalent Fe(2), one Cu(1), and one Cu(2) atom. In the third O site, O(3) is bonded to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms to form distorted OMgFe3 trigonal pyramids that share corners with two equivalent O(1)MgFe3Cu trigonal bipyramids,  a cornercorner with one O(3)MgFe3 trigonal pyramid, edges with two equivalent O(1)MgFe3Cu trigonal bipyramids,  an edgeedge with one O(3)MgFe3 trigonal pyramid, and edges with two equivalent O(4)Fe3Cu trigonal pyramids. In the fourth O site, O(4) is bonded to one Fe(2), two equivalent Fe(1), and one Cu(1) atom to form distorted OFe3Cu trigonal pyramids that share corners with five equivalent O(1)MgFe3Cu trigonal bipyramids,  a cornercorner with one O(4)Fe3Cu trigonal pyramid,  an edgeedge with one O(4)Fe3Cu trigonal pyramid, and edges with two equivalent O(3)MgFe3 trigonal pyramids.
MgFe4(CuO4)2 crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(3) atoms. Both Mg(1)-O(1) bond lengths are 2.20 Å. Both Mg(1)-O(3) bond lengths are 1.93 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form edge-sharing FeO6 octahedra. The Fe(1)-O(2) bond length is 1.94 Å. The Fe(1)-O(3) bond length is 2.17 Å. Both Fe(1)-O(1) bond lengths are 2.17 Å. Both Fe(1)-O(4) bond lengths are 1.99 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form distorted edge-sharing FeO6 octahedra. The Fe(2)-O(1) bond length is 2.16 Å. The Fe(2)-O(4) bond length is 2.34 Å. Both Fe(2)-O(2) bond lengths are 2.06 Å. Both Fe(2)-O(3) bond lengths are 2.04 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a distorted linear geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Cu(1)-O(2) bond lengths are 2.57 Å. Both Cu(1)-O(4) bond lengths are 1.80 Å. In the second Cu site, Cu(2) is bonded in a distorted bent 150 degrees geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Cu(2)-O(1) bond lengths are 1.88 Å. Both Cu(2)-O(2) bond lengths are 2.59 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(2), two equivalent Fe(1), and one Cu(2) atom to form OMgFe3Cu trigonal bipyramids that share  a cornercorner with one O(1)MgFe3Cu trigonal bipyramid, corners with two equivalent O(3)MgFe3 trigonal pyramids, corners with five equivalent O(4)Fe3Cu trigonal pyramids, edges with two equivalent O(3)MgFe3 trigonal pyramids, and  a faceface with one O(1)MgFe3Cu trigonal bipyramid. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Fe(1), two equivalent Fe(2), one Cu(1), and one Cu(2) atom. In the third O site, O(3) is bonded to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms to form distorted OMgFe3 trigonal pyramids that share corners with two equivalent O(1)MgFe3Cu trigonal bipyramids,  a cornercorner with one O(3)MgFe3 trigonal pyramid, edges with two equivalent O(1)MgFe3Cu trigonal bipyramids,  an edgeedge with one O(3)MgFe3 trigonal pyramid, and edges with two equivalent O(4)Fe3Cu trigonal pyramids. In the fourth O site, O(4) is bonded to one Fe(2), two equivalent Fe(1), and one Cu(1) atom to form distorted OFe3Cu trigonal pyramids that share corners with five equivalent O(1)MgFe3Cu trigonal bipyramids,  a cornercorner with one O(4)Fe3Cu trigonal pyramid,  an edgeedge with one O(4)Fe3Cu trigonal pyramid, and edges with two equivalent O(3)MgFe3 trigonal pyramids.