MgFe5CuO8 is Aluminum carbonitride-derived structured and crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(5), one O(6), and two equivalent O(3) atoms to form distorted MgO4 tetrahedra that share corners with six equivalent Fe(2)O6 octahedra, corners with two equivalent Cu(1)O4 tetrahedra, and  an edgeedge with one Fe(4)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-58°. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 4-coordinate geometry to one O(5), one O(6), and two equivalent O(4) atoms. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cu(1)O4 tetrahedra,  a cornercorner with one Fe(4)O5 trigonal bipyramid, edges with two equivalent Fe(2)O6 octahedra, and  an edgeedge with one Fe(4)O5 trigonal bipyramid. In the third Fe site, Fe(3) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(3), and two equivalent O(4) atoms. In the fourth Fe site, Fe(4) is bonded to one O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted FeO5 trigonal bipyramids that share corners with two equivalent Fe(2)O6 octahedra, corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Fe(2)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 66°. Cu(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form CuO4 tetrahedra that share corners with six equivalent Fe(2)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, and corners with three equivalent Fe(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 55-69°. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Fe(3), two equivalent Fe(2), and one Cu(1) atom to form distorted OFe3Cu trigonal pyramids that share corners with four equivalent O(4)Fe4 tetrahedra, corners with two equivalent O(3)MgFe3Cu trigonal bipyramids, and edges with two equivalent O(3)MgFe3Cu trigonal bipyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Fe(4), two equivalent Fe(2), and one Cu(1) atom. In the third O site, O(3) is bonded to one Mg(1), one Fe(2), one Fe(3), one Fe(4), and one Cu(1) atom to form distorted OMgFe3Cu trigonal bipyramids that share corners with five equivalent O(4)Fe4 tetrahedra,  a cornercorner with one O(3)MgFe3Cu trigonal bipyramid,  a cornercorner with one O(1)Fe3Cu trigonal pyramid,  an edgeedge with one O(1)Fe3Cu trigonal pyramid, and  a faceface with one O(3)MgFe3Cu trigonal bipyramid. In the fourth O site, O(4) is bonded to one Fe(1), one Fe(2), one Fe(3), and one Fe(4) atom to form OFe4 tetrahedra that share  a cornercorner with one O(4)Fe4 tetrahedra, corners with five equivalent O(3)MgFe3Cu trigonal bipyramids, corners with two equivalent O(1)Fe3Cu trigonal pyramids, and  an edgeedge with one O(4)Fe4 tetrahedra. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms.
MgFe5CuO8 is Aluminum carbonitride-derived structured and crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(5), one O(6), and two equivalent O(3) atoms to form distorted MgO4 tetrahedra that share corners with six equivalent Fe(2)O6 octahedra, corners with two equivalent Cu(1)O4 tetrahedra, and  an edgeedge with one Fe(4)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-58°. The Mg(1)-O(5) bond length is 1.94 Å. The Mg(1)-O(6) bond length is 1.93 Å. Both Mg(1)-O(3) bond lengths are 2.07 Å. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 4-coordinate geometry to one O(5), one O(6), and two equivalent O(4) atoms. The Fe(1)-O(5) bond length is 2.40 Å. The Fe(1)-O(6) bond length is 2.24 Å. Both Fe(1)-O(4) bond lengths are 1.93 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cu(1)O4 tetrahedra,  a cornercorner with one Fe(4)O5 trigonal bipyramid, edges with two equivalent Fe(2)O6 octahedra, and  an edgeedge with one Fe(4)O5 trigonal bipyramid. The Fe(2)-O(1) bond length is 2.07 Å. The Fe(2)-O(2) bond length is 2.20 Å. The Fe(2)-O(3) bond length is 2.11 Å. The Fe(2)-O(4) bond length is 2.09 Å. The Fe(2)-O(5) bond length is 2.06 Å. The Fe(2)-O(6) bond length is 2.06 Å. In the third Fe site, Fe(3) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(3), and two equivalent O(4) atoms. The Fe(3)-O(1) bond length is 2.01 Å. Both Fe(3)-O(3) bond lengths are 2.22 Å. Both Fe(3)-O(4) bond lengths are 2.04 Å. In the fourth Fe site, Fe(4) is bonded to one O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted FeO5 trigonal bipyramids that share corners with two equivalent Fe(2)O6 octahedra, corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Fe(2)O6 octahedra, and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 66°. The Fe(4)-O(2) bond length is 1.91 Å. Both Fe(4)-O(3) bond lengths are 2.08 Å. Both Fe(4)-O(4) bond lengths are 2.00 Å. Cu(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form CuO4 tetrahedra that share corners with six equivalent Fe(2)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, and corners with three equivalent Fe(4)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 55-69°. The Cu(1)-O(1) bond length is 2.11 Å. The Cu(1)-O(2) bond length is 2.07 Å. Both Cu(1)-O(3) bond lengths are 2.11 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Fe(3), two equivalent Fe(2), and one Cu(1) atom to form distorted OFe3Cu trigonal pyramids that share corners with four equivalent O(4)Fe4 tetrahedra, corners with two equivalent O(3)MgFe3Cu trigonal bipyramids, and edges with two equivalent O(3)MgFe3Cu trigonal bipyramids. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Fe(4), two equivalent Fe(2), and one Cu(1) atom. In the third O site, O(3) is bonded to one Mg(1), one Fe(2), one Fe(3), one Fe(4), and one Cu(1) atom to form distorted OMgFe3Cu trigonal bipyramids that share corners with five equivalent O(4)Fe4 tetrahedra,  a cornercorner with one O(3)MgFe3Cu trigonal bipyramid,  a cornercorner with one O(1)Fe3Cu trigonal pyramid,  an edgeedge with one O(1)Fe3Cu trigonal pyramid, and  a faceface with one O(3)MgFe3Cu trigonal bipyramid. In the fourth O site, O(4) is bonded to one Fe(1), one Fe(2), one Fe(3), and one Fe(4) atom to form OFe4 tetrahedra that share  a cornercorner with one O(4)Fe4 tetrahedra, corners with five equivalent O(3)MgFe3Cu trigonal bipyramids, corners with two equivalent O(1)Fe3Cu trigonal pyramids, and  an edgeedge with one O(4)Fe4 tetrahedra. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), and two equivalent Fe(2) atoms.