MgCo5CuO8 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with six equivalent Co(3)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and edges with two equivalent Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-7°. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form CoO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and edges with two equivalent Cu(1)O6 octahedra. In the second Co site, Co(2) is bonded in a rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. In the third Co site, Co(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CoO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and edges with two equivalent Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-7°. In the fourth Co site, Co(4) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form CoO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and edges with two equivalent Cu(1)O6 octahedra. Cu(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form CuO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and edges with two equivalent Co(4)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Co(1), one Co(2), one Co(3), and one Cu(1) atom to form OMgCo3Cu square pyramids that share  a cornercorner with one O(3)MgCo3Cu square pyramid,  a cornercorner with one O(2)MgCo4 square pyramid, corners with four equivalent O(1)MgCo3Cu square pyramids, corners with three equivalent O(4)Co3Cu tetrahedra, edges with three equivalent O(3)MgCo3Cu square pyramids, edges with three equivalent O(2)MgCo4 square pyramids, and  an edgeedge with one O(4)Co3Cu tetrahedra. In the second O site, O(2) is bonded to one Mg(1), one Co(1), one Co(2), one Co(3), and one Co(4) atom to form OMgCo4 square pyramids that share  a cornercorner with one O(1)MgCo3Cu square pyramid,  a cornercorner with one O(3)MgCo3Cu square pyramid, corners with four equivalent O(2)MgCo4 square pyramids, corners with three equivalent O(4)Co3Cu tetrahedra, edges with three equivalent O(1)MgCo3Cu square pyramids, edges with three equivalent O(3)MgCo3Cu square pyramids, and  an edgeedge with one O(4)Co3Cu tetrahedra. In the third O site, O(3) is bonded to one Mg(1), one Co(2), one Co(3), one Co(4), and one Cu(1) atom to form OMgCo3Cu square pyramids that share  a cornercorner with one O(1)MgCo3Cu square pyramid,  a cornercorner with one O(2)MgCo4 square pyramid, corners with four equivalent O(3)MgCo3Cu square pyramids, corners with three equivalent O(4)Co3Cu tetrahedra, edges with three equivalent O(1)MgCo3Cu square pyramids, edges with three equivalent O(2)MgCo4 square pyramids, and  an edgeedge with one O(4)Co3Cu tetrahedra. In the fourth O site, O(4) is bonded to one Co(1), one Co(2), one Co(4), and one Cu(1) atom to form OCo3Cu tetrahedra that share corners with three equivalent O(1)MgCo3Cu square pyramids, corners with three equivalent O(3)MgCo3Cu square pyramids, corners with three equivalent O(2)MgCo4 square pyramids, corners with three equivalent O(4)Co3Cu tetrahedra,  an edgeedge with one O(1)MgCo3Cu square pyramid,  an edgeedge with one O(3)MgCo3Cu square pyramid, and  an edgeedge with one O(2)MgCo4 square pyramid.
MgCo5CuO8 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with six equivalent Co(3)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and edges with two equivalent Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-7°. Both Mg(1)-O(1) bond lengths are 2.13 Å. Both Mg(1)-O(2) bond lengths are 2.08 Å. Both Mg(1)-O(3) bond lengths are 2.11 Å. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form CoO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and edges with two equivalent Cu(1)O6 octahedra. Both Co(1)-O(1) bond lengths are 2.10 Å. Both Co(1)-O(2) bond lengths are 2.14 Å. Both Co(1)-O(4) bond lengths are 1.97 Å. In the second Co site, Co(2) is bonded in a rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Co(2)-O(1) bond length is 2.01 Å. The Co(2)-O(2) bond length is 2.04 Å. The Co(2)-O(3) bond length is 2.10 Å. The Co(2)-O(4) bond length is 1.88 Å. In the third Co site, Co(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CoO6 octahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(4)O6 octahedra, and edges with two equivalent Cu(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-7°. Both Co(3)-O(1) bond lengths are 2.17 Å. Both Co(3)-O(2) bond lengths are 2.10 Å. Both Co(3)-O(3) bond lengths are 2.27 Å. In the fourth Co site, Co(4) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form CoO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and edges with two equivalent Cu(1)O6 octahedra. Both Co(4)-O(2) bond lengths are 2.24 Å. Both Co(4)-O(3) bond lengths are 1.97 Å. Both Co(4)-O(4) bond lengths are 1.89 Å. Cu(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form CuO6 octahedra that share edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Co(1)O6 octahedra, edges with two equivalent Co(3)O6 octahedra, and edges with two equivalent Co(4)O6 octahedra. Both Cu(1)-O(1) bond lengths are 2.10 Å. Both Cu(1)-O(3) bond lengths are 2.19 Å. Both Cu(1)-O(4) bond lengths are 1.91 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Co(1), one Co(2), one Co(3), and one Cu(1) atom to form OMgCo3Cu square pyramids that share  a cornercorner with one O(3)MgCo3Cu square pyramid,  a cornercorner with one O(2)MgCo4 square pyramid, corners with four equivalent O(1)MgCo3Cu square pyramids, corners with three equivalent O(4)Co3Cu tetrahedra, edges with three equivalent O(3)MgCo3Cu square pyramids, edges with three equivalent O(2)MgCo4 square pyramids, and  an edgeedge with one O(4)Co3Cu tetrahedra. In the second O site, O(2) is bonded to one Mg(1), one Co(1), one Co(2), one Co(3), and one Co(4) atom to form OMgCo4 square pyramids that share  a cornercorner with one O(1)MgCo3Cu square pyramid,  a cornercorner with one O(3)MgCo3Cu square pyramid, corners with four equivalent O(2)MgCo4 square pyramids, corners with three equivalent O(4)Co3Cu tetrahedra, edges with three equivalent O(1)MgCo3Cu square pyramids, edges with three equivalent O(3)MgCo3Cu square pyramids, and  an edgeedge with one O(4)Co3Cu tetrahedra. In the third O site, O(3) is bonded to one Mg(1), one Co(2), one Co(3), one Co(4), and one Cu(1) atom to form OMgCo3Cu square pyramids that share  a cornercorner with one O(1)MgCo3Cu square pyramid,  a cornercorner with one O(2)MgCo4 square pyramid, corners with four equivalent O(3)MgCo3Cu square pyramids, corners with three equivalent O(4)Co3Cu tetrahedra, edges with three equivalent O(1)MgCo3Cu square pyramids, edges with three equivalent O(2)MgCo4 square pyramids, and  an edgeedge with one O(4)Co3Cu tetrahedra. In the fourth O site, O(4) is bonded to one Co(1), one Co(2), one Co(4), and one Cu(1) atom to form OCo3Cu tetrahedra that share corners with three equivalent O(1)MgCo3Cu square pyramids, corners with three equivalent O(3)MgCo3Cu square pyramids, corners with three equivalent O(2)MgCo4 square pyramids, corners with three equivalent O(4)Co3Cu tetrahedra,  an edgeedge with one O(1)MgCo3Cu square pyramid,  an edgeedge with one O(3)MgCo3Cu square pyramid, and  an edgeedge with one O(2)MgCo4 square pyramid.