MgCu2O4 crystallizes in the monoclinic Cm space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(6), and two equivalent O(7) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(5), and two equivalent O(8) atoms. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form CuO5 square pyramids that share corners with two equivalent Cu(2)O6 octahedra, corners with two equivalent Cu(3)O6 octahedra, and edges with two equivalent Cu(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 49-59°. In the second Cu site, Cu(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form CuO6 octahedra that share corners with two equivalent Cu(1)O5 square pyramids, corners with two equivalent Cu(4)O5 square pyramids, edges with two equivalent Cu(2)O6 octahedra, and edges with two equivalent Cu(3)O6 octahedra. In the third Cu site, Cu(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form distorted CuO6 octahedra that share corners with two equivalent Cu(1)O5 square pyramids, corners with two equivalent Cu(4)O5 square pyramids, edges with two equivalent Cu(2)O6 octahedra, and edges with two equivalent Cu(3)O6 octahedra. In the fourth Cu site, Cu(4) is bonded to one O(3), two equivalent O(1), and two equivalent O(7) atoms to form CuO5 square pyramids that share corners with two equivalent Cu(2)O6 octahedra, corners with two equivalent Cu(3)O6 octahedra, and edges with two equivalent Cu(4)O5 square pyramids. The corner-sharing octahedral tilt angles range from 49-56°. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Cu(3), and two equivalent Cu(4) atoms to form distorted OMgCu3 trigonal pyramids that share  a cornercorner with one O(6)Mg2Cu3 trigonal bipyramid, corners with two equivalent O(1)MgCu3 trigonal pyramids, and edges with two equivalent O(8)Mg2Cu3 trigonal bipyramids. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Cu(1) and two equivalent Cu(3) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Cu(4) and two equivalent Cu(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Cu(2), and two equivalent Cu(1) atoms to form distorted OMgCu3 trigonal pyramids that share  a cornercorner with one O(8)Mg2Cu3 trigonal bipyramid, corners with two equivalent O(4)MgCu3 trigonal pyramids, and edges with two equivalent O(6)Mg2Cu3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(2) and two equivalent Cu(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Mg(1), one Cu(3), and two equivalent Cu(2) atoms to form distorted OMg2Cu3 trigonal bipyramids that share  a cornercorner with one O(1)MgCu3 trigonal pyramid, edges with two equivalent O(6)Mg2Cu3 trigonal bipyramids, edges with two equivalent O(8)Mg2Cu3 trigonal bipyramids, and edges with two equivalent O(4)MgCu3 trigonal pyramids. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1) and two equivalent Cu(4) atoms. In the eighth O site, O(8) is bonded to two equivalent Mg(2), one Cu(2), and two equivalent Cu(3) atoms to form distorted OMg2Cu3 trigonal bipyramids that share  a cornercorner with one O(4)MgCu3 trigonal pyramid, edges with two equivalent O(6)Mg2Cu3 trigonal bipyramids, edges with two equivalent O(8)Mg2Cu3 trigonal bipyramids, and edges with two equivalent O(1)MgCu3 trigonal pyramids.
MgCu2O4 crystallizes in the monoclinic Cm space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(6), and two equivalent O(7) atoms. The Mg(1)-O(4) bond length is 2.21 Å. Both Mg(1)-O(6) bond lengths are 2.00 Å. Both Mg(1)-O(7) bond lengths are 2.02 Å. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(5), and two equivalent O(8) atoms. The Mg(2)-O(1) bond length is 2.21 Å. Both Mg(2)-O(5) bond lengths are 2.02 Å. Both Mg(2)-O(8) bond lengths are 2.00 Å. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form CuO5 square pyramids that share corners with two equivalent Cu(2)O6 octahedra, corners with two equivalent Cu(3)O6 octahedra, and edges with two equivalent Cu(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 49-59°. The Cu(1)-O(2) bond length is 2.07 Å. Both Cu(1)-O(4) bond lengths are 1.94 Å. Both Cu(1)-O(5) bond lengths are 1.95 Å. In the second Cu site, Cu(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form CuO6 octahedra that share corners with two equivalent Cu(1)O5 square pyramids, corners with two equivalent Cu(4)O5 square pyramids, edges with two equivalent Cu(2)O6 octahedra, and edges with two equivalent Cu(3)O6 octahedra. The Cu(2)-O(4) bond length is 1.95 Å. The Cu(2)-O(8) bond length is 2.04 Å. Both Cu(2)-O(3) bond lengths are 1.90 Å. Both Cu(2)-O(6) bond lengths are 2.10 Å. In the third Cu site, Cu(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form distorted CuO6 octahedra that share corners with two equivalent Cu(1)O5 square pyramids, corners with two equivalent Cu(4)O5 square pyramids, edges with two equivalent Cu(2)O6 octahedra, and edges with two equivalent Cu(3)O6 octahedra. The Cu(3)-O(1) bond length is 1.95 Å. The Cu(3)-O(6) bond length is 2.04 Å. Both Cu(3)-O(2) bond lengths are 1.89 Å. Both Cu(3)-O(8) bond lengths are 2.10 Å. In the fourth Cu site, Cu(4) is bonded to one O(3), two equivalent O(1), and two equivalent O(7) atoms to form CuO5 square pyramids that share corners with two equivalent Cu(2)O6 octahedra, corners with two equivalent Cu(3)O6 octahedra, and edges with two equivalent Cu(4)O5 square pyramids. The corner-sharing octahedral tilt angles range from 49-56°. The Cu(4)-O(3) bond length is 1.99 Å. Both Cu(4)-O(1) bond lengths are 1.94 Å. Both Cu(4)-O(7) bond lengths are 1.95 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Cu(3), and two equivalent Cu(4) atoms to form distorted OMgCu3 trigonal pyramids that share  a cornercorner with one O(6)Mg2Cu3 trigonal bipyramid, corners with two equivalent O(1)MgCu3 trigonal pyramids, and edges with two equivalent O(8)Mg2Cu3 trigonal bipyramids. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Cu(1) and two equivalent Cu(3) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Cu(4) and two equivalent Cu(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Cu(2), and two equivalent Cu(1) atoms to form distorted OMgCu3 trigonal pyramids that share  a cornercorner with one O(8)Mg2Cu3 trigonal bipyramid, corners with two equivalent O(4)MgCu3 trigonal pyramids, and edges with two equivalent O(6)Mg2Cu3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(2) and two equivalent Cu(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Mg(1), one Cu(3), and two equivalent Cu(2) atoms to form distorted OMg2Cu3 trigonal bipyramids that share  a cornercorner with one O(1)MgCu3 trigonal pyramid, edges with two equivalent O(6)Mg2Cu3 trigonal bipyramids, edges with two equivalent O(8)Mg2Cu3 trigonal bipyramids, and edges with two equivalent O(4)MgCu3 trigonal pyramids. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1) and two equivalent Cu(4) atoms. In the eighth O site, O(8) is bonded to two equivalent Mg(2), one Cu(2), and two equivalent Cu(3) atoms to form distorted OMg2Cu3 trigonal bipyramids that share  a cornercorner with one O(4)MgCu3 trigonal pyramid, edges with two equivalent O(6)Mg2Cu3 trigonal bipyramids, edges with two equivalent O(8)Mg2Cu3 trigonal bipyramids, and edges with two equivalent O(1)MgCu3 trigonal pyramids.