MgCu2O4 is Spinel-like structured and crystallizes in the trigonal R3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(3) and three equivalent O(4) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra and corners with nine equivalent Cu(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-60°. In the second Mg site, Mg(2) is bonded to three equivalent O(1) and three equivalent O(4) atoms to form MgO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cu(1)O4 tetrahedra, and edges with six equivalent Cu(2)O6 octahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(2) and three equivalent O(1) atoms to form CuO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra and corners with nine equivalent Cu(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-61°. In the second Cu site, Cu(2) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form CuO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with four equivalent Cu(2)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Cu(1), and two equivalent Cu(2) atoms to form distorted OMgCu3 trigonal pyramids that share corners with two equivalent O(1)MgCu3 trigonal pyramids, corners with seven equivalent O(4)Mg2Cu2 trigonal pyramids, and edges with two equivalent O(1)MgCu3 trigonal pyramids. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Cu(1) and three equivalent Cu(2) atoms. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1) and three equivalent Cu(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Mg(2), and two equivalent Cu(2) atoms to form distorted OMg2Cu2 trigonal pyramids that share corners with two equivalent O(4)Mg2Cu2 trigonal pyramids, corners with seven equivalent O(1)MgCu3 trigonal pyramids, and edges with two equivalent O(4)Mg2Cu2 trigonal pyramids.
MgCu2O4 is Spinel-like structured and crystallizes in the trigonal R3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(3) and three equivalent O(4) atoms to form MgO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra and corners with nine equivalent Cu(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-60°. The Mg(1)-O(3) bond length is 1.99 Å. All Mg(1)-O(4) bond lengths are 1.98 Å. In the second Mg site, Mg(2) is bonded to three equivalent O(1) and three equivalent O(4) atoms to form MgO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cu(1)O4 tetrahedra, and edges with six equivalent Cu(2)O6 octahedra. All Mg(2)-O(1) bond lengths are 2.09 Å. All Mg(2)-O(4) bond lengths are 2.05 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(2) and three equivalent O(1) atoms to form CuO4 tetrahedra that share corners with three equivalent Mg(2)O6 octahedra and corners with nine equivalent Cu(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 55-61°. The Cu(1)-O(2) bond length is 1.89 Å. All Cu(1)-O(1) bond lengths are 1.98 Å. In the second Cu site, Cu(2) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form CuO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Mg(2)O6 octahedra, and edges with four equivalent Cu(2)O6 octahedra. The Cu(2)-O(2) bond length is 2.10 Å. The Cu(2)-O(3) bond length is 2.08 Å. Both Cu(2)-O(1) bond lengths are 1.96 Å. Both Cu(2)-O(4) bond lengths are 1.95 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Cu(1), and two equivalent Cu(2) atoms to form distorted OMgCu3 trigonal pyramids that share corners with two equivalent O(1)MgCu3 trigonal pyramids, corners with seven equivalent O(4)Mg2Cu2 trigonal pyramids, and edges with two equivalent O(1)MgCu3 trigonal pyramids. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Cu(1) and three equivalent Cu(2) atoms. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1) and three equivalent Cu(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Mg(2), and two equivalent Cu(2) atoms to form distorted OMg2Cu2 trigonal pyramids that share corners with two equivalent O(4)Mg2Cu2 trigonal pyramids, corners with seven equivalent O(1)MgCu3 trigonal pyramids, and edges with two equivalent O(4)Mg2Cu2 trigonal pyramids.