CuOMgO crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted see-saw-like geometry to one O(4), one O(6), and two equivalent O(7) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one O(1), one O(8), and two equivalent O(5) atoms. In the third Mg site, Mg(3) is bonded to one O(7), one O(8), and two equivalent O(3) atoms to form MgO4 tetrahedra that share corners with two equivalent Mg(3)O4 tetrahedra and  a cornercorner with one Mg(4)O5 trigonal bipyramid. In the fourth Mg site, Mg(4) is bonded to one O(5), one O(6), one O(7), and two equivalent O(2) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Mg(3)O4 tetrahedra,  a cornercorner with one Cu(1)O4 tetrahedra, corners with two equivalent Mg(4)O5 trigonal bipyramids, and  an edgeedge with one Cu(1)O4 tetrahedra. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(2), one O(5), and two equivalent O(4) atoms to form distorted CuO4 tetrahedra that share corners with two equivalent Cu(1)O4 tetrahedra,  a cornercorner with one Mg(4)O5 trigonal bipyramid, and  an edgeedge with one Mg(4)O5 trigonal bipyramid. In the second Cu site, Cu(2) is bonded in a rectangular see-saw-like geometry to one O(3), one O(4), one O(6), and one O(8) atom. In the third Cu site, Cu(3) is bonded in a rectangular see-saw-like geometry to one O(1), one O(2), one O(6), and one O(8) atom. In the fourth Cu site, Cu(4) is bonded in a trigonal planar geometry to one O(3) and two equivalent O(1) atoms. 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 OMgCu3 tetrahedra that share  a cornercorner with one O(2)Mg2Cu2 tetrahedra, corners with two equivalent O(3)Mg2Cu2 tetrahedra, corners with two equivalent O(5)Mg3Cu tetrahedra, and corners with two equivalent O(1)MgCu3 tetrahedra. In the second O site, O(2) is bonded to two equivalent Mg(4), one Cu(1), and one Cu(3) atom to form distorted OMg2Cu2 tetrahedra that share  a cornercorner with one O(5)Mg3Cu tetrahedra,  a cornercorner with one O(1)MgCu3 tetrahedra, corners with two equivalent O(2)Mg2Cu2 tetrahedra, and  an edgeedge with one O(5)Mg3Cu tetrahedra. In the third O site, O(3) is bonded to two equivalent Mg(3), one Cu(2), and one Cu(4) atom to form OMg2Cu2 tetrahedra that share corners with two equivalent O(3)Mg2Cu2 tetrahedra and corners with two equivalent O(1)MgCu3 tetrahedra. In the fourth O site, O(4) is bonded in a distorted see-saw-like geometry to one Mg(1), one Cu(2), and two equivalent Cu(1) atoms. In the fifth O site, O(5) is bonded to one Mg(4), two equivalent Mg(2), and one Cu(1) atom to form distorted OMg3Cu tetrahedra that share  a cornercorner with one O(2)Mg2Cu2 tetrahedra, corners with two equivalent O(5)Mg3Cu tetrahedra, corners with two equivalent O(1)MgCu3 tetrahedra, and  an edgeedge with one O(2)Mg2Cu2 tetrahedra. In the sixth O site, O(6) is bonded in a distorted see-saw-like geometry to one Mg(1), one Mg(4), one Cu(2), and one Cu(3) atom. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Mg(3), one Mg(4), and two equivalent Mg(1) atoms. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Mg(2), one Mg(3), one Cu(2), and one Cu(3) atom.
CuOMgO crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted see-saw-like geometry to one O(4), one O(6), and two equivalent O(7) atoms. The Mg(1)-O(4) bond length is 2.06 Å. The Mg(1)-O(6) bond length is 2.03 Å. There is one shorter (2.01 Å) and one longer (2.06 Å) Mg(1)-O(7) bond length. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one O(1), one O(8), and two equivalent O(5) atoms. The Mg(2)-O(1) bond length is 2.03 Å. The Mg(2)-O(8) bond length is 2.08 Å. There is one shorter (2.00 Å) and one longer (2.02 Å) Mg(2)-O(5) bond length. In the third Mg site, Mg(3) is bonded to one O(7), one O(8), and two equivalent O(3) atoms to form MgO4 tetrahedra that share corners with two equivalent Mg(3)O4 tetrahedra and  a cornercorner with one Mg(4)O5 trigonal bipyramid. The Mg(3)-O(7) bond length is 1.93 Å. The Mg(3)-O(8) bond length is 2.02 Å. There is one shorter (1.97 Å) and one longer (1.99 Å) Mg(3)-O(3) bond length. In the fourth Mg site, Mg(4) is bonded to one O(5), one O(6), one O(7), and two equivalent O(2) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Mg(3)O4 tetrahedra,  a cornercorner with one Cu(1)O4 tetrahedra, corners with two equivalent Mg(4)O5 trigonal bipyramids, and  an edgeedge with one Cu(1)O4 tetrahedra. The Mg(4)-O(5) bond length is 2.04 Å. The Mg(4)-O(6) bond length is 2.10 Å. The Mg(4)-O(7) bond length is 2.08 Å. There is one shorter (2.02 Å) and one longer (2.03 Å) Mg(4)-O(2) bond length. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(2), one O(5), and two equivalent O(4) atoms to form distorted CuO4 tetrahedra that share corners with two equivalent Cu(1)O4 tetrahedra,  a cornercorner with one Mg(4)O5 trigonal bipyramid, and  an edgeedge with one Mg(4)O5 trigonal bipyramid. The Cu(1)-O(2) bond length is 1.98 Å. The Cu(1)-O(5) bond length is 2.07 Å. There is one shorter (2.00 Å) and one longer (2.14 Å) Cu(1)-O(4) bond length. In the second Cu site, Cu(2) is bonded in a rectangular see-saw-like geometry to one O(3), one O(4), one O(6), and one O(8) atom. The Cu(2)-O(3) bond length is 1.89 Å. The Cu(2)-O(4) bond length is 1.97 Å. The Cu(2)-O(6) bond length is 1.87 Å. The Cu(2)-O(8) bond length is 2.03 Å. In the third Cu site, Cu(3) is bonded in a rectangular see-saw-like geometry to one O(1), one O(2), one O(6), and one O(8) atom. The Cu(3)-O(1) bond length is 1.92 Å. The Cu(3)-O(2) bond length is 1.92 Å. The Cu(3)-O(6) bond length is 1.87 Å. The Cu(3)-O(8) bond length is 1.98 Å. In the fourth Cu site, Cu(4) is bonded in a trigonal planar geometry to one O(3) and two equivalent O(1) atoms. The Cu(4)-O(3) bond length is 1.89 Å. There is one shorter (1.91 Å) and one longer (1.99 Å) Cu(4)-O(1) bond length. 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 OMgCu3 tetrahedra that share  a cornercorner with one O(2)Mg2Cu2 tetrahedra, corners with two equivalent O(3)Mg2Cu2 tetrahedra, corners with two equivalent O(5)Mg3Cu tetrahedra, and corners with two equivalent O(1)MgCu3 tetrahedra. In the second O site, O(2) is bonded to two equivalent Mg(4), one Cu(1), and one Cu(3) atom to form distorted OMg2Cu2 tetrahedra that share  a cornercorner with one O(5)Mg3Cu tetrahedra,  a cornercorner with one O(1)MgCu3 tetrahedra, corners with two equivalent O(2)Mg2Cu2 tetrahedra, and  an edgeedge with one O(5)Mg3Cu tetrahedra. In the third O site, O(3) is bonded to two equivalent Mg(3), one Cu(2), and one Cu(4) atom to form OMg2Cu2 tetrahedra that share corners with two equivalent O(3)Mg2Cu2 tetrahedra and corners with two equivalent O(1)MgCu3 tetrahedra. In the fourth O site, O(4) is bonded in a distorted see-saw-like geometry to one Mg(1), one Cu(2), and two equivalent Cu(1) atoms. In the fifth O site, O(5) is bonded to one Mg(4), two equivalent Mg(2), and one Cu(1) atom to form distorted OMg3Cu tetrahedra that share  a cornercorner with one O(2)Mg2Cu2 tetrahedra, corners with two equivalent O(5)Mg3Cu tetrahedra, corners with two equivalent O(1)MgCu3 tetrahedra, and  an edgeedge with one O(2)Mg2Cu2 tetrahedra. In the sixth O site, O(6) is bonded in a distorted see-saw-like geometry to one Mg(1), one Mg(4), one Cu(2), and one Cu(3) atom. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Mg(3), one Mg(4), and two equivalent Mg(1) atoms. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Mg(2), one Mg(3), one Cu(2), and one Cu(3) atom.