CuOMgO crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(4), one O(8), two equivalent O(6), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent Mg(4)O6 octahedra,  a cornercorner with one Cu(3)O5 square pyramid,  an edgeedge with one Mg(4)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with two equivalent Cu(2)O5 square pyramids. The corner-sharing octahedral tilt angles are 8°. In the second Mg site, Mg(2) is bonded to one O(1), one O(6), two equivalent O(5), and two equivalent O(8) atoms to form MgO6 octahedra that share corners with two equivalent Mg(3)O6 octahedra,  a cornercorner with one Cu(2)O5 square pyramid,  an edgeedge with one Mg(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra, and edges with two equivalent Cu(3)O5 square pyramids. The corner-sharing octahedral tilt angles are 8°. In the third Mg site, Mg(3) is bonded to one O(2), one O(7), two equivalent O(3), and two equivalent O(8) atoms to form MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with two equivalent Cu(2)O5 square pyramids,  an edgeedge with one Mg(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra,  an edgeedge with one Cu(2)O5 square pyramid, and edges with two equivalent Cu(3)O5 square pyramids. The corner-sharing octahedral tilt angles are 8°. In the fourth Mg site, Mg(4) is bonded to one O(3), one O(5), two equivalent O(2), and two equivalent O(6) atoms to form MgO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Cu(3)O5 square pyramids,  an edgeedge with one Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra,  an edgeedge with one Cu(3)O5 square pyramid, and edges with two equivalent Cu(2)O5 square pyramids. The corner-sharing octahedral tilt angles are 8°. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a rectangular see-saw-like geometry to two equivalent O(4) and two equivalent O(5) atoms. In the second Cu site, Cu(2) is bonded to one O(6), two equivalent O(3), and two equivalent O(4) atoms to form CuO5 square pyramids that share  a cornercorner with one Mg(2)O6 octahedra, corners with two equivalent Mg(3)O6 octahedra,  an edgeedge with one Mg(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra, and edges with two equivalent Cu(2)O5 square pyramids. The corner-sharing octahedral tilt angles range from 1-10°. In the third Cu site, Cu(3) is bonded to one O(8), two equivalent O(1), and two equivalent O(2) atoms to form CuO5 square pyramids that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(4)O6 octahedra,  an edgeedge with one Mg(4)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with two equivalent Cu(3)O5 square pyramids. The corner-sharing octahedral tilt angles range from 1-11°. In the fourth Cu site, Cu(4) is bonded in a rectangular see-saw-like geometry to two equivalent O(1) and two equivalent O(7) atoms. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), two equivalent Cu(3), and two equivalent Cu(4) atoms to form OMgCu4 square pyramids that share  a cornercorner with one O(6)Mg5Cu octahedra, corners with two equivalent O(2)Mg3Cu2 square pyramids, corners with two equivalent O(5)Mg3Cu2 square pyramids, corners with two equivalent O(7)Mg3Cu2 square pyramids, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(2)Mg3Cu2 square pyramid,  an edgeedge with one O(7)Mg3Cu2 square pyramid, and edges with two equivalent O(1)MgCu4 square pyramids. The corner-sharing octahedral tilt angles are 1°. In the second O site, O(2) is bonded to one Mg(3), two equivalent Mg(4), and two equivalent Cu(3) atoms to form OMg3Cu2 square pyramids that share corners with two equivalent O(6)Mg5Cu octahedra,  a cornercorner with one O(7)Mg3Cu2 square pyramid, corners with two equivalent O(5)Mg3Cu2 square pyramids, corners with two equivalent O(1)MgCu4 square pyramids,  an edgeedge with one O(6)Mg5Cu octahedra, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(1)MgCu4 square pyramid, edges with two equivalent O(2)Mg3Cu2 square pyramids, and edges with two equivalent O(3)Mg3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 3°. In the third O site, O(3) is bonded to one Mg(4), two equivalent Mg(3), and two equivalent Cu(2) atoms to form OMg3Cu2 square pyramids that share corners with two equivalent O(8)Mg5Cu octahedra,  a cornercorner with one O(5)Mg3Cu2 square pyramid, corners with two equivalent O(7)Mg3Cu2 square pyramids, corners with two equivalent O(4)MgCu4 square pyramids,  an edgeedge with one O(8)Mg5Cu octahedra, edges with two equivalent O(6)Mg5Cu octahedra,  an edgeedge with one O(4)MgCu4 square pyramid, edges with two equivalent O(2)Mg3Cu2 square pyramids, and edges with two equivalent O(3)Mg3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 3°. In the fourth O site, O(4) is bonded to one Mg(1), two equivalent Cu(1), and two equivalent Cu(2) atoms to form OMgCu4 square pyramids that share  a cornercorner with one O(8)Mg5Cu octahedra, corners with two equivalent O(3)Mg3Cu2 square pyramids, corners with two equivalent O(5)Mg3Cu2 square pyramids, corners with two equivalent O(7)Mg3Cu2 square pyramids, edges with two equivalent O(6)Mg5Cu octahedra,  an edgeedge with one O(3)Mg3Cu2 square pyramid,  an edgeedge with one O(5)Mg3Cu2 square pyramid, and edges with two equivalent O(4)MgCu4 square pyramids. The corner-sharing octahedral tilt angles are 1°. In the fifth O site, O(5) is bonded to one Mg(4), two equivalent Mg(2), and two equivalent Cu(1) atoms to form OMg3Cu2 square pyramids that share corners with two equivalent O(8)Mg5Cu octahedra,  a cornercorner with one O(3)Mg3Cu2 square pyramid, corners with two equivalent O(2)Mg3Cu2 square pyramids, corners with two equivalent O(1)MgCu4 square pyramids, corners with two equivalent O(4)MgCu4 square pyramids,  an edgeedge with one O(8)Mg5Cu octahedra, edges with two equivalent O(6)Mg5Cu octahedra,  an edgeedge with one O(4)MgCu4 square pyramid, and edges with two equivalent O(5)Mg3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 7°. In the sixth O site, O(6) is bonded to one Mg(2), two equivalent Mg(1), two equivalent Mg(4), and one Cu(2) atom to form OMg5Cu octahedra that share  a cornercorner with one O(1)MgCu4 square pyramid, corners with two equivalent O(2)Mg3Cu2 square pyramids, corners with two equivalent O(7)Mg3Cu2 square pyramids, edges with two equivalent O(6)Mg5Cu octahedra, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(2)Mg3Cu2 square pyramid,  an edgeedge with one O(7)Mg3Cu2 square pyramid, edges with two equivalent O(3)Mg3Cu2 square pyramids, edges with two equivalent O(5)Mg3Cu2 square pyramids, and edges with two equivalent O(4)MgCu4 square pyramids. In the seventh O site, O(7) is bonded to one Mg(3), two equivalent Mg(1), and two equivalent Cu(4) atoms to form OMg3Cu2 square pyramids that share corners with two equivalent O(6)Mg5Cu octahedra,  a cornercorner with one O(2)Mg3Cu2 square pyramid, corners with two equivalent O(3)Mg3Cu2 square pyramids, corners with two equivalent O(1)MgCu4 square pyramids, corners with two equivalent O(4)MgCu4 square pyramids,  an edgeedge with one O(6)Mg5Cu octahedra, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(1)MgCu4 square pyramid, and edges with two equivalent O(7)Mg3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 7°. In the eighth O site, O(8) is bonded to one Mg(1), two equivalent Mg(2), two equivalent Mg(3), and one Cu(3) atom to form OMg5Cu octahedra that share  a cornercorner with one O(4)MgCu4 square pyramid, corners with two equivalent O(3)Mg3Cu2 square pyramids, corners with two equivalent O(5)Mg3Cu2 square pyramids, edges with two equivalent O(6)Mg5Cu octahedra, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(3)Mg3Cu2 square pyramid,  an edgeedge with one O(5)Mg3Cu2 square pyramid, edges with two equivalent O(2)Mg3Cu2 square pyramids, edges with two equivalent O(7)Mg3Cu2 square pyramids, and edges with two equivalent O(1)MgCu4 square pyramids.
CuOMgO crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(4), one O(8), two equivalent O(6), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent Mg(4)O6 octahedra,  a cornercorner with one Cu(3)O5 square pyramid,  an edgeedge with one Mg(4)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with two equivalent Cu(2)O5 square pyramids. The corner-sharing octahedral tilt angles are 8°. The Mg(1)-O(4) bond length is 2.23 Å. The Mg(1)-O(8) bond length is 2.14 Å. There is one shorter (2.04 Å) and one longer (2.05 Å) Mg(1)-O(6) bond length. Both Mg(1)-O(7) bond lengths are 2.13 Å. In the second Mg site, Mg(2) is bonded to one O(1), one O(6), two equivalent O(5), and two equivalent O(8) atoms to form MgO6 octahedra that share corners with two equivalent Mg(3)O6 octahedra,  a cornercorner with one Cu(2)O5 square pyramid,  an edgeedge with one Mg(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra, and edges with two equivalent Cu(3)O5 square pyramids. The corner-sharing octahedral tilt angles are 8°. The Mg(2)-O(1) bond length is 2.26 Å. The Mg(2)-O(6) bond length is 2.15 Å. There is one shorter (2.12 Å) and one longer (2.13 Å) Mg(2)-O(5) bond length. There is one shorter (2.03 Å) and one longer (2.04 Å) Mg(2)-O(8) bond length. In the third Mg site, Mg(3) is bonded to one O(2), one O(7), two equivalent O(3), and two equivalent O(8) atoms to form MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with two equivalent Cu(2)O5 square pyramids,  an edgeedge with one Mg(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra,  an edgeedge with one Cu(2)O5 square pyramid, and edges with two equivalent Cu(3)O5 square pyramids. The corner-sharing octahedral tilt angles are 8°. The Mg(3)-O(2) bond length is 2.20 Å. The Mg(3)-O(7) bond length is 2.17 Å. Both Mg(3)-O(3) bond lengths are 2.10 Å. There is one shorter (2.04 Å) and one longer (2.05 Å) Mg(3)-O(8) bond length. In the fourth Mg site, Mg(4) is bonded to one O(3), one O(5), two equivalent O(2), and two equivalent O(6) atoms to form MgO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Cu(3)O5 square pyramids,  an edgeedge with one Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra,  an edgeedge with one Cu(3)O5 square pyramid, and edges with two equivalent Cu(2)O5 square pyramids. The corner-sharing octahedral tilt angles are 8°. The Mg(4)-O(3) bond length is 2.22 Å. The Mg(4)-O(5) bond length is 2.18 Å. Both Mg(4)-O(2) bond lengths are 2.10 Å. There is one shorter (2.04 Å) and one longer (2.05 Å) Mg(4)-O(6) bond length. There are four inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a rectangular see-saw-like geometry to two equivalent O(4) and two equivalent O(5) atoms. There is one shorter (1.99 Å) and one longer (2.01 Å) Cu(1)-O(4) bond length. There is one shorter (1.95 Å) and one longer (1.97 Å) Cu(1)-O(5) bond length. In the second Cu site, Cu(2) is bonded to one O(6), two equivalent O(3), and two equivalent O(4) atoms to form CuO5 square pyramids that share  a cornercorner with one Mg(2)O6 octahedra, corners with two equivalent Mg(3)O6 octahedra,  an edgeedge with one Mg(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(4)O6 octahedra, and edges with two equivalent Cu(2)O5 square pyramids. The corner-sharing octahedral tilt angles range from 1-10°. The Cu(2)-O(6) bond length is 2.46 Å. There is one shorter (1.96 Å) and one longer (1.97 Å) Cu(2)-O(3) bond length. There is one shorter (2.02 Å) and one longer (2.03 Å) Cu(2)-O(4) bond length. In the third Cu site, Cu(3) is bonded to one O(8), two equivalent O(1), and two equivalent O(2) atoms to form CuO5 square pyramids that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(4)O6 octahedra,  an edgeedge with one Mg(4)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, and edges with two equivalent Cu(3)O5 square pyramids. The corner-sharing octahedral tilt angles range from 1-11°. The Cu(3)-O(8) bond length is 2.46 Å. There is one shorter (2.01 Å) and one longer (2.03 Å) Cu(3)-O(1) bond length. Both Cu(3)-O(2) bond lengths are 1.96 Å. In the fourth Cu site, Cu(4) is bonded in a rectangular see-saw-like geometry to two equivalent O(1) and two equivalent O(7) atoms. There is one shorter (1.99 Å) and one longer (2.02 Å) Cu(4)-O(1) bond length. There is one shorter (1.95 Å) and one longer (1.97 Å) Cu(4)-O(7) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), two equivalent Cu(3), and two equivalent Cu(4) atoms to form OMgCu4 square pyramids that share  a cornercorner with one O(6)Mg5Cu octahedra, corners with two equivalent O(2)Mg3Cu2 square pyramids, corners with two equivalent O(5)Mg3Cu2 square pyramids, corners with two equivalent O(7)Mg3Cu2 square pyramids, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(2)Mg3Cu2 square pyramid,  an edgeedge with one O(7)Mg3Cu2 square pyramid, and edges with two equivalent O(1)MgCu4 square pyramids. The corner-sharing octahedral tilt angles are 1°. In the second O site, O(2) is bonded to one Mg(3), two equivalent Mg(4), and two equivalent Cu(3) atoms to form OMg3Cu2 square pyramids that share corners with two equivalent O(6)Mg5Cu octahedra,  a cornercorner with one O(7)Mg3Cu2 square pyramid, corners with two equivalent O(5)Mg3Cu2 square pyramids, corners with two equivalent O(1)MgCu4 square pyramids,  an edgeedge with one O(6)Mg5Cu octahedra, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(1)MgCu4 square pyramid, edges with two equivalent O(2)Mg3Cu2 square pyramids, and edges with two equivalent O(3)Mg3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 3°. In the third O site, O(3) is bonded to one Mg(4), two equivalent Mg(3), and two equivalent Cu(2) atoms to form OMg3Cu2 square pyramids that share corners with two equivalent O(8)Mg5Cu octahedra,  a cornercorner with one O(5)Mg3Cu2 square pyramid, corners with two equivalent O(7)Mg3Cu2 square pyramids, corners with two equivalent O(4)MgCu4 square pyramids,  an edgeedge with one O(8)Mg5Cu octahedra, edges with two equivalent O(6)Mg5Cu octahedra,  an edgeedge with one O(4)MgCu4 square pyramid, edges with two equivalent O(2)Mg3Cu2 square pyramids, and edges with two equivalent O(3)Mg3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 3°. In the fourth O site, O(4) is bonded to one Mg(1), two equivalent Cu(1), and two equivalent Cu(2) atoms to form OMgCu4 square pyramids that share  a cornercorner with one O(8)Mg5Cu octahedra, corners with two equivalent O(3)Mg3Cu2 square pyramids, corners with two equivalent O(5)Mg3Cu2 square pyramids, corners with two equivalent O(7)Mg3Cu2 square pyramids, edges with two equivalent O(6)Mg5Cu octahedra,  an edgeedge with one O(3)Mg3Cu2 square pyramid,  an edgeedge with one O(5)Mg3Cu2 square pyramid, and edges with two equivalent O(4)MgCu4 square pyramids. The corner-sharing octahedral tilt angles are 1°. In the fifth O site, O(5) is bonded to one Mg(4), two equivalent Mg(2), and two equivalent Cu(1) atoms to form OMg3Cu2 square pyramids that share corners with two equivalent O(8)Mg5Cu octahedra,  a cornercorner with one O(3)Mg3Cu2 square pyramid, corners with two equivalent O(2)Mg3Cu2 square pyramids, corners with two equivalent O(1)MgCu4 square pyramids, corners with two equivalent O(4)MgCu4 square pyramids,  an edgeedge with one O(8)Mg5Cu octahedra, edges with two equivalent O(6)Mg5Cu octahedra,  an edgeedge with one O(4)MgCu4 square pyramid, and edges with two equivalent O(5)Mg3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 7°. In the sixth O site, O(6) is bonded to one Mg(2), two equivalent Mg(1), two equivalent Mg(4), and one Cu(2) atom to form OMg5Cu octahedra that share  a cornercorner with one O(1)MgCu4 square pyramid, corners with two equivalent O(2)Mg3Cu2 square pyramids, corners with two equivalent O(7)Mg3Cu2 square pyramids, edges with two equivalent O(6)Mg5Cu octahedra, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(2)Mg3Cu2 square pyramid,  an edgeedge with one O(7)Mg3Cu2 square pyramid, edges with two equivalent O(3)Mg3Cu2 square pyramids, edges with two equivalent O(5)Mg3Cu2 square pyramids, and edges with two equivalent O(4)MgCu4 square pyramids. In the seventh O site, O(7) is bonded to one Mg(3), two equivalent Mg(1), and two equivalent Cu(4) atoms to form OMg3Cu2 square pyramids that share corners with two equivalent O(6)Mg5Cu octahedra,  a cornercorner with one O(2)Mg3Cu2 square pyramid, corners with two equivalent O(3)Mg3Cu2 square pyramids, corners with two equivalent O(1)MgCu4 square pyramids, corners with two equivalent O(4)MgCu4 square pyramids,  an edgeedge with one O(6)Mg5Cu octahedra, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(1)MgCu4 square pyramid, and edges with two equivalent O(7)Mg3Cu2 square pyramids. The corner-sharing octahedral tilt angles are 7°. In the eighth O site, O(8) is bonded to one Mg(1), two equivalent Mg(2), two equivalent Mg(3), and one Cu(3) atom to form OMg5Cu octahedra that share  a cornercorner with one O(4)MgCu4 square pyramid, corners with two equivalent O(3)Mg3Cu2 square pyramids, corners with two equivalent O(5)Mg3Cu2 square pyramids, edges with two equivalent O(6)Mg5Cu octahedra, edges with two equivalent O(8)Mg5Cu octahedra,  an edgeedge with one O(3)Mg3Cu2 square pyramid,  an edgeedge with one O(5)Mg3Cu2 square pyramid, edges with two equivalent O(2)Mg3Cu2 square pyramids, edges with two equivalent O(7)Mg3Cu2 square pyramids, and edges with two equivalent O(1)MgCu4 square pyramids.