MgCe5 crystallizes in the hexagonal P-6m2 space group. Mg(1) is bonded to six equivalent Mg(1) and six equivalent Ce(1) atoms to form MgCe6Mg6 cuboctahedra that share corners with six equivalent Mg(1)Ce6Mg6 cuboctahedra, corners with twelve equivalent Ce(2)Ce12 cuboctahedra, edges with six equivalent Mg(1)Ce6Mg6 cuboctahedra, edges with twelve equivalent Ce(1)Ce9Mg3 cuboctahedra, faces with two equivalent Ce(2)Ce12 cuboctahedra, faces with six equivalent Mg(1)Ce6Mg6 cuboctahedra, and faces with twelve equivalent Ce(1)Ce9Mg3 cuboctahedra. There are three inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to three equivalent Mg(1), three equivalent Ce(2), and six equivalent Ce(1) atoms to form CeCe9Mg3 cuboctahedra that share corners with six equivalent Ce(3)Ce12 cuboctahedra, corners with twelve equivalent Ce(1)Ce9Mg3 cuboctahedra, edges with six equivalent Mg(1)Ce6Mg6 cuboctahedra, edges with six equivalent Ce(2)Ce12 cuboctahedra, edges with six equivalent Ce(1)Ce9Mg3 cuboctahedra,  a faceface with one Ce(3)Ce12 cuboctahedra, faces with six equivalent Mg(1)Ce6Mg6 cuboctahedra, faces with six equivalent Ce(2)Ce12 cuboctahedra, and faces with seven equivalent Ce(1)Ce9Mg3 cuboctahedra. In the second Ce site, Ce(2) is bonded to three equivalent Ce(1), three equivalent Ce(3), and six equivalent Ce(2) atoms to form CeCe12 cuboctahedra that share corners with six equivalent Mg(1)Ce6Mg6 cuboctahedra, corners with twelve equivalent Ce(2)Ce12 cuboctahedra, edges with six equivalent Ce(2)Ce12 cuboctahedra, edges with six equivalent Ce(3)Ce12 cuboctahedra, edges with six equivalent Ce(1)Ce9Mg3 cuboctahedra,  a faceface with one Mg(1)Ce6Mg6 cuboctahedra, faces with six equivalent Ce(3)Ce12 cuboctahedra, faces with six equivalent Ce(1)Ce9Mg3 cuboctahedra, and faces with seven equivalent Ce(2)Ce12 cuboctahedra. In the third Ce site, Ce(3) is bonded to six equivalent Ce(2) and six equivalent Ce(3) atoms to form CeCe12 cuboctahedra that share corners with six equivalent Ce(3)Ce12 cuboctahedra, corners with twelve equivalent Ce(1)Ce9Mg3 cuboctahedra, edges with six equivalent Ce(3)Ce12 cuboctahedra, edges with twelve equivalent Ce(2)Ce12 cuboctahedra, faces with two equivalent Ce(1)Ce9Mg3 cuboctahedra, faces with six equivalent Ce(3)Ce12 cuboctahedra, and faces with twelve equivalent Ce(2)Ce12 cuboctahedra.
MgCe5 crystallizes in the hexagonal P-6m2 space group. Mg(1) is bonded to six equivalent Mg(1) and six equivalent Ce(1) atoms to form MgCe6Mg6 cuboctahedra that share corners with six equivalent Mg(1)Ce6Mg6 cuboctahedra, corners with twelve equivalent Ce(2)Ce12 cuboctahedra, edges with six equivalent Mg(1)Ce6Mg6 cuboctahedra, edges with twelve equivalent Ce(1)Ce9Mg3 cuboctahedra, faces with two equivalent Ce(2)Ce12 cuboctahedra, faces with six equivalent Mg(1)Ce6Mg6 cuboctahedra, and faces with twelve equivalent Ce(1)Ce9Mg3 cuboctahedra. All Mg(1)-Mg(1) bond lengths are 3.20 Å. All Mg(1)-Ce(1) bond lengths are 3.48 Å. There are three inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to three equivalent Mg(1), three equivalent Ce(2), and six equivalent Ce(1) atoms to form CeCe9Mg3 cuboctahedra that share corners with six equivalent Ce(3)Ce12 cuboctahedra, corners with twelve equivalent Ce(1)Ce9Mg3 cuboctahedra, edges with six equivalent Mg(1)Ce6Mg6 cuboctahedra, edges with six equivalent Ce(2)Ce12 cuboctahedra, edges with six equivalent Ce(1)Ce9Mg3 cuboctahedra,  a faceface with one Ce(3)Ce12 cuboctahedra, faces with six equivalent Mg(1)Ce6Mg6 cuboctahedra, faces with six equivalent Ce(2)Ce12 cuboctahedra, and faces with seven equivalent Ce(1)Ce9Mg3 cuboctahedra. All Ce(1)-Ce(2) bond lengths are 3.50 Å. All Ce(1)-Ce(1) bond lengths are 3.20 Å. In the second Ce site, Ce(2) is bonded to three equivalent Ce(1), three equivalent Ce(3), and six equivalent Ce(2) atoms to form CeCe12 cuboctahedra that share corners with six equivalent Mg(1)Ce6Mg6 cuboctahedra, corners with twelve equivalent Ce(2)Ce12 cuboctahedra, edges with six equivalent Ce(2)Ce12 cuboctahedra, edges with six equivalent Ce(3)Ce12 cuboctahedra, edges with six equivalent Ce(1)Ce9Mg3 cuboctahedra,  a faceface with one Mg(1)Ce6Mg6 cuboctahedra, faces with six equivalent Ce(3)Ce12 cuboctahedra, faces with six equivalent Ce(1)Ce9Mg3 cuboctahedra, and faces with seven equivalent Ce(2)Ce12 cuboctahedra. All Ce(2)-Ce(3) bond lengths are 3.45 Å. All Ce(2)-Ce(2) bond lengths are 3.20 Å. In the third Ce site, Ce(3) is bonded to six equivalent Ce(2) and six equivalent Ce(3) atoms to form CeCe12 cuboctahedra that share corners with six equivalent Ce(3)Ce12 cuboctahedra, corners with twelve equivalent Ce(1)Ce9Mg3 cuboctahedra, edges with six equivalent Ce(3)Ce12 cuboctahedra, edges with twelve equivalent Ce(2)Ce12 cuboctahedra, faces with two equivalent Ce(1)Ce9Mg3 cuboctahedra, faces with six equivalent Ce(3)Ce12 cuboctahedra, and faces with twelve equivalent Ce(2)Ce12 cuboctahedra. All Ce(3)-Ce(3) bond lengths are 3.20 Å.