Mg5Ce crystallizes in the trigonal R32 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Mg(2), six equivalent Mg(1), and two equivalent Ce(1) atoms to form MgCe2Mg10 cuboctahedra that share corners with eighteen equivalent Mg(1)Ce2Mg10 cuboctahedra, edges with four equivalent Ce(1)Mg12 cuboctahedra, edges with six equivalent Mg(1)Ce2Mg10 cuboctahedra, edges with eight equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with four equivalent Ce(1)Mg12 cuboctahedra, faces with eight equivalent Mg(1)Ce2Mg10 cuboctahedra, and faces with eight equivalent Mg(2)Ce3Mg9 cuboctahedra. In the second Mg site, Mg(2) is bonded to three equivalent Mg(2), six equivalent Mg(1), and three equivalent Ce(1) atoms to form MgCe3Mg9 cuboctahedra that share corners with six equivalent Ce(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with six equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with twelve equivalent Mg(1)Ce2Mg10 cuboctahedra, faces with four equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with four equivalent Ce(1)Mg12 cuboctahedra, and faces with twelve equivalent Mg(1)Ce2Mg10 cuboctahedra. Ce(1) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form CeMg12 cuboctahedra that share corners with six equivalent Ce(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with six equivalent Ce(1)Mg12 cuboctahedra, edges with twelve equivalent Mg(1)Ce2Mg10 cuboctahedra, faces with eight equivalent Mg(2)Ce3Mg9 cuboctahedra, and faces with twelve equivalent Mg(1)Ce2Mg10 cuboctahedra.
Mg5Ce crystallizes in the trigonal R32 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Mg(2), six equivalent Mg(1), and two equivalent Ce(1) atoms to form MgCe2Mg10 cuboctahedra that share corners with eighteen equivalent Mg(1)Ce2Mg10 cuboctahedra, edges with four equivalent Ce(1)Mg12 cuboctahedra, edges with six equivalent Mg(1)Ce2Mg10 cuboctahedra, edges with eight equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with four equivalent Ce(1)Mg12 cuboctahedra, faces with eight equivalent Mg(1)Ce2Mg10 cuboctahedra, and faces with eight equivalent Mg(2)Ce3Mg9 cuboctahedra. There are two shorter (3.31 Å) and two longer (3.32 Å) Mg(1)-Mg(2) bond lengths. There are two shorter (3.23 Å) and four longer (3.25 Å) Mg(1)-Mg(1) bond lengths. Both Mg(1)-Ce(1) bond lengths are 3.32 Å. In the second Mg site, Mg(2) is bonded to three equivalent Mg(2), six equivalent Mg(1), and three equivalent Ce(1) atoms to form MgCe3Mg9 cuboctahedra that share corners with six equivalent Ce(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with six equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with twelve equivalent Mg(1)Ce2Mg10 cuboctahedra, faces with four equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with four equivalent Ce(1)Mg12 cuboctahedra, and faces with twelve equivalent Mg(1)Ce2Mg10 cuboctahedra. All Mg(2)-Mg(2) bond lengths are 3.24 Å. All Mg(2)-Ce(1) bond lengths are 3.24 Å. Ce(1) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form CeMg12 cuboctahedra that share corners with six equivalent Ce(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with six equivalent Ce(1)Mg12 cuboctahedra, edges with twelve equivalent Mg(1)Ce2Mg10 cuboctahedra, faces with eight equivalent Mg(2)Ce3Mg9 cuboctahedra, and faces with twelve equivalent Mg(1)Ce2Mg10 cuboctahedra.