MgSm5 crystallizes in the trigonal R32 space group. Mg(1) is bonded to six equivalent Sm(1) and six equivalent Sm(2) atoms to form MgSm12 cuboctahedra that share corners with six equivalent Mg(1)Sm12 cuboctahedra, corners with twelve equivalent Sm(2)Sm9Mg3 cuboctahedra, edges with six equivalent Mg(1)Sm12 cuboctahedra, and faces with eight equivalent Sm(2)Sm9Mg3 cuboctahedra. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 10-coordinate geometry to two equivalent Mg(1), four equivalent Sm(1), and four equivalent Sm(2) atoms. In the second Sm site, Sm(2) is bonded to three equivalent Mg(1), three equivalent Sm(2), and six equivalent Sm(1) atoms to form distorted SmSm9Mg3 cuboctahedra that share corners with six equivalent Mg(1)Sm12 cuboctahedra, corners with twelve equivalent Sm(2)Sm9Mg3 cuboctahedra, edges with six equivalent Sm(2)Sm9Mg3 cuboctahedra, faces with four equivalent Mg(1)Sm12 cuboctahedra, and faces with four equivalent Sm(2)Sm9Mg3 cuboctahedra.
MgSm5 crystallizes in the trigonal R32 space group. Mg(1) is bonded to six equivalent Sm(1) and six equivalent Sm(2) atoms to form MgSm12 cuboctahedra that share corners with six equivalent Mg(1)Sm12 cuboctahedra, corners with twelve equivalent Sm(2)Sm9Mg3 cuboctahedra, edges with six equivalent Mg(1)Sm12 cuboctahedra, and faces with eight equivalent Sm(2)Sm9Mg3 cuboctahedra. All Mg(1)-Sm(1) bond lengths are 3.43 Å. All Mg(1)-Sm(2) bond lengths are 3.62 Å. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 10-coordinate geometry to two equivalent Mg(1), four equivalent Sm(1), and four equivalent Sm(2) atoms. All Sm(1)-Sm(1) bond lengths are 3.41 Å. There are two shorter (3.51 Å) and two longer (3.59 Å) Sm(1)-Sm(2) bond lengths. In the second Sm site, Sm(2) is bonded to three equivalent Mg(1), three equivalent Sm(2), and six equivalent Sm(1) atoms to form distorted SmSm9Mg3 cuboctahedra that share corners with six equivalent Mg(1)Sm12 cuboctahedra, corners with twelve equivalent Sm(2)Sm9Mg3 cuboctahedra, edges with six equivalent Sm(2)Sm9Mg3 cuboctahedra, faces with four equivalent Mg(1)Sm12 cuboctahedra, and faces with four equivalent Sm(2)Sm9Mg3 cuboctahedra. All Sm(2)-Sm(2) bond lengths are 3.64 Å.