Sm2Co17 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 18-coordinate geometry to six equivalent Co(3) and twelve equivalent Co(4) atoms. In the second Sm site, Sm(2) is bonded in a 20-coordinate geometry to two equivalent Co(1), six equivalent Co(2), six equivalent Co(3), and six equivalent Co(4) atoms. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded in a 14-coordinate geometry to one Sm(2), one Co(1), three equivalent Co(2), three equivalent Co(4), and six equivalent Co(3) atoms. In the second Co site, Co(2) is bonded to two equivalent Sm(2), two equivalent Co(1), four equivalent Co(3), and four equivalent Co(4) atoms to form CoSm2Co10 cuboctahedra that share corners with four equivalent Co(2)Sm2Co10 cuboctahedra, corners with eight equivalent Co(3)Sm2Co10 cuboctahedra, corners with ten equivalent Co(4)Sm3Co9 cuboctahedra, edges with four equivalent Co(3)Sm2Co10 cuboctahedra, edges with six equivalent Co(4)Sm3Co9 cuboctahedra, faces with four equivalent Co(4)Sm3Co9 cuboctahedra, faces with six equivalent Co(2)Sm2Co10 cuboctahedra, and faces with eight equivalent Co(3)Sm2Co10 cuboctahedra. In the third Co site, Co(3) is bonded to one Sm(1), one Sm(2), two equivalent Co(1), two equivalent Co(2), two equivalent Co(3), and four equivalent Co(4) atoms to form distorted CoSm2Co10 cuboctahedra that share corners with four equivalent Co(2)Sm2Co10 cuboctahedra, corners with eight equivalent Co(4)Sm3Co9 cuboctahedra, corners with twelve equivalent Co(3)Sm2Co10 cuboctahedra,  an edgeedge with one Co(3)Sm2Co10 cuboctahedra, edges with two equivalent Co(2)Sm2Co10 cuboctahedra, edges with two equivalent Co(4)Sm3Co9 cuboctahedra, faces with four equivalent Co(2)Sm2Co10 cuboctahedra, faces with seven equivalent Co(3)Sm2Co10 cuboctahedra, and faces with ten equivalent Co(4)Sm3Co9 cuboctahedra. In the fourth Co site, Co(4) is bonded to one Sm(2), two equivalent Sm(1), one Co(1), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(3) atoms to form distorted CoSm3Co9 cuboctahedra that share corners with five equivalent Co(2)Sm2Co10 cuboctahedra, corners with eight equivalent Co(3)Sm2Co10 cuboctahedra, corners with ten equivalent Co(4)Sm3Co9 cuboctahedra, edges with two equivalent Co(3)Sm2Co10 cuboctahedra, edges with three equivalent Co(2)Sm2Co10 cuboctahedra, edges with five equivalent Co(4)Sm3Co9 cuboctahedra, faces with two equivalent Co(2)Sm2Co10 cuboctahedra, faces with eight equivalent Co(4)Sm3Co9 cuboctahedra, and faces with ten equivalent Co(3)Sm2Co10 cuboctahedra.
Sm2Co17 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 18-coordinate geometry to six equivalent Co(3) and twelve equivalent Co(4) atoms. All Sm(1)-Co(3) bond lengths are 2.94 Å. There are six shorter (3.02 Å) and six longer (3.19 Å) Sm(1)-Co(4) bond lengths. In the second Sm site, Sm(2) is bonded in a 20-coordinate geometry to two equivalent Co(1), six equivalent Co(2), six equivalent Co(3), and six equivalent Co(4) atoms. Both Sm(2)-Co(1) bond lengths are 2.87 Å. All Sm(2)-Co(2) bond lengths are 3.11 Å. All Sm(2)-Co(3) bond lengths are 2.98 Å. All Sm(2)-Co(4) bond lengths are 3.03 Å. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded in a 14-coordinate geometry to one Sm(2), one Co(1), three equivalent Co(2), three equivalent Co(4), and six equivalent Co(3) atoms. The Co(1)-Co(1) bond length is 2.25 Å. All Co(1)-Co(2) bond lengths are 2.54 Å. All Co(1)-Co(4) bond lengths are 2.59 Å. All Co(1)-Co(3) bond lengths are 2.63 Å. In the second Co site, Co(2) is bonded to two equivalent Sm(2), two equivalent Co(1), four equivalent Co(3), and four equivalent Co(4) atoms to form CoSm2Co10 cuboctahedra that share corners with four equivalent Co(2)Sm2Co10 cuboctahedra, corners with eight equivalent Co(3)Sm2Co10 cuboctahedra, corners with ten equivalent Co(4)Sm3Co9 cuboctahedra, edges with four equivalent Co(3)Sm2Co10 cuboctahedra, edges with six equivalent Co(4)Sm3Co9 cuboctahedra, faces with four equivalent Co(4)Sm3Co9 cuboctahedra, faces with six equivalent Co(2)Sm2Co10 cuboctahedra, and faces with eight equivalent Co(3)Sm2Co10 cuboctahedra. All Co(2)-Co(3) bond lengths are 2.36 Å. All Co(2)-Co(4) bond lengths are 2.39 Å. In the third Co site, Co(3) is bonded to one Sm(1), one Sm(2), two equivalent Co(1), two equivalent Co(2), two equivalent Co(3), and four equivalent Co(4) atoms to form distorted CoSm2Co10 cuboctahedra that share corners with four equivalent Co(2)Sm2Co10 cuboctahedra, corners with eight equivalent Co(4)Sm3Co9 cuboctahedra, corners with twelve equivalent Co(3)Sm2Co10 cuboctahedra,  an edgeedge with one Co(3)Sm2Co10 cuboctahedra, edges with two equivalent Co(2)Sm2Co10 cuboctahedra, edges with two equivalent Co(4)Sm3Co9 cuboctahedra, faces with four equivalent Co(2)Sm2Co10 cuboctahedra, faces with seven equivalent Co(3)Sm2Co10 cuboctahedra, and faces with ten equivalent Co(4)Sm3Co9 cuboctahedra. There is one shorter (2.33 Å) and one longer (2.41 Å) Co(3)-Co(3) bond length. There are two shorter (2.45 Å) and two longer (2.56 Å) Co(3)-Co(4) bond lengths. In the fourth Co site, Co(4) is bonded to one Sm(2), two equivalent Sm(1), one Co(1), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(3) atoms to form distorted CoSm3Co9 cuboctahedra that share corners with five equivalent Co(2)Sm2Co10 cuboctahedra, corners with eight equivalent Co(3)Sm2Co10 cuboctahedra, corners with ten equivalent Co(4)Sm3Co9 cuboctahedra, edges with two equivalent Co(3)Sm2Co10 cuboctahedra, edges with three equivalent Co(2)Sm2Co10 cuboctahedra, edges with five equivalent Co(4)Sm3Co9 cuboctahedra, faces with two equivalent Co(2)Sm2Co10 cuboctahedra, faces with eight equivalent Co(4)Sm3Co9 cuboctahedra, and faces with ten equivalent Co(3)Sm2Co10 cuboctahedra. Both Co(4)-Co(4) bond lengths are 2.39 Å.