Sm2HfCo16 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 20-coordinate geometry to one Hf(1), one Co(6), three equivalent Co(2), three equivalent Co(3), three equivalent Co(4), three equivalent Co(5), and six equivalent Co(1) atoms. In the second Sm site, Sm(2) is bonded in a 18-coordinate geometry to six equivalent Co(1), six equivalent Co(4), and six equivalent Co(5) atoms. Hf(1) is bonded in a 14-coordinate geometry to one Sm(1), one Co(6), three equivalent Co(3), three equivalent Co(5), and six equivalent Co(1) atoms. There are six inequivalent Co sites. In the first Co site, Co(6) is bonded in a distorted linear geometry to one Sm(1), one Hf(1), three equivalent Co(2), three equivalent Co(4), and six equivalent Co(1) atoms. In the second Co site, Co(1) is bonded in a 12-coordinate geometry to one Sm(1), one Sm(2), one Hf(1), one Co(2), one Co(3), one Co(6), two equivalent Co(1), two equivalent Co(4), and two equivalent Co(5) atoms. In the third Co site, Co(2) is bonded to two equivalent Sm(1), two equivalent Co(6), four equivalent Co(1), and four equivalent Co(4) atoms to form CoSm2Co10 cuboctahedra that share corners with four equivalent Co(3)Sm2Hf2Co8 cuboctahedra, corners with four equivalent Co(4)Sm3Co9 cuboctahedra, corners with six equivalent Co(5)Sm3HfCo8 cuboctahedra, edges with two equivalent Co(4)Sm3Co9 cuboctahedra, edges with four equivalent Co(5)Sm3HfCo8 cuboctahedra, faces with two equivalent Co(3)Sm2Hf2Co8 cuboctahedra, faces with four equivalent Co(2)Sm2Co10 cuboctahedra, and faces with four equivalent Co(4)Sm3Co9 cuboctahedra. In the fourth Co site, Co(3) is bonded to two equivalent Sm(1), two equivalent Hf(1), four equivalent Co(1), and four equivalent Co(5) atoms to form distorted CoSm2Hf2Co8 cuboctahedra that share corners with four equivalent Co(2)Sm2Co10 cuboctahedra, corners with four equivalent Co(5)Sm3HfCo8 cuboctahedra, corners with six equivalent Co(4)Sm3Co9 cuboctahedra, edges with two equivalent Co(5)Sm3HfCo8 cuboctahedra, edges with four equivalent Co(4)Sm3Co9 cuboctahedra, faces with two equivalent Co(2)Sm2Co10 cuboctahedra, faces with four equivalent Co(3)Sm2Hf2Co8 cuboctahedra, and faces with four equivalent Co(5)Sm3HfCo8 cuboctahedra. In the fifth Co site, Co(4) is bonded to one Sm(1), two equivalent Sm(2), one Co(6), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(1) atoms to form distorted CoSm3Co9 cuboctahedra that share corners with two equivalent Co(2)Sm2Co10 cuboctahedra, corners with two equivalent Co(4)Sm3Co9 cuboctahedra, corners with three equivalent Co(3)Sm2Hf2Co8 cuboctahedra, corners with eight equivalent Co(5)Sm3HfCo8 cuboctahedra,  an edgeedge with one Co(2)Sm2Co10 cuboctahedra,  an edgeedge with one Co(4)Sm3Co9 cuboctahedra, edges with two equivalent Co(3)Sm2Hf2Co8 cuboctahedra, edges with four equivalent Co(5)Sm3HfCo8 cuboctahedra, faces with two equivalent Co(2)Sm2Co10 cuboctahedra, faces with two equivalent Co(5)Sm3HfCo8 cuboctahedra, and faces with six equivalent Co(4)Sm3Co9 cuboctahedra. In the sixth Co site, Co(5) is bonded to one Sm(1), two equivalent Sm(2), one Hf(1), two equivalent Co(3), two equivalent Co(5), and four equivalent Co(1) atoms to form distorted CoSm3HfCo8 cuboctahedra that share corners with two equivalent Co(3)Sm2Hf2Co8 cuboctahedra, corners with two equivalent Co(5)Sm3HfCo8 cuboctahedra, corners with three equivalent Co(2)Sm2Co10 cuboctahedra, corners with eight equivalent Co(4)Sm3Co9 cuboctahedra,  an edgeedge with one Co(3)Sm2Hf2Co8 cuboctahedra,  an edgeedge with one Co(5)Sm3HfCo8 cuboctahedra, edges with two equivalent Co(2)Sm2Co10 cuboctahedra, edges with four equivalent Co(4)Sm3Co9 cuboctahedra, faces with two equivalent Co(3)Sm2Hf2Co8 cuboctahedra, faces with two equivalent Co(4)Sm3Co9 cuboctahedra, and faces with six equivalent Co(5)Sm3HfCo8 cuboctahedra.
Sm2HfCo16 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Sm sites. In the first Sm site, Sm(1) is bonded in a 20-coordinate geometry to one Hf(1), one Co(6), three equivalent Co(2), three equivalent Co(3), three equivalent Co(4), three equivalent Co(5), and six equivalent Co(1) atoms. The Sm(1)-Hf(1) bond length is 3.10 Å. The Sm(1)-Co(6) bond length is 2.71 Å. All Sm(1)-Co(2) bond lengths are 3.10 Å. All Sm(1)-Co(3) bond lengths are 3.26 Å. All Sm(1)-Co(4) bond lengths are 3.03 Å. All Sm(1)-Co(5) bond lengths are 3.19 Å. All Sm(1)-Co(1) bond lengths are 3.00 Å. In the second Sm site, Sm(2) is bonded in a 18-coordinate geometry to six equivalent Co(1), six equivalent Co(4), and six equivalent Co(5) atoms. All Sm(2)-Co(1) bond lengths are 2.95 Å. There are three shorter (3.10 Å) and three longer (3.26 Å) Sm(2)-Co(4) bond lengths. There are three shorter (3.03 Å) and three longer (3.25 Å) Sm(2)-Co(5) bond lengths. Hf(1) is bonded in a 14-coordinate geometry to one Sm(1), one Co(6), three equivalent Co(3), three equivalent Co(5), and six equivalent Co(1) atoms. The Hf(1)-Co(6) bond length is 2.40 Å. All Hf(1)-Co(3) bond lengths are 2.60 Å. All Hf(1)-Co(5) bond lengths are 2.71 Å. All Hf(1)-Co(1) bond lengths are 2.73 Å. There are six inequivalent Co sites. In the first Co site, Co(6) is bonded in a distorted linear geometry to one Sm(1), one Hf(1), three equivalent Co(2), three equivalent Co(4), and six equivalent Co(1) atoms. All Co(6)-Co(2) bond lengths are 2.55 Å. All Co(6)-Co(4) bond lengths are 2.59 Å. All Co(6)-Co(1) bond lengths are 2.79 Å. In the second Co site, Co(1) is bonded in a 12-coordinate geometry to one Sm(1), one Sm(2), one Hf(1), one Co(2), one Co(3), one Co(6), two equivalent Co(1), two equivalent Co(4), and two equivalent Co(5) atoms. The Co(1)-Co(2) bond length is 2.42 Å. The Co(1)-Co(3) bond length is 2.44 Å. There is one shorter (2.43 Å) and one longer (2.53 Å) Co(1)-Co(1) bond length. There is one shorter (2.50 Å) and one longer (2.58 Å) Co(1)-Co(4) bond length. There is one shorter (2.56 Å) and one longer (2.57 Å) Co(1)-Co(5) bond length. In the third Co site, Co(2) is bonded to two equivalent Sm(1), two equivalent Co(6), four equivalent Co(1), and four equivalent Co(4) atoms to form CoSm2Co10 cuboctahedra that share corners with four equivalent Co(3)Sm2Hf2Co8 cuboctahedra, corners with four equivalent Co(4)Sm3Co9 cuboctahedra, corners with six equivalent Co(5)Sm3HfCo8 cuboctahedra, edges with two equivalent Co(4)Sm3Co9 cuboctahedra, edges with four equivalent Co(5)Sm3HfCo8 cuboctahedra, faces with two equivalent Co(3)Sm2Hf2Co8 cuboctahedra, faces with four equivalent Co(2)Sm2Co10 cuboctahedra, and faces with four equivalent Co(4)Sm3Co9 cuboctahedra. All Co(2)-Co(4) bond lengths are 2.43 Å. In the fourth Co site, Co(3) is bonded to two equivalent Sm(1), two equivalent Hf(1), four equivalent Co(1), and four equivalent Co(5) atoms to form distorted CoSm2Hf2Co8 cuboctahedra that share corners with four equivalent Co(2)Sm2Co10 cuboctahedra, corners with four equivalent Co(5)Sm3HfCo8 cuboctahedra, corners with six equivalent Co(4)Sm3Co9 cuboctahedra, edges with two equivalent Co(5)Sm3HfCo8 cuboctahedra, edges with four equivalent Co(4)Sm3Co9 cuboctahedra, faces with two equivalent Co(2)Sm2Co10 cuboctahedra, faces with four equivalent Co(3)Sm2Hf2Co8 cuboctahedra, and faces with four equivalent Co(5)Sm3HfCo8 cuboctahedra. All Co(3)-Co(5) bond lengths are 2.46 Å. In the fifth Co site, Co(4) is bonded to one Sm(1), two equivalent Sm(2), one Co(6), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(1) atoms to form distorted CoSm3Co9 cuboctahedra that share corners with two equivalent Co(2)Sm2Co10 cuboctahedra, corners with two equivalent Co(4)Sm3Co9 cuboctahedra, corners with three equivalent Co(3)Sm2Hf2Co8 cuboctahedra, corners with eight equivalent Co(5)Sm3HfCo8 cuboctahedra,  an edgeedge with one Co(2)Sm2Co10 cuboctahedra,  an edgeedge with one Co(4)Sm3Co9 cuboctahedra, edges with two equivalent Co(3)Sm2Hf2Co8 cuboctahedra, edges with four equivalent Co(5)Sm3HfCo8 cuboctahedra, faces with two equivalent Co(2)Sm2Co10 cuboctahedra, faces with two equivalent Co(5)Sm3HfCo8 cuboctahedra, and faces with six equivalent Co(4)Sm3Co9 cuboctahedra. Both Co(4)-Co(4) bond lengths are 2.44 Å. In the sixth Co site, Co(5) is bonded to one Sm(1), two equivalent Sm(2), one Hf(1), two equivalent Co(3), two equivalent Co(5), and four equivalent Co(1) atoms to form distorted CoSm3HfCo8 cuboctahedra that share corners with two equivalent Co(3)Sm2Hf2Co8 cuboctahedra, corners with two equivalent Co(5)Sm3HfCo8 cuboctahedra, corners with three equivalent Co(2)Sm2Co10 cuboctahedra, corners with eight equivalent Co(4)Sm3Co9 cuboctahedra,  an edgeedge with one Co(3)Sm2Hf2Co8 cuboctahedra,  an edgeedge with one Co(5)Sm3HfCo8 cuboctahedra, edges with two equivalent Co(2)Sm2Co10 cuboctahedra, edges with four equivalent Co(4)Sm3Co9 cuboctahedra, faces with two equivalent Co(3)Sm2Hf2Co8 cuboctahedra, faces with two equivalent Co(4)Sm3Co9 cuboctahedra, and faces with six equivalent Co(5)Sm3HfCo8 cuboctahedra. Both Co(5)-Co(5) bond lengths are 2.39 Å.