Ce2HfCo16 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Ce sites. In the first Ce site, Ce(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 Ce site, Ce(2) is bonded in a 18-coordinate geometry to six equivalent Co(1), six equivalent Co(2), and six equivalent Co(3) atoms. Hf(1) is bonded in a 14-coordinate geometry to one Ce(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(5) is bonded in a 12-coordinate geometry to two equivalent Ce(1), two equivalent Hf(1), four equivalent Co(1), and four equivalent Co(3) atoms. In the second Co site, Co(6) is bonded in a distorted linear geometry to one Ce(1), one Hf(1), three equivalent Co(2), and three equivalent Co(4) atoms. In the third Co site, Co(1) is bonded in a 11-coordinate geometry to one Ce(1), one Ce(2), one Hf(1), one Co(4), one Co(5), two equivalent Co(1), two equivalent Co(2), and two equivalent Co(3) atoms. In the fourth Co site, Co(2) is bonded to one Ce(1), two equivalent Ce(2), one Co(6), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(1) atoms to form distorted CoCe3Co9 cuboctahedra that share corners with two equivalent Co(4)Ce2Co10 cuboctahedra, corners with two equivalent Co(2)Ce3Co9 cuboctahedra, corners with eight equivalent Co(3)Ce3HfCo8 cuboctahedra,  an edgeedge with one Co(4)Ce2Co10 cuboctahedra,  an edgeedge with one Co(2)Ce3Co9 cuboctahedra, edges with four equivalent Co(3)Ce3HfCo8 cuboctahedra, faces with two equivalent Co(4)Ce2Co10 cuboctahedra, faces with two equivalent Co(3)Ce3HfCo8 cuboctahedra, and faces with six equivalent Co(2)Ce3Co9 cuboctahedra. In the fifth Co site, Co(3) is bonded to one Ce(1), two equivalent Ce(2), one Hf(1), two equivalent Co(3), two equivalent Co(5), and four equivalent Co(1) atoms to form distorted CoCe3HfCo8 cuboctahedra that share corners with two equivalent Co(3)Ce3HfCo8 cuboctahedra, corners with three equivalent Co(4)Ce2Co10 cuboctahedra, corners with eight equivalent Co(2)Ce3Co9 cuboctahedra,  an edgeedge with one Co(3)Ce3HfCo8 cuboctahedra, edges with two equivalent Co(4)Ce2Co10 cuboctahedra, edges with four equivalent Co(2)Ce3Co9 cuboctahedra, faces with two equivalent Co(2)Ce3Co9 cuboctahedra, and faces with six equivalent Co(3)Ce3HfCo8 cuboctahedra. In the sixth Co site, Co(4) is bonded to two equivalent Ce(1), two equivalent Co(6), four equivalent Co(1), and four equivalent Co(2) atoms to form CoCe2Co10 cuboctahedra that share corners with four equivalent Co(2)Ce3Co9 cuboctahedra, corners with six equivalent Co(3)Ce3HfCo8 cuboctahedra, edges with two equivalent Co(2)Ce3Co9 cuboctahedra, edges with four equivalent Co(3)Ce3HfCo8 cuboctahedra, faces with four equivalent Co(4)Ce2Co10 cuboctahedra, and faces with four equivalent Co(2)Ce3Co9 cuboctahedra.
Ce2HfCo16 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Ce sites. In the first Ce site, Ce(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 Ce(1)-Hf(1) bond length is 3.17 Å. The Ce(1)-Co(6) bond length is 2.66 Å. All Ce(1)-Co(2) bond lengths are 3.02 Å. All Ce(1)-Co(3) bond lengths are 3.16 Å. All Ce(1)-Co(4) bond lengths are 3.08 Å. All Ce(1)-Co(5) bond lengths are 3.25 Å. All Ce(1)-Co(1) bond lengths are 2.95 Å. In the second Ce site, Ce(2) is bonded in a 18-coordinate geometry to six equivalent Co(1), six equivalent Co(2), and six equivalent Co(3) atoms. All Ce(2)-Co(1) bond lengths are 2.87 Å. There are three shorter (3.11 Å) and three longer (3.24 Å) Ce(2)-Co(2) bond lengths. There are three shorter (3.02 Å) and three longer (3.25 Å) Ce(2)-Co(3) bond lengths. Hf(1) is bonded in a 14-coordinate geometry to one Ce(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 2.41 Å. All Hf(1)-Co(3) bond lengths are 2.70 Å. All Hf(1)-Co(5) bond lengths are 2.60 Å. All Hf(1)-Co(1) bond lengths are 2.75 Å. There are six inequivalent Co sites. In the first Co site, Co(5) is bonded in a 12-coordinate geometry to two equivalent Ce(1), two equivalent Hf(1), four equivalent Co(1), and four equivalent Co(3) atoms. All Co(5)-Co(1) bond lengths are 2.46 Å. All Co(5)-Co(3) bond lengths are 2.43 Å. In the second Co site, Co(6) is bonded in a distorted linear geometry to one Ce(1), one Hf(1), three equivalent Co(2), and three equivalent Co(4) atoms. All Co(6)-Co(2) bond lengths are 2.54 Å. All Co(6)-Co(4) bond lengths are 2.51 Å. In the third Co site, Co(1) is bonded in a 11-coordinate geometry to one Ce(1), one Ce(2), one Hf(1), one Co(4), one Co(5), two equivalent Co(1), two equivalent Co(2), and two equivalent Co(3) atoms. The Co(1)-Co(4) bond length is 2.44 Å. There is one shorter (2.45 Å) and one longer (2.61 Å) Co(1)-Co(1) bond length. There is one shorter (2.48 Å) and one longer (2.55 Å) Co(1)-Co(2) bond length. There is one shorter (2.50 Å) and one longer (2.57 Å) Co(1)-Co(3) bond length. In the fourth Co site, Co(2) is bonded to one Ce(1), two equivalent Ce(2), one Co(6), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(1) atoms to form distorted CoCe3Co9 cuboctahedra that share corners with two equivalent Co(4)Ce2Co10 cuboctahedra, corners with two equivalent Co(2)Ce3Co9 cuboctahedra, corners with eight equivalent Co(3)Ce3HfCo8 cuboctahedra,  an edgeedge with one Co(4)Ce2Co10 cuboctahedra,  an edgeedge with one Co(2)Ce3Co9 cuboctahedra, edges with four equivalent Co(3)Ce3HfCo8 cuboctahedra, faces with two equivalent Co(4)Ce2Co10 cuboctahedra, faces with two equivalent Co(3)Ce3HfCo8 cuboctahedra, and faces with six equivalent Co(2)Ce3Co9 cuboctahedra. Both Co(2)-Co(2) bond lengths are 2.41 Å. Both Co(2)-Co(4) bond lengths are 2.41 Å. In the fifth Co site, Co(3) is bonded to one Ce(1), two equivalent Ce(2), one Hf(1), two equivalent Co(3), two equivalent Co(5), and four equivalent Co(1) atoms to form distorted CoCe3HfCo8 cuboctahedra that share corners with two equivalent Co(3)Ce3HfCo8 cuboctahedra, corners with three equivalent Co(4)Ce2Co10 cuboctahedra, corners with eight equivalent Co(2)Ce3Co9 cuboctahedra,  an edgeedge with one Co(3)Ce3HfCo8 cuboctahedra, edges with two equivalent Co(4)Ce2Co10 cuboctahedra, edges with four equivalent Co(2)Ce3Co9 cuboctahedra, faces with two equivalent Co(2)Ce3Co9 cuboctahedra, and faces with six equivalent Co(3)Ce3HfCo8 cuboctahedra. Both Co(3)-Co(3) bond lengths are 2.39 Å. In the sixth Co site, Co(4) is bonded to two equivalent Ce(1), two equivalent Co(6), four equivalent Co(1), and four equivalent Co(2) atoms to form CoCe2Co10 cuboctahedra that share corners with four equivalent Co(2)Ce3Co9 cuboctahedra, corners with six equivalent Co(3)Ce3HfCo8 cuboctahedra, edges with two equivalent Co(2)Ce3Co9 cuboctahedra, edges with four equivalent Co(3)Ce3HfCo8 cuboctahedra, faces with four equivalent Co(4)Ce2Co10 cuboctahedra, and faces with four equivalent Co(2)Ce3Co9 cuboctahedra.