Ce2Co17 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a 20-coordinate geometry to two equivalent Co(2), six equivalent Co(1), six equivalent Co(3), and six equivalent Co(4) atoms. In the second Ce site, Ce(2) is bonded in a 18-coordinate geometry to six equivalent Co(4) and twelve equivalent Co(1) atoms. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one Ce(1), two equivalent Ce(2), one Co(2), two equivalent Co(1), two equivalent Co(3), and four equivalent Co(4) atoms to form distorted CoCe3Co9 cuboctahedra that share corners with five equivalent Co(3)Ce2Co10 cuboctahedra, corners with eight equivalent Co(4)Ce2Co10 cuboctahedra, corners with ten equivalent Co(1)Ce3Co9 cuboctahedra, edges with two equivalent Co(4)Ce2Co10 cuboctahedra, edges with three equivalent Co(3)Ce2Co10 cuboctahedra, edges with five equivalent Co(1)Ce3Co9 cuboctahedra, faces with two equivalent Co(3)Ce2Co10 cuboctahedra, faces with eight equivalent Co(1)Ce3Co9 cuboctahedra, and faces with ten equivalent Co(4)Ce2Co10 cuboctahedra. In the second Co site, Co(2) is bonded in a 14-coordinate geometry to one Ce(1), one Co(2), three equivalent Co(1), three equivalent Co(3), and six equivalent Co(4) atoms. In the third Co site, Co(3) is bonded to two equivalent Ce(1), two equivalent Co(2), four equivalent Co(1), and four equivalent Co(4) atoms to form CoCe2Co10 cuboctahedra that share corners with four equivalent Co(3)Ce2Co10 cuboctahedra, corners with eight equivalent Co(4)Ce2Co10 cuboctahedra, corners with ten equivalent Co(1)Ce3Co9 cuboctahedra, edges with four equivalent Co(4)Ce2Co10 cuboctahedra, edges with six equivalent Co(1)Ce3Co9 cuboctahedra, faces with four equivalent Co(1)Ce3Co9 cuboctahedra, faces with six equivalent Co(3)Ce2Co10 cuboctahedra, and faces with eight equivalent Co(4)Ce2Co10 cuboctahedra. In the fourth Co site, Co(4) is bonded to one Ce(1), one Ce(2), two equivalent Co(2), two equivalent Co(3), two equivalent Co(4), and four equivalent Co(1) atoms to form distorted CoCe2Co10 cuboctahedra that share corners with four equivalent Co(3)Ce2Co10 cuboctahedra, corners with eight equivalent Co(1)Ce3Co9 cuboctahedra, corners with twelve equivalent Co(4)Ce2Co10 cuboctahedra,  an edgeedge with one Co(4)Ce2Co10 cuboctahedra, edges with two equivalent Co(3)Ce2Co10 cuboctahedra, edges with two equivalent Co(1)Ce3Co9 cuboctahedra, faces with four equivalent Co(3)Ce2Co10 cuboctahedra, faces with seven equivalent Co(4)Ce2Co10 cuboctahedra, and faces with ten equivalent Co(1)Ce3Co9 cuboctahedra.
Ce2Co17 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a 20-coordinate geometry to two equivalent Co(2), six equivalent Co(1), six equivalent Co(3), and six equivalent Co(4) atoms. Both Ce(1)-Co(2) bond lengths are 2.88 Å. All Ce(1)-Co(1) bond lengths are 3.02 Å. All Ce(1)-Co(3) bond lengths are 3.14 Å. All Ce(1)-Co(4) bond lengths are 3.01 Å. In the second Ce site, Ce(2) is bonded in a 18-coordinate geometry to six equivalent Co(4) and twelve equivalent Co(1) atoms. All Ce(2)-Co(4) bond lengths are 2.95 Å. There are six shorter (3.03 Å) and six longer (3.27 Å) Ce(2)-Co(1) bond lengths. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one Ce(1), two equivalent Ce(2), one Co(2), two equivalent Co(1), two equivalent Co(3), and four equivalent Co(4) atoms to form distorted CoCe3Co9 cuboctahedra that share corners with five equivalent Co(3)Ce2Co10 cuboctahedra, corners with eight equivalent Co(4)Ce2Co10 cuboctahedra, corners with ten equivalent Co(1)Ce3Co9 cuboctahedra, edges with two equivalent Co(4)Ce2Co10 cuboctahedra, edges with three equivalent Co(3)Ce2Co10 cuboctahedra, edges with five equivalent Co(1)Ce3Co9 cuboctahedra, faces with two equivalent Co(3)Ce2Co10 cuboctahedra, faces with eight equivalent Co(1)Ce3Co9 cuboctahedra, and faces with ten equivalent Co(4)Ce2Co10 cuboctahedra. The Co(1)-Co(2) bond length is 2.61 Å. Both Co(1)-Co(1) bond lengths are 2.44 Å. Both Co(1)-Co(3) bond lengths are 2.41 Å. There are two shorter (2.52 Å) and two longer (2.55 Å) Co(1)-Co(4) bond lengths. In the second Co site, Co(2) is bonded in a 14-coordinate geometry to one Ce(1), one Co(2), three equivalent Co(1), three equivalent Co(3), and six equivalent Co(4) atoms. The Co(2)-Co(2) bond length is 2.34 Å. All Co(2)-Co(3) bond lengths are 2.55 Å. All Co(2)-Co(4) bond lengths are 2.67 Å. In the third Co site, Co(3) is bonded to two equivalent Ce(1), two equivalent Co(2), four equivalent Co(1), and four equivalent Co(4) atoms to form CoCe2Co10 cuboctahedra that share corners with four equivalent Co(3)Ce2Co10 cuboctahedra, corners with eight equivalent Co(4)Ce2Co10 cuboctahedra, corners with ten equivalent Co(1)Ce3Co9 cuboctahedra, edges with four equivalent Co(4)Ce2Co10 cuboctahedra, edges with six equivalent Co(1)Ce3Co9 cuboctahedra, faces with four equivalent Co(1)Ce3Co9 cuboctahedra, faces with six equivalent Co(3)Ce2Co10 cuboctahedra, and faces with eight equivalent Co(4)Ce2Co10 cuboctahedra. All Co(3)-Co(4) bond lengths are 2.39 Å. In the fourth Co site, Co(4) is bonded to one Ce(1), one Ce(2), two equivalent Co(2), two equivalent Co(3), two equivalent Co(4), and four equivalent Co(1) atoms to form distorted CoCe2Co10 cuboctahedra that share corners with four equivalent Co(3)Ce2Co10 cuboctahedra, corners with eight equivalent Co(1)Ce3Co9 cuboctahedra, corners with twelve equivalent Co(4)Ce2Co10 cuboctahedra,  an edgeedge with one Co(4)Ce2Co10 cuboctahedra, edges with two equivalent Co(3)Ce2Co10 cuboctahedra, edges with two equivalent Co(1)Ce3Co9 cuboctahedra, faces with four equivalent Co(3)Ce2Co10 cuboctahedra, faces with seven equivalent Co(4)Ce2Co10 cuboctahedra, and faces with ten equivalent Co(1)Ce3Co9 cuboctahedra. There is one shorter (2.33 Å) and one longer (2.46 Å) Co(4)-Co(4) bond length.