Y2Co17 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 20-coordinate geometry to two equivalent Co(3), six equivalent Co(1), six equivalent Co(2), and six equivalent Co(4) atoms. In the second Y site, Y(2) is bonded in a 18-coordinate geometry to six equivalent Co(1) and twelve equivalent Co(4) atoms. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded in a 12-coordinate geometry to one Y(1), one Y(2), two equivalent Co(1), two equivalent Co(2), two equivalent Co(3), and four equivalent Co(4) atoms. In the second Co site, Co(2) is bonded to two equivalent Y(1), two equivalent Co(3), four equivalent Co(1), and four equivalent Co(4) atoms to form CoY2Co10 cuboctahedra that share corners with four equivalent Co(2)Y2Co10 cuboctahedra, corners with ten equivalent Co(4)Y3Co9 cuboctahedra, edges with six equivalent Co(4)Y3Co9 cuboctahedra, faces with four equivalent Co(4)Y3Co9 cuboctahedra, and faces with six equivalent Co(2)Y2Co10 cuboctahedra. In the third Co site, Co(3) is bonded in a 14-coordinate geometry to one Y(1), one Co(3), three equivalent Co(2), three equivalent Co(4), and six equivalent Co(1) atoms. In the fourth Co site, Co(4) is bonded to one Y(1), two equivalent Y(2), one Co(3), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(1) atoms to form distorted CoY3Co9 cuboctahedra that share corners with five equivalent Co(2)Y2Co10 cuboctahedra, corners with ten equivalent Co(4)Y3Co9 cuboctahedra, edges with three equivalent Co(2)Y2Co10 cuboctahedra, edges with five equivalent Co(4)Y3Co9 cuboctahedra, faces with two equivalent Co(2)Y2Co10 cuboctahedra, and faces with eight equivalent Co(4)Y3Co9 cuboctahedra.
Y2Co17 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 20-coordinate geometry to two equivalent Co(3), six equivalent Co(1), six equivalent Co(2), and six equivalent Co(4) atoms. Both Y(1)-Co(3) bond lengths are 2.91 Å. All Y(1)-Co(1) bond lengths are 3.00 Å. All Y(1)-Co(2) bond lengths are 3.15 Å. All Y(1)-Co(4) bond lengths are 3.05 Å. In the second Y site, Y(2) is bonded in a 18-coordinate geometry to six equivalent Co(1) and twelve equivalent Co(4) atoms. All Y(2)-Co(1) bond lengths are 2.95 Å. There are six shorter (3.05 Å) and six longer (3.25 Å) Y(2)-Co(4) bond lengths. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded in a 12-coordinate geometry to one Y(1), one Y(2), two equivalent Co(1), two equivalent Co(2), two equivalent Co(3), and four equivalent Co(4) atoms. There is one shorter (2.36 Å) and one longer (2.46 Å) Co(1)-Co(1) bond length. Both Co(1)-Co(2) bond lengths are 2.40 Å. Both Co(1)-Co(3) bond lengths are 2.67 Å. There are two shorter (2.50 Å) and two longer (2.57 Å) Co(1)-Co(4) bond lengths. In the second Co site, Co(2) is bonded to two equivalent Y(1), two equivalent Co(3), four equivalent Co(1), and four equivalent Co(4) atoms to form CoY2Co10 cuboctahedra that share corners with four equivalent Co(2)Y2Co10 cuboctahedra, corners with ten equivalent Co(4)Y3Co9 cuboctahedra, edges with six equivalent Co(4)Y3Co9 cuboctahedra, faces with four equivalent Co(4)Y3Co9 cuboctahedra, and faces with six equivalent Co(2)Y2Co10 cuboctahedra. Both Co(2)-Co(3) bond lengths are 2.56 Å. All Co(2)-Co(4) bond lengths are 2.41 Å. In the third Co site, Co(3) is bonded in a 14-coordinate geometry to one Y(1), one Co(3), three equivalent Co(2), three equivalent Co(4), and six equivalent Co(1) atoms. The Co(3)-Co(3) bond length is 2.32 Å. All Co(3)-Co(4) bond lengths are 2.61 Å. In the fourth Co site, Co(4) is bonded to one Y(1), two equivalent Y(2), one Co(3), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(1) atoms to form distorted CoY3Co9 cuboctahedra that share corners with five equivalent Co(2)Y2Co10 cuboctahedra, corners with ten equivalent Co(4)Y3Co9 cuboctahedra, edges with three equivalent Co(2)Y2Co10 cuboctahedra, edges with five equivalent Co(4)Y3Co9 cuboctahedra, faces with two equivalent Co(2)Y2Co10 cuboctahedra, and faces with eight equivalent Co(4)Y3Co9 cuboctahedra. Both Co(4)-Co(4) bond lengths are 2.42 Å.