SmYCo17 crystallizes in the trigonal R3m space group. Sm(1) is bonded in a 19-coordinate geometry to one Co(6), three equivalent Co(2), three equivalent Co(4), six equivalent Co(1), and six equivalent Co(3) atoms. Y(1) is bonded in a 19-coordinate geometry to one Co(5), three equivalent Co(1), three equivalent Co(4), six equivalent Co(2), and six equivalent Co(3) atoms. There are six inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent Sm(1), one Y(1), one Co(6), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(3) atoms to form CoSm2YCo9 cuboctahedra that share corners with two equivalent Co(1)Sm2YCo9 cuboctahedra, corners with five equivalent Co(4)SmYCo10 cuboctahedra, corners with eight equivalent Co(2)SmY2Co9 cuboctahedra, corners with eight equivalent Co(3)SmYCo10 cuboctahedra,  an edgeedge with one Co(2)SmY2Co9 cuboctahedra, edges with two equivalent Co(3)SmYCo10 cuboctahedra, edges with three equivalent Co(4)SmYCo10 cuboctahedra, edges with four equivalent Co(1)Sm2YCo9 cuboctahedra, faces with three equivalent Co(2)SmY2Co9 cuboctahedra, faces with three equivalent Co(4)SmYCo10 cuboctahedra, faces with four equivalent Co(1)Sm2YCo9 cuboctahedra, and faces with ten equivalent Co(3)SmYCo10 cuboctahedra. In the second Co site, Co(2) is bonded to one Sm(1), two equivalent Y(1), one Co(5), two equivalent Co(1), two equivalent Co(4), and four equivalent Co(3) atoms to form CoSmY2Co9 cuboctahedra that share corners with two equivalent Co(2)SmY2Co9 cuboctahedra, corners with five equivalent Co(4)SmYCo10 cuboctahedra, corners with eight equivalent Co(1)Sm2YCo9 cuboctahedra, corners with eight equivalent Co(3)SmYCo10 cuboctahedra,  an edgeedge with one Co(1)Sm2YCo9 cuboctahedra, edges with two equivalent Co(3)SmYCo10 cuboctahedra, edges with three equivalent Co(4)SmYCo10 cuboctahedra, edges with four equivalent Co(2)SmY2Co9 cuboctahedra, faces with three equivalent Co(1)Sm2YCo9 cuboctahedra, faces with three equivalent Co(4)SmYCo10 cuboctahedra, faces with four equivalent Co(2)SmY2Co9 cuboctahedra, and faces with ten equivalent Co(3)SmYCo10 cuboctahedra. In the third Co site, Co(3) is bonded to one Sm(1), one Y(1), one Co(5), one Co(6), two equivalent Co(1), two equivalent Co(2), two equivalent Co(3), and two equivalent Co(4) atoms to form distorted CoSmYCo10 cuboctahedra that share corners with four equivalent Co(1)Sm2YCo9 cuboctahedra, corners with four equivalent Co(2)SmY2Co9 cuboctahedra, corners with four equivalent Co(4)SmYCo10 cuboctahedra, corners with twelve equivalent Co(3)SmYCo10 cuboctahedra,  an edgeedge with one Co(1)Sm2YCo9 cuboctahedra,  an edgeedge with one Co(2)SmY2Co9 cuboctahedra,  an edgeedge with one Co(3)SmYCo10 cuboctahedra, edges with two equivalent Co(4)SmYCo10 cuboctahedra, faces with four equivalent Co(4)SmYCo10 cuboctahedra, faces with five equivalent Co(1)Sm2YCo9 cuboctahedra, faces with five equivalent Co(2)SmY2Co9 cuboctahedra, and faces with seven equivalent Co(3)SmYCo10 cuboctahedra. In the fourth Co site, Co(4) is bonded to one Sm(1), one Y(1), one Co(5), one Co(6), two equivalent Co(1), two equivalent Co(2), and four equivalent Co(3) atoms to form CoSmYCo10 cuboctahedra that share corners with four equivalent Co(4)SmYCo10 cuboctahedra, corners with five equivalent Co(1)Sm2YCo9 cuboctahedra, corners with five equivalent Co(2)SmY2Co9 cuboctahedra, corners with eight equivalent Co(3)SmYCo10 cuboctahedra, edges with three equivalent Co(1)Sm2YCo9 cuboctahedra, edges with three equivalent Co(2)SmY2Co9 cuboctahedra, edges with four equivalent Co(3)SmYCo10 cuboctahedra, faces with three equivalent Co(1)Sm2YCo9 cuboctahedra, faces with three equivalent Co(2)SmY2Co9 cuboctahedra, faces with four equivalent Co(4)SmYCo10 cuboctahedra, and faces with eight equivalent Co(3)SmYCo10 cuboctahedra. In the fifth Co site, Co(5) is bonded in a 14-coordinate geometry to one Y(1), one Co(6), three equivalent Co(2), three equivalent Co(4), and six equivalent Co(3) atoms. In the sixth Co site, Co(6) is bonded in a 14-coordinate geometry to one Sm(1), one Co(5), three equivalent Co(1), three equivalent Co(4), and six equivalent Co(3) atoms.
SmYCo17 crystallizes in the trigonal R3m space group. Sm(1) is bonded in a 19-coordinate geometry to one Co(6), three equivalent Co(2), three equivalent Co(4), six equivalent Co(1), and six equivalent Co(3) atoms. The Sm(1)-Co(6) bond length is 3.03 Å. All Sm(1)-Co(2) bond lengths are 2.99 Å. All Sm(1)-Co(4) bond lengths are 3.23 Å. There are three shorter (3.11 Å) and three longer (3.15 Å) Sm(1)-Co(1) bond lengths. All Sm(1)-Co(3) bond lengths are 2.97 Å. Y(1) is bonded in a 19-coordinate geometry to one Co(5), three equivalent Co(1), three equivalent Co(4), six equivalent Co(2), and six equivalent Co(3) atoms. The Y(1)-Co(5) bond length is 3.01 Å. All Y(1)-Co(1) bond lengths are 2.99 Å. All Y(1)-Co(4) bond lengths are 3.20 Å. There are three shorter (3.11 Å) and three longer (3.15 Å) Y(1)-Co(2) bond lengths. All Y(1)-Co(3) bond lengths are 2.97 Å. There are six inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent Sm(1), one Y(1), one Co(6), two equivalent Co(2), two equivalent Co(4), and four equivalent Co(3) atoms to form CoSm2YCo9 cuboctahedra that share corners with two equivalent Co(1)Sm2YCo9 cuboctahedra, corners with five equivalent Co(4)SmYCo10 cuboctahedra, corners with eight equivalent Co(2)SmY2Co9 cuboctahedra, corners with eight equivalent Co(3)SmYCo10 cuboctahedra,  an edgeedge with one Co(2)SmY2Co9 cuboctahedra, edges with two equivalent Co(3)SmYCo10 cuboctahedra, edges with three equivalent Co(4)SmYCo10 cuboctahedra, edges with four equivalent Co(1)Sm2YCo9 cuboctahedra, faces with three equivalent Co(2)SmY2Co9 cuboctahedra, faces with three equivalent Co(4)SmYCo10 cuboctahedra, faces with four equivalent Co(1)Sm2YCo9 cuboctahedra, and faces with ten equivalent Co(3)SmYCo10 cuboctahedra. The Co(1)-Co(6) bond length is 2.58 Å. Both Co(1)-Co(2) bond lengths are 2.43 Å. Both Co(1)-Co(4) bond lengths are 2.39 Å. There are two shorter (2.49 Å) and two longer (2.57 Å) Co(1)-Co(3) bond lengths. In the second Co site, Co(2) is bonded to one Sm(1), two equivalent Y(1), one Co(5), two equivalent Co(1), two equivalent Co(4), and four equivalent Co(3) atoms to form CoSmY2Co9 cuboctahedra that share corners with two equivalent Co(2)SmY2Co9 cuboctahedra, corners with five equivalent Co(4)SmYCo10 cuboctahedra, corners with eight equivalent Co(1)Sm2YCo9 cuboctahedra, corners with eight equivalent Co(3)SmYCo10 cuboctahedra,  an edgeedge with one Co(1)Sm2YCo9 cuboctahedra, edges with two equivalent Co(3)SmYCo10 cuboctahedra, edges with three equivalent Co(4)SmYCo10 cuboctahedra, edges with four equivalent Co(2)SmY2Co9 cuboctahedra, faces with three equivalent Co(1)Sm2YCo9 cuboctahedra, faces with three equivalent Co(4)SmYCo10 cuboctahedra, faces with four equivalent Co(2)SmY2Co9 cuboctahedra, and faces with ten equivalent Co(3)SmYCo10 cuboctahedra. The Co(2)-Co(5) bond length is 2.57 Å. Both Co(2)-Co(4) bond lengths are 2.38 Å. There are two shorter (2.47 Å) and two longer (2.58 Å) Co(2)-Co(3) bond lengths. In the third Co site, Co(3) is bonded to one Sm(1), one Y(1), one Co(5), one Co(6), two equivalent Co(1), two equivalent Co(2), two equivalent Co(3), and two equivalent Co(4) atoms to form distorted CoSmYCo10 cuboctahedra that share corners with four equivalent Co(1)Sm2YCo9 cuboctahedra, corners with four equivalent Co(2)SmY2Co9 cuboctahedra, corners with four equivalent Co(4)SmYCo10 cuboctahedra, corners with twelve equivalent Co(3)SmYCo10 cuboctahedra,  an edgeedge with one Co(1)Sm2YCo9 cuboctahedra,  an edgeedge with one Co(2)SmY2Co9 cuboctahedra,  an edgeedge with one Co(3)SmYCo10 cuboctahedra, edges with two equivalent Co(4)SmYCo10 cuboctahedra, faces with four equivalent Co(4)SmYCo10 cuboctahedra, faces with five equivalent Co(1)Sm2YCo9 cuboctahedra, faces with five equivalent Co(2)SmY2Co9 cuboctahedra, and faces with seven equivalent Co(3)SmYCo10 cuboctahedra. The Co(3)-Co(5) bond length is 2.65 Å. The Co(3)-Co(6) bond length is 2.65 Å. There is one shorter (2.39 Å) and one longer (2.40 Å) Co(3)-Co(3) bond length. There is one shorter (2.36 Å) and one longer (2.37 Å) Co(3)-Co(4) bond length. In the fourth Co site, Co(4) is bonded to one Sm(1), one Y(1), one Co(5), one Co(6), two equivalent Co(1), two equivalent Co(2), and four equivalent Co(3) atoms to form CoSmYCo10 cuboctahedra that share corners with four equivalent Co(4)SmYCo10 cuboctahedra, corners with five equivalent Co(1)Sm2YCo9 cuboctahedra, corners with five equivalent Co(2)SmY2Co9 cuboctahedra, corners with eight equivalent Co(3)SmYCo10 cuboctahedra, edges with three equivalent Co(1)Sm2YCo9 cuboctahedra, edges with three equivalent Co(2)SmY2Co9 cuboctahedra, edges with four equivalent Co(3)SmYCo10 cuboctahedra, faces with three equivalent Co(1)Sm2YCo9 cuboctahedra, faces with three equivalent Co(2)SmY2Co9 cuboctahedra, faces with four equivalent Co(4)SmYCo10 cuboctahedra, and faces with eight equivalent Co(3)SmYCo10 cuboctahedra. The Co(4)-Co(5) bond length is 2.55 Å. The Co(4)-Co(6) bond length is 2.55 Å. In the fifth Co site, Co(5) is bonded in a 14-coordinate geometry to one Y(1), one Co(6), three equivalent Co(2), three equivalent Co(4), and six equivalent Co(3) atoms. The Co(5)-Co(6) bond length is 2.28 Å. In the sixth Co site, Co(6) is bonded in a 14-coordinate geometry to one Sm(1), one Co(5), three equivalent Co(1), three equivalent Co(4), and six equivalent Co(3) atoms.