Y2Fe17C2 crystallizes in the monoclinic C2/m space group. Y(1) is bonded in a distorted bent 120 degrees geometry to one Fe(1), one Fe(6), two equivalent Fe(4), two equivalent Fe(7), three equivalent Fe(2), and two equivalent C(1) atoms. There are seven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 14-coordinate geometry to one Y(1), one Fe(1), one Fe(2), one Fe(6), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(7), and four equivalent Fe(5) atoms. In the second Fe site, Fe(2) is bonded to three equivalent Y(1), one Fe(1), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(5), and two equivalent Fe(7) atoms to form FeY3Fe9 cuboctahedra that share corners with two equivalent Fe(4)Y2Fe10 cuboctahedra, corners with two equivalent Fe(7)Y2Fe10 cuboctahedra, corners with three equivalent Fe(6)Y2Fe10 cuboctahedra, corners with four equivalent Fe(2)Y3Fe9 cuboctahedra, corners with four equivalent C(1)Y2Fe4 octahedra,  an edgeedge with one Fe(6)Y2Fe10 cuboctahedra,  an edgeedge with one Fe(2)Y3Fe9 cuboctahedra, edges with two equivalent Fe(7)Y2Fe10 cuboctahedra,  a faceface with one Fe(6)Y2Fe10 cuboctahedra,  a faceface with one Fe(2)Y3Fe9 cuboctahedra, faces with two equivalent Fe(7)Y2Fe10 cuboctahedra, faces with four equivalent Fe(4)Y2Fe10 cuboctahedra, and faces with two equivalent C(1)Y2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 64-69°. In the third Fe site, Fe(3) is bonded in a single-bond geometry to one Fe(1), one Fe(2), one Fe(4), one Fe(6), one Fe(7), and one C(1) atom. In the fourth Fe site, Fe(4) is bonded to two equivalent Y(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(5), and two equivalent Fe(7) atoms to form distorted FeY2Fe10 cuboctahedra that share corners with two equivalent Fe(4)Y2Fe10 cuboctahedra, corners with two equivalent Fe(6)Y2Fe10 cuboctahedra, corners with two equivalent Fe(7)Y2Fe10 cuboctahedra, corners with two equivalent Fe(2)Y3Fe9 cuboctahedra, corners with four equivalent C(1)Y2Fe4 octahedra,  an edgeedge with one Fe(4)Y2Fe10 cuboctahedra, edges with two equivalent Fe(7)Y2Fe10 cuboctahedra, edges with two equivalent C(1)Y2Fe4 octahedra,  a faceface with one Fe(4)Y2Fe10 cuboctahedra, faces with two equivalent Fe(6)Y2Fe10 cuboctahedra, faces with two equivalent Fe(7)Y2Fe10 cuboctahedra, and faces with four equivalent Fe(2)Y3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles range from 23-29°. In the fifth Fe site, Fe(5) is bonded in a single-bond geometry to one Fe(2), one Fe(4), one Fe(6), one Fe(7), two equivalent Fe(1), and one C(1) atom. In the sixth Fe site, Fe(6) is bonded to two equivalent Y(1), two equivalent Fe(1), four equivalent Fe(3), and four equivalent Fe(5) atoms to form distorted FeY2Fe10 cuboctahedra that share corners with four equivalent Fe(4)Y2Fe10 cuboctahedra, corners with four equivalent Fe(7)Y2Fe10 cuboctahedra, corners with six equivalent Fe(2)Y3Fe9 cuboctahedra, edges with two equivalent Fe(2)Y3Fe9 cuboctahedra, faces with two equivalent Fe(2)Y3Fe9 cuboctahedra, faces with four equivalent Fe(4)Y2Fe10 cuboctahedra, faces with four equivalent Fe(7)Y2Fe10 cuboctahedra, and faces with four equivalent C(1)Y2Fe4 octahedra. In the seventh Fe site, Fe(7) is bonded to two equivalent Y(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(4), and two equivalent Fe(5) atoms to form FeY2Fe10 cuboctahedra that share corners with two equivalent Fe(4)Y2Fe10 cuboctahedra, corners with two equivalent Fe(6)Y2Fe10 cuboctahedra, corners with two equivalent Fe(7)Y2Fe10 cuboctahedra, corners with two equivalent Fe(2)Y3Fe9 cuboctahedra, corners with two equivalent C(1)Y2Fe4 octahedra, edges with two equivalent Fe(4)Y2Fe10 cuboctahedra, edges with two equivalent Fe(2)Y3Fe9 cuboctahedra, faces with two equivalent Fe(4)Y2Fe10 cuboctahedra, faces with two equivalent Fe(6)Y2Fe10 cuboctahedra, faces with two equivalent Fe(7)Y2Fe10 cuboctahedra, faces with two equivalent Fe(2)Y3Fe9 cuboctahedra, and faces with two equivalent C(1)Y2Fe4 octahedra. The corner-sharing octahedral tilt angles are 44°. C(1) is bonded to two equivalent Y(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form CY2Fe4 octahedra that share corners with two equivalent Fe(7)Y2Fe10 cuboctahedra, corners with four equivalent Fe(4)Y2Fe10 cuboctahedra, corners with four equivalent Fe(2)Y3Fe9 cuboctahedra, corners with two equivalent C(1)Y2Fe4 octahedra, edges with two equivalent Fe(4)Y2Fe10 cuboctahedra, faces with two equivalent Fe(6)Y2Fe10 cuboctahedra, faces with two equivalent Fe(7)Y2Fe10 cuboctahedra, and faces with two equivalent Fe(2)Y3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 62°.
Y2Fe17C2 crystallizes in the monoclinic C2/m space group. Y(1) is bonded in a distorted bent 120 degrees geometry to one Fe(1), one Fe(6), two equivalent Fe(4), two equivalent Fe(7), three equivalent Fe(2), and two equivalent C(1) atoms. The Y(1)-Fe(1) bond length is 3.06 Å. The Y(1)-Fe(6) bond length is 3.35 Å. Both Y(1)-Fe(4) bond lengths are 3.06 Å. Both Y(1)-Fe(7) bond lengths are 3.30 Å. There are a spread of Y(1)-Fe(2) bond distances ranging from 3.08-3.33 Å. Both Y(1)-C(1) bond lengths are 2.51 Å. There are seven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 14-coordinate geometry to one Y(1), one Fe(1), one Fe(2), one Fe(6), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(7), and four equivalent Fe(5) atoms. The Fe(1)-Fe(1) bond length is 2.39 Å. The Fe(1)-Fe(2) bond length is 2.67 Å. The Fe(1)-Fe(6) bond length is 2.65 Å. Both Fe(1)-Fe(3) bond lengths are 2.65 Å. Both Fe(1)-Fe(4) bond lengths are 2.75 Å. Both Fe(1)-Fe(7) bond lengths are 2.63 Å. All Fe(1)-Fe(5) bond lengths are 2.74 Å. In the second Fe site, Fe(2) is bonded to three equivalent Y(1), one Fe(1), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(5), and two equivalent Fe(7) atoms to form FeY3Fe9 cuboctahedra that share corners with two equivalent Fe(4)Y2Fe10 cuboctahedra, corners with two equivalent Fe(7)Y2Fe10 cuboctahedra, corners with three equivalent Fe(6)Y2Fe10 cuboctahedra, corners with four equivalent Fe(2)Y3Fe9 cuboctahedra, corners with four equivalent C(1)Y2Fe4 octahedra,  an edgeedge with one Fe(6)Y2Fe10 cuboctahedra,  an edgeedge with one Fe(2)Y3Fe9 cuboctahedra, edges with two equivalent Fe(7)Y2Fe10 cuboctahedra,  a faceface with one Fe(6)Y2Fe10 cuboctahedra,  a faceface with one Fe(2)Y3Fe9 cuboctahedra, faces with two equivalent Fe(7)Y2Fe10 cuboctahedra, faces with four equivalent Fe(4)Y2Fe10 cuboctahedra, and faces with two equivalent C(1)Y2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 64-69°. Both Fe(2)-Fe(3) bond lengths are 2.54 Å. Both Fe(2)-Fe(4) bond lengths are 2.63 Å. Both Fe(2)-Fe(5) bond lengths are 2.56 Å. Both Fe(2)-Fe(7) bond lengths are 2.47 Å. In the third Fe site, Fe(3) is bonded in a single-bond geometry to one Fe(1), one Fe(2), one Fe(4), one Fe(6), one Fe(7), and one C(1) atom. The Fe(3)-Fe(4) bond length is 2.56 Å. The Fe(3)-Fe(6) bond length is 2.48 Å. The Fe(3)-Fe(7) bond length is 2.48 Å. The Fe(3)-C(1) bond length is 1.92 Å. In the fourth Fe site, Fe(4) is bonded to two equivalent Y(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(5), and two equivalent Fe(7) atoms to form distorted FeY2Fe10 cuboctahedra that share corners with two equivalent Fe(4)Y2Fe10 cuboctahedra, corners with two equivalent Fe(6)Y2Fe10 cuboctahedra, corners with two equivalent Fe(7)Y2Fe10 cuboctahedra, corners with two equivalent Fe(2)Y3Fe9 cuboctahedra, corners with four equivalent C(1)Y2Fe4 octahedra,  an edgeedge with one Fe(4)Y2Fe10 cuboctahedra, edges with two equivalent Fe(7)Y2Fe10 cuboctahedra, edges with two equivalent C(1)Y2Fe4 octahedra,  a faceface with one Fe(4)Y2Fe10 cuboctahedra, faces with two equivalent Fe(6)Y2Fe10 cuboctahedra, faces with two equivalent Fe(7)Y2Fe10 cuboctahedra, and faces with four equivalent Fe(2)Y3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles range from 23-29°. Both Fe(4)-Fe(5) bond lengths are 2.48 Å. Both Fe(4)-Fe(7) bond lengths are 2.44 Å. In the fifth Fe site, Fe(5) is bonded in a single-bond geometry to one Fe(2), one Fe(4), one Fe(6), one Fe(7), two equivalent Fe(1), and one C(1) atom. The Fe(5)-Fe(6) bond length is 2.43 Å. The Fe(5)-Fe(7) bond length is 2.43 Å. The Fe(5)-C(1) bond length is 1.86 Å. In the sixth Fe site, Fe(6) is bonded to two equivalent Y(1), two equivalent Fe(1), four equivalent Fe(3), and four equivalent Fe(5) atoms to form distorted FeY2Fe10 cuboctahedra that share corners with four equivalent Fe(4)Y2Fe10 cuboctahedra, corners with four equivalent Fe(7)Y2Fe10 cuboctahedra, corners with six equivalent Fe(2)Y3Fe9 cuboctahedra, edges with two equivalent Fe(2)Y3Fe9 cuboctahedra, faces with two equivalent Fe(2)Y3Fe9 cuboctahedra, faces with four equivalent Fe(4)Y2Fe10 cuboctahedra, faces with four equivalent Fe(7)Y2Fe10 cuboctahedra, and faces with four equivalent C(1)Y2Fe4 octahedra. In the seventh Fe site, Fe(7) is bonded to two equivalent Y(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(4), and two equivalent Fe(5) atoms to form FeY2Fe10 cuboctahedra that share corners with two equivalent Fe(4)Y2Fe10 cuboctahedra, corners with two equivalent Fe(6)Y2Fe10 cuboctahedra, corners with two equivalent Fe(7)Y2Fe10 cuboctahedra, corners with two equivalent Fe(2)Y3Fe9 cuboctahedra, corners with two equivalent C(1)Y2Fe4 octahedra, edges with two equivalent Fe(4)Y2Fe10 cuboctahedra, edges with two equivalent Fe(2)Y3Fe9 cuboctahedra, faces with two equivalent Fe(4)Y2Fe10 cuboctahedra, faces with two equivalent Fe(6)Y2Fe10 cuboctahedra, faces with two equivalent Fe(7)Y2Fe10 cuboctahedra, faces with two equivalent Fe(2)Y3Fe9 cuboctahedra, and faces with two equivalent C(1)Y2Fe4 octahedra. The corner-sharing octahedral tilt angles are 44°. C(1) is bonded to two equivalent Y(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form CY2Fe4 octahedra that share corners with two equivalent Fe(7)Y2Fe10 cuboctahedra, corners with four equivalent Fe(4)Y2Fe10 cuboctahedra, corners with four equivalent Fe(2)Y3Fe9 cuboctahedra, corners with two equivalent C(1)Y2Fe4 octahedra, edges with two equivalent Fe(4)Y2Fe10 cuboctahedra, faces with two equivalent Fe(6)Y2Fe10 cuboctahedra, faces with two equivalent Fe(7)Y2Fe10 cuboctahedra, and faces with two equivalent Fe(2)Y3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 62°.