Dy2Fe17C2 crystallizes in the monoclinic C2/m space group. Dy(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 Dy(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 Dy(1), one Fe(1), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(5), and two equivalent Fe(7) atoms to form distorted FeDy3Fe9 cuboctahedra that share corners with two equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with three equivalent Fe(6)Dy2Fe10 cuboctahedra, corners with four equivalent Fe(2)Dy3Fe9 cuboctahedra, corners with four equivalent C(1)Dy2Fe4 octahedra,  an edgeedge with one Fe(6)Dy2Fe10 cuboctahedra,  an edgeedge with one Fe(2)Dy3Fe9 cuboctahedra, edges with two equivalent Fe(7)Dy2Fe10 cuboctahedra,  a faceface with one Fe(6)Dy2Fe10 cuboctahedra,  a faceface with one Fe(2)Dy3Fe9 cuboctahedra, faces with two equivalent Fe(7)Dy2Fe10 cuboctahedra, faces with four equivalent Fe(4)Dy2Fe10 cuboctahedra, and faces with two equivalent C(1)Dy2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 63-69°. 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 Dy(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 FeDy2Fe10 cuboctahedra that share corners with two equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(6)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(2)Dy3Fe9 cuboctahedra, corners with four equivalent C(1)Dy2Fe4 octahedra,  an edgeedge with one Fe(4)Dy2Fe10 cuboctahedra, edges with two equivalent Fe(7)Dy2Fe10 cuboctahedra, edges with two equivalent C(1)Dy2Fe4 octahedra,  a faceface with one Fe(4)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(6)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(7)Dy2Fe10 cuboctahedra, and faces with four equivalent Fe(2)Dy3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles range from 22-29°. 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 Dy(1), two equivalent Fe(1), four equivalent Fe(3), and four equivalent Fe(5) atoms to form distorted FeDy2Fe10 cuboctahedra that share corners with four equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with four equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with six equivalent Fe(2)Dy3Fe9 cuboctahedra, edges with two equivalent Fe(2)Dy3Fe9 cuboctahedra, faces with two equivalent Fe(2)Dy3Fe9 cuboctahedra, faces with four equivalent Fe(4)Dy2Fe10 cuboctahedra, faces with four equivalent Fe(7)Dy2Fe10 cuboctahedra, and faces with four equivalent C(1)Dy2Fe4 octahedra. In the seventh Fe site, Fe(7) is bonded to two equivalent Dy(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 FeDy2Fe10 cuboctahedra that share corners with two equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(6)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(2)Dy3Fe9 cuboctahedra, corners with two equivalent C(1)Dy2Fe4 octahedra, edges with two equivalent Fe(4)Dy2Fe10 cuboctahedra, edges with two equivalent Fe(2)Dy3Fe9 cuboctahedra, faces with two equivalent Fe(4)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(6)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(7)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(2)Dy3Fe9 cuboctahedra, and faces with two equivalent C(1)Dy2Fe4 octahedra. The corner-sharing octahedral tilt angles are 45°. C(1) is bonded to two equivalent Dy(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form CDy2Fe4 octahedra that share corners with two equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with four equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with four equivalent Fe(2)Dy3Fe9 cuboctahedra, corners with two equivalent C(1)Dy2Fe4 octahedra, edges with two equivalent Fe(4)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(6)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(7)Dy2Fe10 cuboctahedra, and faces with two equivalent Fe(2)Dy3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 62°.
Dy2Fe17C2 crystallizes in the monoclinic C2/m space group. Dy(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 Dy(1)-Fe(1) bond length is 3.06 Å. The Dy(1)-Fe(6) bond length is 3.35 Å. Both Dy(1)-Fe(4) bond lengths are 3.06 Å. Both Dy(1)-Fe(7) bond lengths are 3.29 Å. There are a spread of Dy(1)-Fe(2) bond distances ranging from 3.05-3.35 Å. Both Dy(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 Dy(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 2.66 Å. The Fe(1)-Fe(6) bond length is 2.64 Å. Both Fe(1)-Fe(3) bond lengths are 2.64 Å. Both Fe(1)-Fe(4) bond lengths are 2.73 Å. Both Fe(1)-Fe(7) bond lengths are 2.63 Å. There are two shorter (2.73 Å) and two longer (2.74 Å) Fe(1)-Fe(5) bond lengths. In the second Fe site, Fe(2) is bonded to three equivalent Dy(1), one Fe(1), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(5), and two equivalent Fe(7) atoms to form distorted FeDy3Fe9 cuboctahedra that share corners with two equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with three equivalent Fe(6)Dy2Fe10 cuboctahedra, corners with four equivalent Fe(2)Dy3Fe9 cuboctahedra, corners with four equivalent C(1)Dy2Fe4 octahedra,  an edgeedge with one Fe(6)Dy2Fe10 cuboctahedra,  an edgeedge with one Fe(2)Dy3Fe9 cuboctahedra, edges with two equivalent Fe(7)Dy2Fe10 cuboctahedra,  a faceface with one Fe(6)Dy2Fe10 cuboctahedra,  a faceface with one Fe(2)Dy3Fe9 cuboctahedra, faces with two equivalent Fe(7)Dy2Fe10 cuboctahedra, faces with four equivalent Fe(4)Dy2Fe10 cuboctahedra, and faces with two equivalent C(1)Dy2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 63-69°. Both Fe(2)-Fe(3) bond lengths are 2.55 Å. Both Fe(2)-Fe(4) bond lengths are 2.63 Å. Both Fe(2)-Fe(5) bond lengths are 2.57 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 2.47 Å. The Fe(3)-Fe(7) bond length is 2.47 Å. The Fe(3)-C(1) bond length is 1.91 Å. In the fourth Fe site, Fe(4) is bonded to two equivalent Dy(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 FeDy2Fe10 cuboctahedra that share corners with two equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(6)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(2)Dy3Fe9 cuboctahedra, corners with four equivalent C(1)Dy2Fe4 octahedra,  an edgeedge with one Fe(4)Dy2Fe10 cuboctahedra, edges with two equivalent Fe(7)Dy2Fe10 cuboctahedra, edges with two equivalent C(1)Dy2Fe4 octahedra,  a faceface with one Fe(4)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(6)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(7)Dy2Fe10 cuboctahedra, and faces with four equivalent Fe(2)Dy3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles range from 22-29°. Both Fe(4)-Fe(5) bond lengths are 2.47 Å. Both Fe(4)-Fe(7) bond lengths are 2.43 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 1.85 Å. In the sixth Fe site, Fe(6) is bonded to two equivalent Dy(1), two equivalent Fe(1), four equivalent Fe(3), and four equivalent Fe(5) atoms to form distorted FeDy2Fe10 cuboctahedra that share corners with four equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with four equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with six equivalent Fe(2)Dy3Fe9 cuboctahedra, edges with two equivalent Fe(2)Dy3Fe9 cuboctahedra, faces with two equivalent Fe(2)Dy3Fe9 cuboctahedra, faces with four equivalent Fe(4)Dy2Fe10 cuboctahedra, faces with four equivalent Fe(7)Dy2Fe10 cuboctahedra, and faces with four equivalent C(1)Dy2Fe4 octahedra. In the seventh Fe site, Fe(7) is bonded to two equivalent Dy(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 FeDy2Fe10 cuboctahedra that share corners with two equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(6)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with two equivalent Fe(2)Dy3Fe9 cuboctahedra, corners with two equivalent C(1)Dy2Fe4 octahedra, edges with two equivalent Fe(4)Dy2Fe10 cuboctahedra, edges with two equivalent Fe(2)Dy3Fe9 cuboctahedra, faces with two equivalent Fe(4)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(6)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(7)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(2)Dy3Fe9 cuboctahedra, and faces with two equivalent C(1)Dy2Fe4 octahedra. The corner-sharing octahedral tilt angles are 45°. C(1) is bonded to two equivalent Dy(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form CDy2Fe4 octahedra that share corners with two equivalent Fe(7)Dy2Fe10 cuboctahedra, corners with four equivalent Fe(4)Dy2Fe10 cuboctahedra, corners with four equivalent Fe(2)Dy3Fe9 cuboctahedra, corners with two equivalent C(1)Dy2Fe4 octahedra, edges with two equivalent Fe(4)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(6)Dy2Fe10 cuboctahedra, faces with two equivalent Fe(7)Dy2Fe10 cuboctahedra, and faces with two equivalent Fe(2)Dy3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 62°.