Ho2Fe17C2 crystallizes in the monoclinic C2/m space group. Ho(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 Ho(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 Ho(1), one Fe(1), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(5), and two equivalent Fe(7) atoms to form FeHo3Fe9 cuboctahedra that share corners with two equivalent Fe(7)Ho2Fe10 cuboctahedra, corners with three equivalent Fe(6)Ho2Fe10 cuboctahedra, corners with four equivalent Fe(2)Ho3Fe9 cuboctahedra, corners with four equivalent C(1)Ho2Fe4 octahedra,  an edgeedge with one Fe(6)Ho2Fe10 cuboctahedra,  an edgeedge with one Fe(2)Ho3Fe9 cuboctahedra, edges with two equivalent Fe(7)Ho2Fe10 cuboctahedra,  a faceface with one Fe(6)Ho2Fe10 cuboctahedra,  a faceface with one Fe(2)Ho3Fe9 cuboctahedra, faces with two equivalent Fe(7)Ho2Fe10 cuboctahedra, and faces with two equivalent C(1)Ho2Fe4 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 in a 12-coordinate geometry to two equivalent Ho(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(5), and two equivalent Fe(7) atoms. 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 Ho(1), two equivalent Fe(1), four equivalent Fe(3), and four equivalent Fe(5) atoms to form distorted FeHo2Fe10 cuboctahedra that share corners with four equivalent Fe(7)Ho2Fe10 cuboctahedra, corners with six equivalent Fe(2)Ho3Fe9 cuboctahedra, edges with two equivalent Fe(2)Ho3Fe9 cuboctahedra, faces with two equivalent Fe(2)Ho3Fe9 cuboctahedra, faces with four equivalent Fe(7)Ho2Fe10 cuboctahedra, and faces with four equivalent C(1)Ho2Fe4 octahedra. In the seventh Fe site, Fe(7) is bonded to two equivalent Ho(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 FeHo2Fe10 cuboctahedra that share corners with two equivalent Fe(6)Ho2Fe10 cuboctahedra, corners with two equivalent Fe(7)Ho2Fe10 cuboctahedra, corners with two equivalent Fe(2)Ho3Fe9 cuboctahedra, corners with two equivalent C(1)Ho2Fe4 octahedra, edges with two equivalent Fe(2)Ho3Fe9 cuboctahedra, faces with two equivalent Fe(6)Ho2Fe10 cuboctahedra, faces with two equivalent Fe(7)Ho2Fe10 cuboctahedra, faces with two equivalent Fe(2)Ho3Fe9 cuboctahedra, and faces with two equivalent C(1)Ho2Fe4 octahedra. The corner-sharing octahedral tilt angles are 45°. C(1) is bonded to two equivalent Ho(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form CHo2Fe4 octahedra that share corners with two equivalent Fe(7)Ho2Fe10 cuboctahedra, corners with four equivalent Fe(2)Ho3Fe9 cuboctahedra, corners with two equivalent C(1)Ho2Fe4 octahedra, faces with two equivalent Fe(6)Ho2Fe10 cuboctahedra, faces with two equivalent Fe(7)Ho2Fe10 cuboctahedra, and faces with two equivalent Fe(2)Ho3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 62°.
Ho2Fe17C2 crystallizes in the monoclinic C2/m space group. Ho(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 Ho(1)-Fe(1) bond length is 3.06 Å. The Ho(1)-Fe(6) bond length is 3.35 Å. Both Ho(1)-Fe(4) bond lengths are 3.07 Å. Both Ho(1)-Fe(7) bond lengths are 3.30 Å. There are a spread of Ho(1)-Fe(2) bond distances ranging from 3.05-3.35 Å. Both Ho(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 Ho(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 2.40 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. All Fe(1)-Fe(5) bond lengths are 2.73 Å. In the second Fe site, Fe(2) is bonded to three equivalent Ho(1), one Fe(1), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(5), and two equivalent Fe(7) atoms to form FeHo3Fe9 cuboctahedra that share corners with two equivalent Fe(7)Ho2Fe10 cuboctahedra, corners with three equivalent Fe(6)Ho2Fe10 cuboctahedra, corners with four equivalent Fe(2)Ho3Fe9 cuboctahedra, corners with four equivalent C(1)Ho2Fe4 octahedra,  an edgeedge with one Fe(6)Ho2Fe10 cuboctahedra,  an edgeedge with one Fe(2)Ho3Fe9 cuboctahedra, edges with two equivalent Fe(7)Ho2Fe10 cuboctahedra,  a faceface with one Fe(6)Ho2Fe10 cuboctahedra,  a faceface with one Fe(2)Ho3Fe9 cuboctahedra, faces with two equivalent Fe(7)Ho2Fe10 cuboctahedra, and faces with two equivalent C(1)Ho2Fe4 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 2.58 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 in a 12-coordinate geometry to two equivalent Ho(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(5), and two equivalent Fe(7) atoms. Both Fe(4)-Fe(5) bond lengths are 2.46 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 1.86 Å. In the sixth Fe site, Fe(6) is bonded to two equivalent Ho(1), two equivalent Fe(1), four equivalent Fe(3), and four equivalent Fe(5) atoms to form distorted FeHo2Fe10 cuboctahedra that share corners with four equivalent Fe(7)Ho2Fe10 cuboctahedra, corners with six equivalent Fe(2)Ho3Fe9 cuboctahedra, edges with two equivalent Fe(2)Ho3Fe9 cuboctahedra, faces with two equivalent Fe(2)Ho3Fe9 cuboctahedra, faces with four equivalent Fe(7)Ho2Fe10 cuboctahedra, and faces with four equivalent C(1)Ho2Fe4 octahedra. In the seventh Fe site, Fe(7) is bonded to two equivalent Ho(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 FeHo2Fe10 cuboctahedra that share corners with two equivalent Fe(6)Ho2Fe10 cuboctahedra, corners with two equivalent Fe(7)Ho2Fe10 cuboctahedra, corners with two equivalent Fe(2)Ho3Fe9 cuboctahedra, corners with two equivalent C(1)Ho2Fe4 octahedra, edges with two equivalent Fe(2)Ho3Fe9 cuboctahedra, faces with two equivalent Fe(6)Ho2Fe10 cuboctahedra, faces with two equivalent Fe(7)Ho2Fe10 cuboctahedra, faces with two equivalent Fe(2)Ho3Fe9 cuboctahedra, and faces with two equivalent C(1)Ho2Fe4 octahedra. The corner-sharing octahedral tilt angles are 45°. C(1) is bonded to two equivalent Ho(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form CHo2Fe4 octahedra that share corners with two equivalent Fe(7)Ho2Fe10 cuboctahedra, corners with four equivalent Fe(2)Ho3Fe9 cuboctahedra, corners with two equivalent C(1)Ho2Fe4 octahedra, faces with two equivalent Fe(6)Ho2Fe10 cuboctahedra, faces with two equivalent Fe(7)Ho2Fe10 cuboctahedra, and faces with two equivalent Fe(2)Ho3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 62°.