Tb2Fe17C crystallizes in the monoclinic C2/m space group. Tb(1) is bonded in a distorted single-bond geometry to one Fe(5), one Fe(6), two equivalent Fe(7), four equivalent Fe(2), six equivalent Fe(4), and one C(1) atom. There are seven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a single-bond geometry to two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(5), two equivalent Fe(7), and one C(1) atom. In the second Fe site, Fe(2) is bonded in a 12-coordinate geometry to two equivalent Tb(1), one Fe(1), one Fe(2), one Fe(3), one Fe(6), one Fe(7), two equivalent Fe(5), and three equivalent Fe(4) atoms. In the third Fe site, Fe(3) is bonded in a single-bond geometry to one Fe(5), two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(7), and one C(1) atom. In the fourth Fe site, Fe(4) is bonded to three equivalent Tb(1), one Fe(1), one Fe(3), one Fe(4), one Fe(5), one Fe(6), one Fe(7), and three equivalent Fe(2) atoms to form FeTb3Fe9 cuboctahedra that share  a cornercorner with one Fe(6)Tb2Fe10 cuboctahedra, corners with four equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with seven equivalent Fe(4)Tb3Fe9 cuboctahedra, corners with two equivalent C(1)Tb2Fe4 octahedra,  an edgeedge with one Fe(6)Tb2Fe10 cuboctahedra, edges with two equivalent Fe(7)Tb2Fe10 cuboctahedra, edges with three equivalent Fe(4)Tb3Fe9 cuboctahedra,  a faceface with one Fe(6)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, faces with four equivalent Fe(4)Tb3Fe9 cuboctahedra, and  a faceface with one C(1)Tb2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 65-70°. In the fifth Fe site, Fe(5) is bonded in a 14-coordinate geometry to one Tb(1), one Fe(3), one Fe(5), one Fe(6), two equivalent Fe(1), two equivalent Fe(4), two equivalent Fe(7), and four equivalent Fe(2) atoms. In the sixth Fe site, Fe(6) is bonded to two equivalent Tb(1), two equivalent Fe(5), four equivalent Fe(2), and four equivalent Fe(4) atoms to form FeTb2Fe10 cuboctahedra that share corners with four equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with four equivalent Fe(4)Tb3Fe9 cuboctahedra, corners with two equivalent C(1)Tb2Fe4 octahedra, edges with four equivalent Fe(4)Tb3Fe9 cuboctahedra, faces with four equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with four equivalent Fe(4)Tb3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 45°. In the seventh Fe site, Fe(7) is bonded to two equivalent Tb(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 FeTb2Fe10 cuboctahedra that share corners with two equivalent Fe(6)Tb2Fe10 cuboctahedra, corners with two equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with eight equivalent Fe(4)Tb3Fe9 cuboctahedra, edges with four equivalent Fe(4)Tb3Fe9 cuboctahedra, faces with two equivalent Fe(6)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, faces with four equivalent Fe(4)Tb3Fe9 cuboctahedra, and faces with two equivalent C(1)Tb2Fe4 octahedra. C(1) is bonded to two equivalent Tb(1), two equivalent Fe(1), and two equivalent Fe(3) atoms to form CTb2Fe4 octahedra that share corners with two equivalent Fe(6)Tb2Fe10 cuboctahedra, corners with eight equivalent Fe(4)Tb3Fe9 cuboctahedra, faces with four equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with four equivalent Fe(4)Tb3Fe9 cuboctahedra.
Tb2Fe17C crystallizes in the monoclinic C2/m space group. Tb(1) is bonded in a distorted single-bond geometry to one Fe(5), one Fe(6), two equivalent Fe(7), four equivalent Fe(2), six equivalent Fe(4), and one C(1) atom. The Tb(1)-Fe(5) bond length is 3.04 Å. The Tb(1)-Fe(6) bond length is 3.26 Å. Both Tb(1)-Fe(7) bond lengths are 3.32 Å. There are two shorter (3.01 Å) and two longer (3.08 Å) Tb(1)-Fe(2) bond lengths. There are a spread of Tb(1)-Fe(4) bond distances ranging from 3.06-3.29 Å. The Tb(1)-C(1) bond length is 2.53 Å. There are seven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a single-bond geometry to two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(5), two equivalent Fe(7), and one C(1) atom. Both Fe(1)-Fe(2) bond lengths are 2.46 Å. Both Fe(1)-Fe(4) bond lengths are 2.55 Å. Both Fe(1)-Fe(5) bond lengths are 2.73 Å. Both Fe(1)-Fe(7) bond lengths are 2.42 Å. The Fe(1)-C(1) bond length is 1.84 Å. In the second Fe site, Fe(2) is bonded in a 12-coordinate geometry to two equivalent Tb(1), one Fe(1), one Fe(2), one Fe(3), one Fe(6), one Fe(7), two equivalent Fe(5), and three equivalent Fe(4) atoms. The Fe(2)-Fe(2) bond length is 2.49 Å. The Fe(2)-Fe(3) bond length is 2.56 Å. The Fe(2)-Fe(6) bond length is 2.43 Å. The Fe(2)-Fe(7) bond length is 2.43 Å. Both Fe(2)-Fe(5) bond lengths are 2.76 Å. There are a spread of Fe(2)-Fe(4) bond distances ranging from 2.55-2.63 Å. In the third Fe site, Fe(3) is bonded in a single-bond geometry to one Fe(5), two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(7), and one C(1) atom. The Fe(3)-Fe(5) bond length is 2.64 Å. Both Fe(3)-Fe(4) bond lengths are 2.53 Å. Both Fe(3)-Fe(7) bond lengths are 2.47 Å. The Fe(3)-C(1) bond length is 1.91 Å. In the fourth Fe site, Fe(4) is bonded to three equivalent Tb(1), one Fe(1), one Fe(3), one Fe(4), one Fe(5), one Fe(6), one Fe(7), and three equivalent Fe(2) atoms to form FeTb3Fe9 cuboctahedra that share  a cornercorner with one Fe(6)Tb2Fe10 cuboctahedra, corners with four equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with seven equivalent Fe(4)Tb3Fe9 cuboctahedra, corners with two equivalent C(1)Tb2Fe4 octahedra,  an edgeedge with one Fe(6)Tb2Fe10 cuboctahedra, edges with two equivalent Fe(7)Tb2Fe10 cuboctahedra, edges with three equivalent Fe(4)Tb3Fe9 cuboctahedra,  a faceface with one Fe(6)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, faces with four equivalent Fe(4)Tb3Fe9 cuboctahedra, and  a faceface with one C(1)Tb2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 65-70°. The Fe(4)-Fe(4) bond length is 2.51 Å. The Fe(4)-Fe(5) bond length is 2.65 Å. The Fe(4)-Fe(6) bond length is 2.46 Å. The Fe(4)-Fe(7) bond length is 2.46 Å. In the fifth Fe site, Fe(5) is bonded in a 14-coordinate geometry to one Tb(1), one Fe(3), one Fe(5), one Fe(6), two equivalent Fe(1), two equivalent Fe(4), two equivalent Fe(7), and four equivalent Fe(2) atoms. The Fe(5)-Fe(5) bond length is 2.41 Å. The Fe(5)-Fe(6) bond length is 2.61 Å. Both Fe(5)-Fe(7) bond lengths are 2.62 Å. In the sixth Fe site, Fe(6) is bonded to two equivalent Tb(1), two equivalent Fe(5), four equivalent Fe(2), and four equivalent Fe(4) atoms to form FeTb2Fe10 cuboctahedra that share corners with four equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with four equivalent Fe(4)Tb3Fe9 cuboctahedra, corners with two equivalent C(1)Tb2Fe4 octahedra, edges with four equivalent Fe(4)Tb3Fe9 cuboctahedra, faces with four equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with four equivalent Fe(4)Tb3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 45°. In the seventh Fe site, Fe(7) is bonded to two equivalent Tb(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 FeTb2Fe10 cuboctahedra that share corners with two equivalent Fe(6)Tb2Fe10 cuboctahedra, corners with two equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with eight equivalent Fe(4)Tb3Fe9 cuboctahedra, edges with four equivalent Fe(4)Tb3Fe9 cuboctahedra, faces with two equivalent Fe(6)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, faces with four equivalent Fe(4)Tb3Fe9 cuboctahedra, and faces with two equivalent C(1)Tb2Fe4 octahedra. C(1) is bonded to two equivalent Tb(1), two equivalent Fe(1), and two equivalent Fe(3) atoms to form CTb2Fe4 octahedra that share corners with two equivalent Fe(6)Tb2Fe10 cuboctahedra, corners with eight equivalent Fe(4)Tb3Fe9 cuboctahedra, faces with four equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with four equivalent Fe(4)Tb3Fe9 cuboctahedra.