Tb2Fe17C2 crystallizes in the monoclinic C2/m space group. Tb(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 Tb(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 Tb(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 FeTb3Fe9 cuboctahedra that share corners with two equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with three equivalent Fe(6)Tb2Fe10 cuboctahedra, corners with four equivalent Fe(2)Tb3Fe9 cuboctahedra, corners with four equivalent C(1)Tb2Fe4 octahedra,  an edgeedge with one Fe(6)Tb2Fe10 cuboctahedra,  an edgeedge with one Fe(2)Tb3Fe9 cuboctahedra, edges with two equivalent Fe(7)Tb2Fe10 cuboctahedra,  a faceface with one Fe(6)Tb2Fe10 cuboctahedra,  a faceface with one Fe(2)Tb3Fe9 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with two equivalent C(1)Tb2Fe4 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 Tb(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 Tb(1), two equivalent Fe(1), four equivalent Fe(3), and four equivalent Fe(5) atoms to form distorted FeTb2Fe10 cuboctahedra that share corners with four equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with six equivalent Fe(2)Tb3Fe9 cuboctahedra, edges with two equivalent Fe(2)Tb3Fe9 cuboctahedra, faces with two equivalent Fe(2)Tb3Fe9 cuboctahedra, faces with four equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with four equivalent C(1)Tb2Fe4 octahedra. 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 two equivalent Fe(2)Tb3Fe9 cuboctahedra, corners with two equivalent C(1)Tb2Fe4 octahedra, edges with two equivalent Fe(2)Tb3Fe9 cuboctahedra, faces with two equivalent Fe(6)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(2)Tb3Fe9 cuboctahedra, and faces with two equivalent C(1)Tb2Fe4 octahedra. The corner-sharing octahedral tilt angles are 45°. C(1) is bonded to two equivalent Tb(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form CTb2Fe4 octahedra that share corners with two equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with four equivalent Fe(2)Tb3Fe9 cuboctahedra, corners with two equivalent C(1)Tb2Fe4 octahedra, faces with two equivalent Fe(6)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with two equivalent Fe(2)Tb3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 63°.
Tb2Fe17C2 crystallizes in the monoclinic C2/m space group. Tb(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 Tb(1)-Fe(1) bond length is 3.06 Å. The Tb(1)-Fe(6) bond length is 3.37 Å. Both Tb(1)-Fe(4) bond lengths are 3.07 Å. Both Tb(1)-Fe(7) bond lengths are 3.30 Å. There are a spread of Tb(1)-Fe(2) bond distances ranging from 3.05-3.37 Å. Both Tb(1)-C(1) bond lengths are 2.52 Å. There are seven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 14-coordinate geometry to one Tb(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 2.67 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 2.73 Å. Both Fe(1)-Fe(7) bond lengths are 2.64 Å. All Fe(1)-Fe(5) bond lengths are 2.75 Å. In the second Fe site, Fe(2) is bonded to three equivalent Tb(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 FeTb3Fe9 cuboctahedra that share corners with two equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with three equivalent Fe(6)Tb2Fe10 cuboctahedra, corners with four equivalent Fe(2)Tb3Fe9 cuboctahedra, corners with four equivalent C(1)Tb2Fe4 octahedra,  an edgeedge with one Fe(6)Tb2Fe10 cuboctahedra,  an edgeedge with one Fe(2)Tb3Fe9 cuboctahedra, edges with two equivalent Fe(7)Tb2Fe10 cuboctahedra,  a faceface with one Fe(6)Tb2Fe10 cuboctahedra,  a faceface with one Fe(2)Tb3Fe9 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with two equivalent C(1)Tb2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 63-69°. Both Fe(2)-Fe(3) bond lengths are 2.56 Å. Both Fe(2)-Fe(4) bond lengths are 2.64 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 2.57 Å. The Fe(3)-Fe(6) bond length is 2.48 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 Tb(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 2.48 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 2.44 Å. The Fe(5)-Fe(7) bond length is 2.44 Å. The Fe(5)-C(1) bond length is 1.85 Å. In the sixth Fe site, Fe(6) is bonded to two equivalent Tb(1), two equivalent Fe(1), four equivalent Fe(3), and four equivalent Fe(5) atoms to form distorted FeTb2Fe10 cuboctahedra that share corners with four equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with six equivalent Fe(2)Tb3Fe9 cuboctahedra, edges with two equivalent Fe(2)Tb3Fe9 cuboctahedra, faces with two equivalent Fe(2)Tb3Fe9 cuboctahedra, faces with four equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with four equivalent C(1)Tb2Fe4 octahedra. 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 two equivalent Fe(2)Tb3Fe9 cuboctahedra, corners with two equivalent C(1)Tb2Fe4 octahedra, edges with two equivalent Fe(2)Tb3Fe9 cuboctahedra, faces with two equivalent Fe(6)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(2)Tb3Fe9 cuboctahedra, and faces with two equivalent C(1)Tb2Fe4 octahedra. The corner-sharing octahedral tilt angles are 45°. C(1) is bonded to two equivalent Tb(1), two equivalent Fe(3), and two equivalent Fe(5) atoms to form CTb2Fe4 octahedra that share corners with two equivalent Fe(7)Tb2Fe10 cuboctahedra, corners with four equivalent Fe(2)Tb3Fe9 cuboctahedra, corners with two equivalent C(1)Tb2Fe4 octahedra, faces with two equivalent Fe(6)Tb2Fe10 cuboctahedra, faces with two equivalent Fe(7)Tb2Fe10 cuboctahedra, and faces with two equivalent Fe(2)Tb3Fe9 cuboctahedra. The corner-sharing octahedral tilt angles are 63°.