Ce2Fe20Si2C crystallizes in the triclinic P-1 space group. Ce(1) is bonded in a distorted single-bond geometry to one Fe(10), one Fe(11), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(5), two equivalent Fe(8), two equivalent Fe(9), and one C(1) atom. There are eleven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 14-coordinate geometry to two equivalent Ce(1), one Fe(10), one Fe(11), one Fe(2), one Fe(3), one Fe(4), one Fe(5), one Fe(6), one Fe(7), one Fe(8), one Fe(9), one Si(1), and one Si(2) atom. In the second Fe site, Fe(2) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(11), one Fe(4), one Fe(5), one Fe(6), one Fe(8), one Fe(9), two equivalent Fe(3), and one Si(2) atom. In the third Fe site, Fe(3) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(4), one Fe(5), one Fe(7), one Fe(8), one Fe(9), two equivalent Fe(2), one Si(1), and one Si(2) atom. In the fourth Fe site, Fe(4) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(10), one Fe(2), one Fe(3), one Fe(5), one Fe(6), one Fe(7), two equivalent Fe(8), and one Si(1) atom. In the fifth Fe site, Fe(5) is bonded to two equivalent Ce(1), one Fe(1), one Fe(10), one Fe(11), one Fe(2), one Fe(3), one Fe(4), one Fe(6), one Fe(7), and two equivalent Fe(9) atoms to form distorted FeCe2Fe10 cuboctahedra that share  a cornercorner with one Fe(10)Ce2Fe10 cuboctahedra, corners with two equivalent Fe(5)Ce2Fe10 cuboctahedra, corners with two equivalent C(1)Ce2Fe4 octahedra,  an edgeedge with one C(1)Ce2Fe4 octahedra,  a faceface with one Fe(10)Ce2Fe10 cuboctahedra, and  a faceface with one Fe(5)Ce2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles range from 28-71°. In the sixth Fe site, Fe(6) is bonded in a single-bond geometry to one Fe(1), one Fe(10), one Fe(11), one Fe(2), one Fe(4), one Fe(5), one Fe(8), one Fe(9), and one C(1) atom. In the seventh Fe site, Fe(7) is bonded in a single-bond geometry to one Fe(1), one Fe(10), one Fe(3), one Fe(4), one Fe(5), one Fe(8), one Fe(9), one Si(1), and one C(1) atom. In the eighth Fe site, Fe(8) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(2), one Fe(3), one Fe(6), one Fe(7), one Fe(9), two equivalent Fe(4), one Si(1), and one Si(2) atom. In the ninth Fe site, Fe(9) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(11), one Fe(2), one Fe(3), one Fe(6), one Fe(7), one Fe(8), two equivalent Fe(5), and one Si(2) atom. In the tenth Fe site, Fe(10) is bonded to two equivalent Ce(1), two equivalent Fe(1), two equivalent Fe(4), two equivalent Fe(5), two equivalent Fe(6), and two equivalent Fe(7) atoms to form distorted FeCe2Fe10 cuboctahedra that share corners with two equivalent Fe(5)Ce2Fe10 cuboctahedra, faces with two equivalent Fe(5)Ce2Fe10 cuboctahedra, and faces with two equivalent C(1)Ce2Fe4 octahedra. In the eleventh Fe site, Fe(11) is bonded in a 12-coordinate geometry to two equivalent Ce(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(5), two equivalent Fe(6), and two equivalent Fe(9) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to two equivalent Fe(1), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(7), and two equivalent Fe(8) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(8), and two equivalent Fe(9) atoms. C(1) is bonded to two equivalent Ce(1), two equivalent Fe(6), and two equivalent Fe(7) atoms to form CCe2Fe4 octahedra that share corners with four equivalent Fe(5)Ce2Fe10 cuboctahedra, edges with two equivalent Fe(5)Ce2Fe10 cuboctahedra, and faces with two equivalent Fe(10)Ce2Fe10 cuboctahedra.
Ce2Fe20Si2C crystallizes in the triclinic P-1 space group. Ce(1) is bonded in a distorted single-bond geometry to one Fe(10), one Fe(11), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(5), two equivalent Fe(8), two equivalent Fe(9), and one C(1) atom. The Ce(1)-Fe(10) bond length is 3.45 Å. The Ce(1)-Fe(11) bond length is 3.48 Å. There is one shorter (3.15 Å) and one longer (3.22 Å) Ce(1)-Fe(1) bond length. There is one shorter (3.07 Å) and one longer (3.18 Å) Ce(1)-Fe(2) bond length. There is one shorter (3.11 Å) and one longer (3.18 Å) Ce(1)-Fe(3) bond length. There is one shorter (3.12 Å) and one longer (3.23 Å) Ce(1)-Fe(4) bond length. There is one shorter (3.10 Å) and one longer (3.20 Å) Ce(1)-Fe(5) bond length. There is one shorter (3.10 Å) and one longer (3.33 Å) Ce(1)-Fe(8) bond length. There is one shorter (3.09 Å) and one longer (3.33 Å) Ce(1)-Fe(9) bond length. The Ce(1)-C(1) bond length is 2.63 Å. There are eleven inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 14-coordinate geometry to two equivalent Ce(1), one Fe(10), one Fe(11), one Fe(2), one Fe(3), one Fe(4), one Fe(5), one Fe(6), one Fe(7), one Fe(8), one Fe(9), one Si(1), and one Si(2) atom. The Fe(1)-Fe(10) bond length is 2.61 Å. The Fe(1)-Fe(11) bond length is 2.68 Å. The Fe(1)-Fe(2) bond length is 2.67 Å. The Fe(1)-Fe(3) bond length is 2.66 Å. The Fe(1)-Fe(4) bond length is 2.71 Å. The Fe(1)-Fe(5) bond length is 2.73 Å. The Fe(1)-Fe(6) bond length is 2.71 Å. The Fe(1)-Fe(7) bond length is 2.66 Å. The Fe(1)-Fe(8) bond length is 2.64 Å. The Fe(1)-Fe(9) bond length is 2.63 Å. The Fe(1)-Si(1) bond length is 2.65 Å. The Fe(1)-Si(2) bond length is 2.58 Å. In the second Fe site, Fe(2) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(11), one Fe(4), one Fe(5), one Fe(6), one Fe(8), one Fe(9), two equivalent Fe(3), and one Si(2) atom. The Fe(2)-Fe(11) bond length is 2.46 Å. The Fe(2)-Fe(4) bond length is 2.54 Å. The Fe(2)-Fe(5) bond length is 2.51 Å. The Fe(2)-Fe(6) bond length is 2.65 Å. The Fe(2)-Fe(8) bond length is 2.48 Å. The Fe(2)-Fe(9) bond length is 2.63 Å. There is one shorter (2.49 Å) and one longer (2.51 Å) Fe(2)-Fe(3) bond length. The Fe(2)-Si(2) bond length is 2.41 Å. In the third Fe site, Fe(3) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(4), one Fe(5), one Fe(7), one Fe(8), one Fe(9), two equivalent Fe(2), one Si(1), and one Si(2) atom. The Fe(3)-Fe(4) bond length is 2.48 Å. The Fe(3)-Fe(5) bond length is 2.54 Å. The Fe(3)-Fe(7) bond length is 2.62 Å. The Fe(3)-Fe(8) bond length is 2.63 Å. The Fe(3)-Fe(9) bond length is 2.47 Å. The Fe(3)-Si(1) bond length is 2.42 Å. The Fe(3)-Si(2) bond length is 2.41 Å. In the fourth Fe site, Fe(4) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(10), one Fe(2), one Fe(3), one Fe(5), one Fe(6), one Fe(7), two equivalent Fe(8), and one Si(1) atom. The Fe(4)-Fe(10) bond length is 2.50 Å. The Fe(4)-Fe(5) bond length is 2.69 Å. The Fe(4)-Fe(6) bond length is 2.43 Å. The Fe(4)-Fe(7) bond length is 2.63 Å. There is one shorter (2.46 Å) and one longer (2.54 Å) Fe(4)-Fe(8) bond length. The Fe(4)-Si(1) bond length is 2.40 Å. In the fifth Fe site, Fe(5) is bonded to two equivalent Ce(1), one Fe(1), one Fe(10), one Fe(11), one Fe(2), one Fe(3), one Fe(4), one Fe(6), one Fe(7), and two equivalent Fe(9) atoms to form distorted FeCe2Fe10 cuboctahedra that share  a cornercorner with one Fe(10)Ce2Fe10 cuboctahedra, corners with two equivalent Fe(5)Ce2Fe10 cuboctahedra, corners with two equivalent C(1)Ce2Fe4 octahedra,  an edgeedge with one C(1)Ce2Fe4 octahedra,  a faceface with one Fe(10)Ce2Fe10 cuboctahedra, and  a faceface with one Fe(5)Ce2Fe10 cuboctahedra. The corner-sharing octahedral tilt angles range from 28-71°. The Fe(5)-Fe(10) bond length is 2.49 Å. The Fe(5)-Fe(11) bond length is 2.40 Å. The Fe(5)-Fe(6) bond length is 2.65 Å. The Fe(5)-Fe(7) bond length is 2.43 Å. There is one shorter (2.46 Å) and one longer (2.56 Å) Fe(5)-Fe(9) bond length. In the sixth Fe site, Fe(6) is bonded in a single-bond geometry to one Fe(1), one Fe(10), one Fe(11), one Fe(2), one Fe(4), one Fe(5), one Fe(8), one Fe(9), and one C(1) atom. The Fe(6)-Fe(10) bond length is 2.40 Å. The Fe(6)-Fe(11) bond length is 2.39 Å. The Fe(6)-Fe(8) bond length is 2.56 Å. The Fe(6)-Fe(9) bond length is 2.48 Å. The Fe(6)-C(1) bond length is 1.86 Å. In the seventh Fe site, Fe(7) is bonded in a single-bond geometry to one Fe(1), one Fe(10), one Fe(3), one Fe(4), one Fe(5), one Fe(8), one Fe(9), one Si(1), and one C(1) atom. The Fe(7)-Fe(10) bond length is 2.38 Å. The Fe(7)-Fe(8) bond length is 2.49 Å. The Fe(7)-Fe(9) bond length is 2.59 Å. The Fe(7)-Si(1) bond length is 2.38 Å. The Fe(7)-C(1) bond length is 1.87 Å. In the eighth Fe site, Fe(8) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(2), one Fe(3), one Fe(6), one Fe(7), one Fe(9), two equivalent Fe(4), one Si(1), and one Si(2) atom. The Fe(8)-Fe(9) bond length is 2.57 Å. The Fe(8)-Si(1) bond length is 2.39 Å. The Fe(8)-Si(2) bond length is 2.41 Å. In the ninth Fe site, Fe(9) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Fe(1), one Fe(11), one Fe(2), one Fe(3), one Fe(6), one Fe(7), one Fe(8), two equivalent Fe(5), and one Si(2) atom. The Fe(9)-Fe(11) bond length is 2.39 Å. The Fe(9)-Si(2) bond length is 2.39 Å. In the tenth Fe site, Fe(10) is bonded to two equivalent Ce(1), two equivalent Fe(1), two equivalent Fe(4), two equivalent Fe(5), two equivalent Fe(6), and two equivalent Fe(7) atoms to form distorted FeCe2Fe10 cuboctahedra that share corners with two equivalent Fe(5)Ce2Fe10 cuboctahedra, faces with two equivalent Fe(5)Ce2Fe10 cuboctahedra, and faces with two equivalent C(1)Ce2Fe4 octahedra. In the eleventh Fe site, Fe(11) is bonded in a 12-coordinate geometry to two equivalent Ce(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(5), two equivalent Fe(6), and two equivalent Fe(9) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to two equivalent Fe(1), two equivalent Fe(3), two equivalent Fe(4), two equivalent Fe(7), and two equivalent Fe(8) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), two equivalent Fe(8), and two equivalent Fe(9) atoms. C(1) is bonded to two equivalent Ce(1), two equivalent Fe(6), and two equivalent Fe(7) atoms to form CCe2Fe4 octahedra that share corners with four equivalent Fe(5)Ce2Fe10 cuboctahedra, edges with two equivalent Fe(5)Ce2Fe10 cuboctahedra, and faces with two equivalent Fe(10)Ce2Fe10 cuboctahedra.