Dy2Fe15Si2C crystallizes in the monoclinic C2/m space group. Dy(1) is bonded in a distorted single-bond geometry to one Fe(3), two equivalent Fe(4), four equivalent Fe(6), six equivalent Fe(2), one Si(1), and one C(1) atom. There are six 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(6), one Si(1), and one C(1) atom. In the second Fe site, Fe(2) is bonded to three equivalent Dy(1), one Fe(1), one Fe(2), one Fe(3), one Fe(4), one Fe(5), three equivalent Fe(6), and one Si(1) atom to form FeDy3Fe8Si cuboctahedra that share  a cornercorner with one Fe(3)Dy2Fe8Si2 cuboctahedra, corners with four equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, corners with seven equivalent Fe(2)Dy3Fe8Si cuboctahedra, corners with two equivalent C(1)Dy2Fe4 octahedra,  an edgeedge with one Fe(3)Dy2Fe8Si2 cuboctahedra, edges with two equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, edges with three equivalent Fe(2)Dy3Fe8Si cuboctahedra,  a faceface with one Fe(3)Dy2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, faces with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, and  a faceface with one C(1)Dy2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 65-71°. In the third Fe site, Fe(3) is bonded to two equivalent Dy(1), four equivalent Fe(2), four equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeDy2Fe8Si2 cuboctahedra that share corners with four equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, corners with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, corners with two equivalent C(1)Dy2Fe4 octahedra, edges with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, faces with four equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, and faces with four equivalent Fe(2)Dy3Fe8Si cuboctahedra. The corner-sharing octahedral tilt angles are 47°. 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(5), two equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeDy2Fe8Si2 cuboctahedra that share corners with two equivalent Fe(3)Dy2Fe8Si2 cuboctahedra, corners with two equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, corners with eight equivalent Fe(2)Dy3Fe8Si cuboctahedra, edges with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, faces with two equivalent Fe(3)Dy2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, faces with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, and faces with two equivalent C(1)Dy2Fe4 octahedra. In the fifth Fe site, Fe(5) is bonded in a single-bond geometry to two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(6), two equivalent Si(1), and one C(1) atom. In the sixth Fe site, Fe(6) is bonded in a 12-coordinate geometry to two equivalent Dy(1), one Fe(1), one Fe(3), one Fe(4), one Fe(5), one Fe(6), three equivalent Fe(2), and two equivalent Si(1) atoms. Si(1) is bonded in a 14-coordinate geometry to one Dy(1), one Fe(1), one Fe(3), two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(5), four equivalent Fe(6), and one Si(1) atom. C(1) is bonded to two equivalent Dy(1), two equivalent Fe(1), and two equivalent Fe(5) atoms to form CDy2Fe4 octahedra that share corners with two equivalent Fe(3)Dy2Fe8Si2 cuboctahedra, corners with eight equivalent Fe(2)Dy3Fe8Si cuboctahedra, faces with four equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, and faces with four equivalent Fe(2)Dy3Fe8Si cuboctahedra.
Dy2Fe15Si2C crystallizes in the monoclinic C2/m space group. Dy(1) is bonded in a distorted single-bond geometry to one Fe(3), two equivalent Fe(4), four equivalent Fe(6), six equivalent Fe(2), one Si(1), and one C(1) atom. The Dy(1)-Fe(3) bond length is 3.30 Å. Both Dy(1)-Fe(4) bond lengths are 3.33 Å. There are two shorter (2.91 Å) and two longer (2.97 Å) Dy(1)-Fe(6) bond lengths. There are a spread of Dy(1)-Fe(2) bond distances ranging from 3.05-3.22 Å. The Dy(1)-Si(1) bond length is 3.07 Å. The Dy(1)-C(1) bond length is 2.48 Å. There are six 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(6), one Si(1), and one C(1) atom. Both Fe(1)-Fe(2) bond lengths are 2.49 Å. Both Fe(1)-Fe(4) bond lengths are 2.43 Å. Both Fe(1)-Fe(6) bond lengths are 2.59 Å. The Fe(1)-Si(1) bond length is 2.60 Å. The Fe(1)-C(1) bond length is 1.92 Å. In the second Fe site, Fe(2) is bonded to three equivalent Dy(1), one Fe(1), one Fe(2), one Fe(3), one Fe(4), one Fe(5), three equivalent Fe(6), and one Si(1) atom to form FeDy3Fe8Si cuboctahedra that share  a cornercorner with one Fe(3)Dy2Fe8Si2 cuboctahedra, corners with four equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, corners with seven equivalent Fe(2)Dy3Fe8Si cuboctahedra, corners with two equivalent C(1)Dy2Fe4 octahedra,  an edgeedge with one Fe(3)Dy2Fe8Si2 cuboctahedra, edges with two equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, edges with three equivalent Fe(2)Dy3Fe8Si cuboctahedra,  a faceface with one Fe(3)Dy2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, faces with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, and  a faceface with one C(1)Dy2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 65-71°. The Fe(2)-Fe(2) bond length is 2.46 Å. The Fe(2)-Fe(3) bond length is 2.40 Å. The Fe(2)-Fe(4) bond length is 2.43 Å. The Fe(2)-Fe(5) bond length is 2.52 Å. There are a spread of Fe(2)-Fe(6) bond distances ranging from 2.56-2.60 Å. The Fe(2)-Si(1) bond length is 2.57 Å. In the third Fe site, Fe(3) is bonded to two equivalent Dy(1), four equivalent Fe(2), four equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeDy2Fe8Si2 cuboctahedra that share corners with four equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, corners with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, corners with two equivalent C(1)Dy2Fe4 octahedra, edges with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, faces with four equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, and faces with four equivalent Fe(2)Dy3Fe8Si cuboctahedra. The corner-sharing octahedral tilt angles are 47°. All Fe(3)-Fe(6) bond lengths are 2.46 Å. Both Fe(3)-Si(1) bond lengths are 2.58 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(5), two equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeDy2Fe8Si2 cuboctahedra that share corners with two equivalent Fe(3)Dy2Fe8Si2 cuboctahedra, corners with two equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, corners with eight equivalent Fe(2)Dy3Fe8Si cuboctahedra, edges with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, faces with two equivalent Fe(3)Dy2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, faces with four equivalent Fe(2)Dy3Fe8Si cuboctahedra, and faces with two equivalent C(1)Dy2Fe4 octahedra. Both Fe(4)-Fe(5) bond lengths are 2.44 Å. Both Fe(4)-Fe(6) bond lengths are 2.45 Å. Both Fe(4)-Si(1) bond lengths are 2.56 Å. In the fifth Fe site, Fe(5) is bonded in a single-bond geometry to two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(6), two equivalent Si(1), and one C(1) atom. Both Fe(5)-Fe(6) bond lengths are 2.47 Å. Both Fe(5)-Si(1) bond lengths are 2.69 Å. The Fe(5)-C(1) bond length is 1.85 Å. In the sixth Fe site, Fe(6) is bonded in a 12-coordinate geometry to two equivalent Dy(1), one Fe(1), one Fe(3), one Fe(4), one Fe(5), one Fe(6), three equivalent Fe(2), and two equivalent Si(1) atoms. The Fe(6)-Fe(6) bond length is 2.52 Å. There is one shorter (2.83 Å) and one longer (2.87 Å) Fe(6)-Si(1) bond length. Si(1) is bonded in a 14-coordinate geometry to one Dy(1), one Fe(1), one Fe(3), two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(5), four equivalent Fe(6), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.55 Å. C(1) is bonded to two equivalent Dy(1), two equivalent Fe(1), and two equivalent Fe(5) atoms to form CDy2Fe4 octahedra that share corners with two equivalent Fe(3)Dy2Fe8Si2 cuboctahedra, corners with eight equivalent Fe(2)Dy3Fe8Si cuboctahedra, faces with four equivalent Fe(4)Dy2Fe8Si2 cuboctahedra, and faces with four equivalent Fe(2)Dy3Fe8Si cuboctahedra.