DOE OSTI2020
Sm2Fe15Si2C crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Sm is bonded in a distorted single-bond geometry to thirteen Fe, one Si, and one C atom. There are a spread of Sm–Fe bond distances ranging from 2.99–3.37 Å. The Sm–Si bond length is 3.08 Å. The Sm–C bond length is 2.55 Å. There are six inequivalent Fe sites. In the first Fe site, Fe is bonded in a single-bond geometry to six Fe, one Si, and one C atom. There are a spread of Fe–Fe bond distances ranging from 2.45–2.60 Å. The Fe–Si bond length is 2.62 Å. The Fe–C bond length is 1.93 Å. In the second Fe site, Fe is bonded to three equivalent Sm, eight Fe, and one Si atom to form FeSm3Fe8Si cuboctahedra that share corners with seventeen FeSm3Fe8Si cuboctahedra, corners with two equivalent CSm2Fe4 octahedra, edges with seven FeSm3Fe8Si cuboctahedra, faces with fourteen FeSm3Fe8Si cuboctahedra, and a faceface with one CSm2Fe4 octahedra. The corner-sharing octahedra tilt angles range from 65–72°. There are a spread of Fe–Fe bond distances ranging from 2.43–2.69 Å. The Fe–Si bond length is 2.60 Å. In the third Fe site, Fe is bonded in a single-bond geometry to six Fe, two equivalent Si, and one C atom. There are two shorter (2.44 Å) and two longer (2.45 Å) Fe–Fe bond lengths. Both Fe–Si bond lengths are 2.72 Å. The Fe–C bond length is 1.85 Å. In the fourth Fe site, Fe is bonded to two equivalent Sm, eight Fe, and two equivalent Si atoms to form distorted FeSm2Fe8Si2 cuboctahedra that share corners with sixteen FeSm3Fe8Si cuboctahedra, corners with two equivalent CSm2Fe4 octahedra, edges with four FeSm3Fe8Si cuboctahedra, an edgeedge with one CSm2Fe4 octahedra, and faces with fifteen FeSm3Fe8Si cuboctahedra. The corner-sharing octahedra tilt angles range from 25–29°. There are one shorter (2.45 Å) and two longer (2.46 Å) Fe–Fe bond lengths. There are one shorter (2.77 Å) and one longer (2.78 Å) Fe–Si bond lengths. In the fifth Fe site, Fe is bonded to two equivalent Sm, eight Fe, and two equivalent Si atoms to form distorted FeSm2Fe8Si2 cuboctahedra that share corners with twelve FeSm3Fe8Si cuboctahedra, corners with two equivalent CSm2Fe4 octahedra, edges with eight FeSm2Fe8Si2 cuboctahedra, and faces with twelve FeSm3Fe8Si cuboctahedra. The corner-sharing octahedral tilt angles are 47°. Both Fe–Si bond lengths are 2.60 Å. In the sixth Fe site, Fe is bonded to two equivalent Sm, eight Fe, and two equivalent Si atoms to form distorted FeSm2Fe8Si2 cuboctahedra that share corners with eighteen FeSm3Fe8Si cuboctahedra, edges with six FeSm2Fe8Si2 cuboctahedra, faces with fourteen FeSm3Fe8Si cuboctahedra, and faces with two equivalent CSm2Fe4 octahedra. Both Fe–Si bond lengths are 2.59 Å. Si is bonded in a 7-coordinate geometry to one Sm, twelve Fe, and one Si atom. The Si–Si bond length is 2.55 Å. C is bonded to two equivalent Sm and four Fe atoms to form CSm2Fe4 octahedra that share corners with eighteen FeSm2Fe8Si2 cuboctahedra, edges with four equivalent FeSm2Fe8Si2 cuboctahedra, and faces with eight FeSm2Fe8Si2 cuboctahedra.