DOE OSTI2020
Cr(Fe2Sb5)2 crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. Cr6+ is bonded to six Sb+1.80- atoms to form CrSb6 octahedra that share corners with eight FeSb6 octahedra and edges with two equivalent CrSb6 octahedra. The corner-sharing octahedra tilt angles range from 50–52°. There are one shorter (2.67 Å) and five longer (2.68 Å) Cr–Sb bond lengths. There are five inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six Sb+1.80- atoms to form a mixture of corner and edge-sharing FeSb6 octahedra. The corner-sharing octahedra tilt angles range from 50–51°. There are a spread of Fe–Sb bond distances ranging from 2.58–2.61 Å. In the second Fe3+ site, Fe3+ is bonded to six Sb+1.80- atoms to form a mixture of corner and edge-sharing FeSb6 octahedra. The corner-sharing octahedral tilt angles are 50°. There are two shorter (2.59 Å) and four longer (2.61 Å) Fe–Sb bond lengths. In the third Fe3+ site, Fe3+ is bonded to six Sb+1.80- atoms to form FeSb6 octahedra that share corners with four equivalent CrSb6 octahedra, corners with four equivalent FeSb6 octahedra, and edges with two equivalent FeSb6 octahedra. The corner-sharing octahedra tilt angles range from 50–51°. There are a spread of Fe–Sb bond distances ranging from 2.55–2.60 Å. In the fourth Fe3+ site, Fe3+ is bonded to six Sb+1.80- atoms to form FeSb6 octahedra that share corners with eight equivalent CrSb6 octahedra and edges with two equivalent FeSb6 octahedra. The corner-sharing octahedra tilt angles range from 50–52°. There are two shorter (2.52 Å) and four longer (2.57 Å) Fe–Sb bond lengths. In the fifth Fe3+ site, Fe3+ is bonded to six Sb+1.80- atoms to form a mixture of corner and edge-sharing FeSb6 octahedra. The corner-sharing octahedra tilt angles range from 50–51°. There are a spread of Fe–Sb bond distances ranging from 2.59–2.61 Å. There are ten inequivalent Sb+1.80- sites. In the first Sb+1.80- site, Sb+1.80- is bonded in a 3-coordinate geometry to one Cr6+ and two equivalent Fe3+ atoms. In the second Sb+1.80- site, Sb+1.80- is bonded in a 3-coordinate geometry to one Cr6+ and two equivalent Fe3+ atoms. In the third Sb+1.80- site, Sb+1.80- is bonded in a 4-coordinate geometry to three Fe3+ atoms. In the fourth Sb+1.80- site, Sb+1.80- is bonded in a 6-coordinate geometry to three Fe3+ atoms. In the fifth Sb+1.80- site, Sb+1.80- is bonded in a 6-coordinate geometry to three Fe3+ atoms. In the sixth Sb+1.80- site, Sb+1.80- is bonded in a 3-coordinate geometry to two equivalent Cr6+ and one Fe3+ atom. In the seventh Sb+1.80- site, Sb+1.80- is bonded in a 3-coordinate geometry to two equivalent Cr6+ and one Fe3+ atom. In the eighth Sb+1.80- site, Sb+1.80- is bonded in a 3-coordinate geometry to three Fe3+ atoms. In the ninth Sb+1.80- site, Sb+1.80- is bonded in a 6-coordinate geometry to three Fe3+ atoms. In the tenth Sb+1.80- site, Sb+1.80- is bonded in a 6-coordinate geometry to three Fe3+ atoms.