DOE OSTI2020
FeTlBr3 crystallizes in the hexagonal P6_3cm space group. The structure is three-dimensional. there are two inequivalent Fe2+ sites. In the first Fe2+ site, Fe2+ is bonded to six equivalent Br1- atoms to form FeBr6 octahedra that share corners with six equivalent TlBr12 cuboctahedra, faces with six equivalent TlBr12 cuboctahedra, and faces with two equivalent FeBr6 octahedra. There are three shorter (2.45 Å) and three longer (2.46 Å) Fe–Br bond lengths. In the second Fe2+ site, Fe2+ is bonded to six equivalent Br1- atoms to form FeBr6 octahedra that share corners with six equivalent TlBr12 cuboctahedra, faces with six equivalent TlBr12 cuboctahedra, and faces with two equivalent FeBr6 octahedra. There are three shorter (2.63 Å) and three longer (2.66 Å) Fe–Br bond lengths. Tl1+ is bonded to twelve Br1- atoms to form distorted TlBr12 cuboctahedra that share corners with six equivalent TlBr12 cuboctahedra, corners with six FeBr6 octahedra, faces with eight equivalent TlBr12 cuboctahedra, and faces with six FeBr6 octahedra. The corner-sharing octahedra tilt angles range from 13–25°. There are a spread of Tl–Br bond distances ranging from 3.33–3.92 Å. There are two inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 6-coordinate geometry to two equivalent Fe2+ and four equivalent Tl1+ atoms. In the second Br1- site, Br1- is bonded in a 2-coordinate geometry to two equivalent Fe2+ and four equivalent Tl1+ atoms.