Cs3Ho2Br9 crystallizes in the trigonal R-3c space group. Cs(1) is bonded to four equivalent Br(1) and eight equivalent Br(2) atoms to form CsBr12 cuboctahedra that share corners with six equivalent Cs(1)Br12 cuboctahedra, corners with four equivalent Ho(1)Br6 octahedra, faces with eight equivalent Cs(1)Br12 cuboctahedra, and faces with four equivalent Ho(1)Br6 octahedra. The corner-sharing octahedral tilt angles range from 12-30°. Ho(1) is bonded to three equivalent Br(1) and three equivalent Br(2) atoms to form HoBr6 octahedra that share corners with six equivalent Cs(1)Br12 cuboctahedra, faces with six equivalent Cs(1)Br12 cuboctahedra, and  a faceface with one Ho(1)Br6 octahedra. There are two inequivalent Br sites. In the first Br site, Br(2) is bonded in a distorted single-bond geometry to four equivalent Cs(1) and one Ho(1) atom. In the second Br site, Br(1) is bonded in a distorted L-shaped geometry to four equivalent Cs(1) and two equivalent Ho(1) atoms.
Cs3Ho2Br9 crystallizes in the trigonal R-3c space group. Cs(1) is bonded to four equivalent Br(1) and eight equivalent Br(2) atoms to form CsBr12 cuboctahedra that share corners with six equivalent Cs(1)Br12 cuboctahedra, corners with four equivalent Ho(1)Br6 octahedra, faces with eight equivalent Cs(1)Br12 cuboctahedra, and faces with four equivalent Ho(1)Br6 octahedra. The corner-sharing octahedral tilt angles range from 12-30°. There are two shorter (4.01 Å) and two longer (4.04 Å) Cs(1)-Br(1) bond lengths. There are a spread of Cs(1)-Br(2) bond distances ranging from 3.88-3.99 Å. Ho(1) is bonded to three equivalent Br(1) and three equivalent Br(2) atoms to form HoBr6 octahedra that share corners with six equivalent Cs(1)Br12 cuboctahedra, faces with six equivalent Cs(1)Br12 cuboctahedra, and  a faceface with one Ho(1)Br6 octahedra. All Ho(1)-Br(1) bond lengths are 2.88 Å. All Ho(1)-Br(2) bond lengths are 2.69 Å. There are two inequivalent Br sites. In the first Br site, Br(2) is bonded in a distorted single-bond geometry to four equivalent Cs(1) and one Ho(1) atom. In the second Br site, Br(1) is bonded in a distorted L-shaped geometry to four equivalent Cs(1) and two equivalent Ho(1) atoms.