Cs3AlI6 crystallizes in the cubic Fm-3m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to twelve equivalent I(1) atoms to form distorted CsI12 cuboctahedra that share corners with twelve equivalent Cs(1)I12 cuboctahedra, faces with six equivalent Cs(1)I12 cuboctahedra, faces with four equivalent Cs(2)I6 octahedra, and faces with four equivalent Al(1)I6 octahedra. In the second Cs site, Cs(2) is bonded to six equivalent I(1) atoms to form CsI6 octahedra that share corners with six equivalent Al(1)I6 octahedra and faces with eight equivalent Cs(1)I12 cuboctahedra. The corner-sharing octahedra are not tilted. Al(1) is bonded to six equivalent I(1) atoms to form AlI6 octahedra that share corners with six equivalent Cs(2)I6 octahedra and faces with eight equivalent Cs(1)I12 cuboctahedra. The corner-sharing octahedra are not tilted. I(1) is bonded in a distorted linear geometry to one Cs(2), four equivalent Cs(1), and one Al(1) atom.
Cs3AlI6 crystallizes in the cubic Fm-3m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to twelve equivalent I(1) atoms to form distorted CsI12 cuboctahedra that share corners with twelve equivalent Cs(1)I12 cuboctahedra, faces with six equivalent Cs(1)I12 cuboctahedra, faces with four equivalent Cs(2)I6 octahedra, and faces with four equivalent Al(1)I6 octahedra. All Cs(1)-I(1) bond lengths are 4.54 Å. In the second Cs site, Cs(2) is bonded to six equivalent I(1) atoms to form CsI6 octahedra that share corners with six equivalent Al(1)I6 octahedra and faces with eight equivalent Cs(1)I12 cuboctahedra. The corner-sharing octahedra are not tilted. All Cs(2)-I(1) bond lengths are 3.62 Å. Al(1) is bonded to six equivalent I(1) atoms to form AlI6 octahedra that share corners with six equivalent Cs(2)I6 octahedra and faces with eight equivalent Cs(1)I12 cuboctahedra. The corner-sharing octahedra are not tilted. All Al(1)-I(1) bond lengths are 2.78 Å. I(1) is bonded in a distorted linear geometry to one Cs(2), four equivalent Cs(1), and one Al(1) atom.