Cs3Mo2I9 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to three equivalent I(2) and nine equivalent I(1) atoms to form distorted CsI12 cuboctahedra that share corners with three equivalent Cs(2)I12 cuboctahedra, corners with six equivalent Cs(1)I12 cuboctahedra, corners with three equivalent Mo(1)I6 octahedra, faces with three equivalent Cs(2)I12 cuboctahedra, faces with four equivalent Cs(1)I12 cuboctahedra, and faces with four equivalent Mo(1)I6 octahedra. The corner-sharing octahedral tilt angles are 24°. In the second Cs site, Cs(2) is bonded to six equivalent I(1) and six equivalent I(2) atoms to form CsI12 cuboctahedra that share corners with six equivalent Cs(1)I12 cuboctahedra, corners with six equivalent Cs(2)I12 cuboctahedra, faces with six equivalent Cs(1)I12 cuboctahedra, and faces with six equivalent Mo(1)I6 octahedra. Mo(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form MoI6 octahedra that share corners with three equivalent Cs(1)I12 cuboctahedra, faces with three equivalent Cs(2)I12 cuboctahedra, faces with four equivalent Cs(1)I12 cuboctahedra, and  a faceface with one Mo(1)I6 octahedra. There are two inequivalent I sites. In the first I site, I(1) is bonded to one Cs(2), three equivalent Cs(1), and one Mo(1) atom to form a mixture of distorted corner, edge, and face-sharing ICs4Mo square pyramids. In the second I site, I(2) is bonded in a 2-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Mo(1) atoms.
Cs3Mo2I9 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to three equivalent I(2) and nine equivalent I(1) atoms to form distorted CsI12 cuboctahedra that share corners with three equivalent Cs(2)I12 cuboctahedra, corners with six equivalent Cs(1)I12 cuboctahedra, corners with three equivalent Mo(1)I6 octahedra, faces with three equivalent Cs(2)I12 cuboctahedra, faces with four equivalent Cs(1)I12 cuboctahedra, and faces with four equivalent Mo(1)I6 octahedra. The corner-sharing octahedral tilt angles are 24°. All Cs(1)-I(2) bond lengths are 4.53 Å. There are three shorter (4.01 Å) and six longer (4.27 Å) Cs(1)-I(1) bond lengths. In the second Cs site, Cs(2) is bonded to six equivalent I(1) and six equivalent I(2) atoms to form CsI12 cuboctahedra that share corners with six equivalent Cs(1)I12 cuboctahedra, corners with six equivalent Cs(2)I12 cuboctahedra, faces with six equivalent Cs(1)I12 cuboctahedra, and faces with six equivalent Mo(1)I6 octahedra. All Cs(2)-I(1) bond lengths are 4.09 Å. All Cs(2)-I(2) bond lengths are 4.22 Å. Mo(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form MoI6 octahedra that share corners with three equivalent Cs(1)I12 cuboctahedra, faces with three equivalent Cs(2)I12 cuboctahedra, faces with four equivalent Cs(1)I12 cuboctahedra, and  a faceface with one Mo(1)I6 octahedra. All Mo(1)-I(1) bond lengths are 2.82 Å. All Mo(1)-I(2) bond lengths are 2.80 Å. There are two inequivalent I sites. In the first I site, I(1) is bonded to one Cs(2), three equivalent Cs(1), and one Mo(1) atom to form a mixture of distorted corner, edge, and face-sharing ICs4Mo square pyramids. In the second I site, I(2) is bonded in a 2-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Mo(1) atoms.