Cs3Sb2I9 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) 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(2)I12 cuboctahedra, and faces with six equivalent Sb(1)I6 octahedra. In the second Cs site, Cs(2) is bonded to three equivalent I(1) and nine equivalent I(2) atoms to form CsI12 cuboctahedra that share corners with three equivalent Cs(1)I12 cuboctahedra, corners with nine equivalent Cs(2)I12 cuboctahedra, faces with three equivalent Cs(1)I12 cuboctahedra, faces with three equivalent Cs(2)I12 cuboctahedra, and faces with five equivalent Sb(1)I6 octahedra. Sb(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form SbI6 octahedra that share corners with three equivalent Sb(1)I6 octahedra, faces with three equivalent Cs(1)I12 cuboctahedra, and faces with five equivalent Cs(2)I12 cuboctahedra. The corner-sharing octahedra are not tilted. There are two inequivalent I sites. In the first I site, I(1) is bonded to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Sb(1) atoms to form ICs4Sb2 octahedra that share corners with six equivalent I(1)Cs4Sb2 octahedra, corners with sixteen equivalent I(2)Cs4Sb square pyramids, edges with four equivalent I(2)Cs4Sb square pyramids, faces with four equivalent I(1)Cs4Sb2 octahedra, and faces with four equivalent I(2)Cs4Sb square pyramids. The corner-sharing octahedral tilt angles range from 0-60°. In the second I site, I(2) is bonded to one Cs(1), three equivalent Cs(2), and one Sb(1) atom to form distorted ICs4Sb square pyramids that share corners with eight equivalent I(1)Cs4Sb2 octahedra, corners with thirteen equivalent I(2)Cs4Sb square pyramids, edges with two equivalent I(1)Cs4Sb2 octahedra, edges with six equivalent I(2)Cs4Sb square pyramids, faces with two equivalent I(1)Cs4Sb2 octahedra, and faces with two equivalent I(2)Cs4Sb square pyramids. The corner-sharing octahedral tilt angles range from 1-60°.
Cs3Sb2I9 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) 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(2)I12 cuboctahedra, and faces with six equivalent Sb(1)I6 octahedra. All Cs(1)-I(1) bond lengths are 4.26 Å. All Cs(1)-I(2) bond lengths are 4.32 Å. In the second Cs site, Cs(2) is bonded to three equivalent I(1) and nine equivalent I(2) atoms to form CsI12 cuboctahedra that share corners with three equivalent Cs(1)I12 cuboctahedra, corners with nine equivalent Cs(2)I12 cuboctahedra, faces with three equivalent Cs(1)I12 cuboctahedra, faces with three equivalent Cs(2)I12 cuboctahedra, and faces with five equivalent Sb(1)I6 octahedra. All Cs(2)-I(1) bond lengths are 4.25 Å. There are six shorter (4.26 Å) and three longer (4.29 Å) Cs(2)-I(2) bond lengths. Sb(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form SbI6 octahedra that share corners with three equivalent Sb(1)I6 octahedra, faces with three equivalent Cs(1)I12 cuboctahedra, and faces with five equivalent Cs(2)I12 cuboctahedra. The corner-sharing octahedra are not tilted. All Sb(1)-I(1) bond lengths are 3.16 Å. All Sb(1)-I(2) bond lengths are 2.90 Å. There are two inequivalent I sites. In the first I site, I(1) is bonded to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Sb(1) atoms to form ICs4Sb2 octahedra that share corners with six equivalent I(1)Cs4Sb2 octahedra, corners with sixteen equivalent I(2)Cs4Sb square pyramids, edges with four equivalent I(2)Cs4Sb square pyramids, faces with four equivalent I(1)Cs4Sb2 octahedra, and faces with four equivalent I(2)Cs4Sb square pyramids. The corner-sharing octahedral tilt angles range from 0-60°. In the second I site, I(2) is bonded to one Cs(1), three equivalent Cs(2), and one Sb(1) atom to form distorted ICs4Sb square pyramids that share corners with eight equivalent I(1)Cs4Sb2 octahedra, corners with thirteen equivalent I(2)Cs4Sb square pyramids, edges with two equivalent I(1)Cs4Sb2 octahedra, edges with six equivalent I(2)Cs4Sb square pyramids, faces with two equivalent I(1)Cs4Sb2 octahedra, and faces with two equivalent I(2)Cs4Sb square pyramids. The corner-sharing octahedral tilt angles range from 1-60°.