The crystal structure described by Cs3Bi2I9 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 CsI12 cuboctahedra that share corners with three equivalent Cs(2)I12 cuboctahedra, corners with six equivalent Cs(1)I12 cuboctahedra, corners with three equivalent Bi(1)I6 octahedra, faces with three equivalent Cs(2)I12 cuboctahedra, faces with four equivalent Cs(1)I12 cuboctahedra, and faces with four equivalent Bi(1)I6 octahedra. The corner-sharing octahedral tilt angles are 19°. 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 Bi(1)I6 octahedra. Bi(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form BiI6 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 Bi(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 Bi(1) atom to form distorted ICs4Bi square pyramids that share corners with eight equivalent I(2)Cs4Bi2 octahedra, corners with thirteen equivalent I(1)Cs4Bi square pyramids, edges with two equivalent I(2)Cs4Bi2 octahedra, edges with six equivalent I(1)Cs4Bi square pyramids, faces with two equivalent I(2)Cs4Bi2 octahedra, and faces with two equivalent I(1)Cs4Bi square pyramids. The corner-sharing octahedral tilt angles range from 4-64°. In the second I site, I(2) is bonded to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Bi(1) atoms to form distorted ICs4Bi2 octahedra that share corners with six equivalent I(2)Cs4Bi2 octahedra, corners with sixteen equivalent I(1)Cs4Bi square pyramids, edges with four equivalent I(1)Cs4Bi square pyramids, faces with four equivalent I(2)Cs4Bi2 octahedra, and faces with four equivalent I(1)Cs4Bi square pyramids. The corner-sharing octahedral tilt angles range from 1-60°. is represented by the CIF file [CIF]
data_Cs3Bi2I9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.540
_cell_length_b   8.539
_cell_length_c   21.632
_cell_angle_alpha   90.002
_cell_angle_beta   90.009
_cell_angle_gamma   119.995
_symmetry_Int_Tables_number   1
_cell_volume   1366.149
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Cs  Cs0  1  0.333  0.667  0.425  1.0
  Cs  Cs1  1  0.667  0.333  0.575  1.0
  Cs  Cs2  1  0.333  0.667  0.075  1.0
  Cs  Cs3  1  0.000  0.000  0.250  1.0
  Cs  Cs4  1  0.667  0.333  0.925  1.0
  Cs  Cs5  1  0.000  0.000  0.750  1.0
  Bi  Bi6  1  0.333  0.667  0.844  1.0
  Bi  Bi7  1  0.667  0.333  0.156  1.0
  Bi  Bi8  1  0.333  0.667  0.656  1.0
  Bi  Bi9  1  0.667  0.333  0.344  1.0
  I  I10  1  0.164  0.836  0.582  1.0
  I  I11  1  0.836  0.671  0.082  1.0
  I  I12  1  0.836  0.165  0.418  1.0
  I  I13  1  0.496  0.993  0.250  1.0
  I  I14  1  0.835  0.164  0.082  1.0
  I  I15  1  0.164  0.329  0.918  1.0
  I  I16  1  0.007  0.503  0.250  1.0
  I  I17  1  0.993  0.497  0.750  1.0
  I  I18  1  0.671  0.835  0.582  1.0
  I  I19  1  0.497  0.504  0.250  1.0
  I  I20  1  0.671  0.836  0.918  1.0
  I  I21  1  0.836  0.671  0.418  1.0
  I  I22  1  0.164  0.329  0.582  1.0
  I  I23  1  0.503  0.007  0.750  1.0
  I  I24  1  0.329  0.165  0.418  1.0
  I  I25  1  0.329  0.165  0.082  1.0
  I  I26  1  0.503  0.497  0.750  1.0
  I  I27  1  0.164  0.835  0.918  1.0
[/CIF]
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The crystal structure described by Cs3Bi2I9 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 CsI12 cuboctahedra that share corners with three equivalent Cs(2)I12 cuboctahedra, corners with six equivalent Cs(1)I12 cuboctahedra, corners with three equivalent Bi(1)I6 octahedra, faces with three equivalent Cs(2)I12 cuboctahedra, faces with four equivalent Cs(1)I12 cuboctahedra, and faces with four equivalent Bi(1)I6 octahedra. The corner-sharing octahedral tilt angles are 19°. 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 Bi(1)I6 octahedra. Bi(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form BiI6 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 Bi(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 Bi(1) atom to form distorted ICs4Bi square pyramids that share corners with eight equivalent I(2)Cs4Bi2 octahedra, corners with thirteen equivalent I(1)Cs4Bi square pyramids, edges with two equivalent I(2)Cs4Bi2 octahedra, edges with six equivalent I(1)Cs4Bi square pyramids, faces with two equivalent I(2)Cs4Bi2 octahedra, and faces with two equivalent I(1)Cs4Bi square pyramids. The corner-sharing octahedral tilt angles range from 4-64°. In the second I site, I(2) is bonded to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Bi(1) atoms to form distorted ICs4Bi2 octahedra that share corners with six equivalent I(2)Cs4Bi2 octahedra, corners with sixteen equivalent I(1)Cs4Bi square pyramids, edges with four equivalent I(1)Cs4Bi square pyramids, faces with four equivalent I(2)Cs4Bi2 octahedra, and faces with four equivalent I(1)Cs4Bi square pyramids. The corner-sharing octahedral tilt angles range from 1-60°. is represented by the CIF file [CIF]
data_Cs3Bi2I9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.540
_cell_length_b   8.539
_cell_length_c   21.632
_cell_angle_alpha   90.002
_cell_angle_beta   90.009
_cell_angle_gamma   119.995
_symmetry_Int_Tables_number   1
_cell_volume   1366.149
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Cs  Cs0  1  0.333  0.667  0.425  1.0
  Cs  Cs1  1  0.667  0.333  0.575  1.0
  Cs  Cs2  1  0.333  0.667  0.075  1.0
  Cs  Cs3  1  0.000  0.000  0.250  1.0
  Cs  Cs4  1  0.667  0.333  0.925  1.0
  Cs  Cs5  1  0.000  0.000  0.750  1.0
  Bi  Bi6  1  0.333  0.667  0.844  1.0
  Bi  Bi7  1  0.667  0.333  0.156  1.0
  Bi  Bi8  1  0.333  0.667  0.656  1.0
  Bi  Bi9  1  0.667  0.333  0.344  1.0
  I  I10  1  0.164  0.836  0.582  1.0
  I  I11  1  0.836  0.671  0.082  1.0
  I  I12  1  0.836  0.165  0.418  1.0
  I  I13  1  0.496  0.993  0.250  1.0
  I  I14  1  0.835  0.164  0.082  1.0
  I  I15  1  0.164  0.329  0.918  1.0
  I  I16  1  0.007  0.503  0.250  1.0
  I  I17  1  0.993  0.497  0.750  1.0
  I  I18  1  0.671  0.835  0.582  1.0
  I  I19  1  0.497  0.504  0.250  1.0
  I  I20  1  0.671  0.836  0.918  1.0
  I  I21  1  0.836  0.671  0.418  1.0
  I  I22  1  0.164  0.329  0.582  1.0
  I  I23  1  0.503  0.007  0.750  1.0
  I  I24  1  0.329  0.165  0.418  1.0
  I  I25  1  0.329  0.165  0.082  1.0
  I  I26  1  0.503  0.497  0.750  1.0
  I  I27  1  0.164  0.835  0.918  1.0
[/CIF]
.