The crystal structure described by Cs3Cr2I9 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 Cr(1)I6 octahedra, faces with three equivalent Cs(2)I12 cuboctahedra, faces with four equivalent Cs(1)I12 cuboctahedra, and faces with four equivalent Cr(1)I6 octahedra. The corner-sharing octahedral tilt angles are 16°. 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 Cr(1)I6 octahedra. Cr(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form CrI6 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 Cr(1)I6 octahedra. There are two inequivalent I sites. In the first I site, I(1) is bonded in a distorted single-bond geometry to one Cs(2), three equivalent Cs(1), and one Cr(1) atom. 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 Cr(1) atoms. is represented by the CIF file [CIF]
data_Cs3Cr2I9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.182
_cell_length_b   8.182
_cell_length_c   20.629
_cell_angle_alpha   89.997
_cell_angle_beta   90.008
_cell_angle_gamma   120.007
_symmetry_Int_Tables_number   1
_cell_volume   1195.961
_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  0.431  1.0
  Cs  Cs1  1  0.667  0.333  0.931  1.0
  Cs  Cs2  1  1.000  1.000  0.250  1.0
  Cs  Cs3  1  0.333  0.667  0.069  1.0
  Cs  Cs4  1  1.000  1.000  0.750  1.0
  Cs  Cs5  1  0.667  0.333  0.569  1.0
  Cr  Cr6  1  0.667  0.333  0.163  1.0
  Cr  Cr7  1  0.333  0.667  0.837  1.0
  Cr  Cr8  1  0.333  0.667  0.663  1.0
  Cr  Cr9  1  0.667  0.333  0.337  1.0
  I  I10  1  0.826  0.652  0.092  1.0
  I  I11  1  0.513  0.487  0.250  1.0
  I  I12  1  0.513  0.026  0.250  1.0
  I  I13  1  0.026  0.513  0.750  1.0
  I  I14  1  0.652  0.826  0.592  1.0
  I  I15  1  0.174  0.826  0.592  1.0
  I  I16  1  0.974  0.487  0.250  1.0
  I  I17  1  0.348  0.174  0.092  1.0
  I  I18  1  0.826  0.174  0.408  1.0
  I  I19  1  0.174  0.348  0.908  1.0
  I  I20  1  0.487  0.513  0.750  1.0
  I  I21  1  0.174  0.348  0.592  1.0
  I  I22  1  0.487  0.974  0.750  1.0
  I  I23  1  0.348  0.174  0.408  1.0
  I  I24  1  0.826  0.174  0.092  1.0
  I  I25  1  0.826  0.652  0.408  1.0
  I  I26  1  0.174  0.826  0.908  1.0
  I  I27  1  0.652  0.826  0.908  1.0
[/CIF]
.
The crystal structure described by Cs3Cr2I9 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 Cr(1)I6 octahedra, faces with three equivalent Cs(2)I12 cuboctahedra, faces with four equivalent Cs(1)I12 cuboctahedra, and faces with four equivalent Cr(1)I6 octahedra. The corner-sharing octahedral tilt angles are 16°. 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 Cr(1)I6 octahedra. Cr(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form CrI6 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 Cr(1)I6 octahedra. There are two inequivalent I sites. In the first I site, I(1) is bonded in a distorted single-bond geometry to one Cs(2), three equivalent Cs(1), and one Cr(1) atom. 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 Cr(1) atoms. is represented by the CIF file [CIF]
data_Cs3Cr2I9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.182
_cell_length_b   8.182
_cell_length_c   20.629
_cell_angle_alpha   89.997
_cell_angle_beta   90.008
_cell_angle_gamma   120.007
_symmetry_Int_Tables_number   1
_cell_volume   1195.961
_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  0.431  1.0
  Cs  Cs1  1  0.667  0.333  0.931  1.0
  Cs  Cs2  1  1.000  1.000  0.250  1.0
  Cs  Cs3  1  0.333  0.667  0.069  1.0
  Cs  Cs4  1  1.000  1.000  0.750  1.0
  Cs  Cs5  1  0.667  0.333  0.569  1.0
  Cr  Cr6  1  0.667  0.333  0.163  1.0
  Cr  Cr7  1  0.333  0.667  0.837  1.0
  Cr  Cr8  1  0.333  0.667  0.663  1.0
  Cr  Cr9  1  0.667  0.333  0.337  1.0
  I  I10  1  0.826  0.652  0.092  1.0
  I  I11  1  0.513  0.487  0.250  1.0
  I  I12  1  0.513  0.026  0.250  1.0
  I  I13  1  0.026  0.513  0.750  1.0
  I  I14  1  0.652  0.826  0.592  1.0
  I  I15  1  0.174  0.826  0.592  1.0
  I  I16  1  0.974  0.487  0.250  1.0
  I  I17  1  0.348  0.174  0.092  1.0
  I  I18  1  0.826  0.174  0.408  1.0
  I  I19  1  0.174  0.348  0.908  1.0
  I  I20  1  0.487  0.513  0.750  1.0
  I  I21  1  0.174  0.348  0.592  1.0
  I  I22  1  0.487  0.974  0.750  1.0
  I  I23  1  0.348  0.174  0.408  1.0
  I  I24  1  0.826  0.174  0.092  1.0
  I  I25  1  0.826  0.652  0.408  1.0
  I  I26  1  0.174  0.826  0.908  1.0
  I  I27  1  0.652  0.826  0.908  1.0
[/CIF]
.