The crystal structure described by Cs3Er2I9 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a distorted q6 geometry to nine equivalent I(1) atoms. 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(2)I12 cuboctahedra and faces with six equivalent Er(1)I6 octahedra. Er(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form ErI6 octahedra that share faces with three equivalent Cs(2)I12 cuboctahedra and  a faceface with one Er(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 Er(1) atom. In the second I site, I(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Cs(2) and two equivalent Er(1) atoms. is represented by the CIF file [CIF]
data_Cs3Er2I9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.482
_cell_length_b   8.482
_cell_length_c   21.434
_cell_angle_alpha   90.019
_cell_angle_beta   89.987
_cell_angle_gamma   119.999
_symmetry_Int_Tables_number   1
_cell_volume   1335.467
_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  0.432  1.0
  Cs  Cs1  1  0.667  0.333  0.568  1.0
  Cs  Cs2  1  0.667  0.333  0.932  1.0
  Cs  Cs3  1  0.333  0.667  0.068  1.0
  Cs  Cs4  1  1.000  0.000  0.250  1.0
  Cs  Cs5  1  0.000  1.000  0.750  1.0
  Er  Er6  1  0.667  0.333  0.344  1.0
  Er  Er7  1  0.333  0.667  0.656  1.0
  Er  Er8  1  0.333  0.667  0.844  1.0
  Er  Er9  1  0.667  0.333  0.156  1.0
  I  I10  1  0.835  0.670  0.415  1.0
  I  I11  1  0.330  0.165  0.415  1.0
  I  I12  1  0.835  0.165  0.415  1.0
  I  I13  1  0.165  0.330  0.585  1.0
  I  I14  1  0.671  0.835  0.585  1.0
  I  I15  1  0.165  0.835  0.585  1.0
  I  I16  1  0.165  0.330  0.915  1.0
  I  I17  1  0.671  0.835  0.915  1.0
  I  I18  1  0.165  0.835  0.915  1.0
  I  I19  1  0.835  0.671  0.085  1.0
  I  I20  1  0.329  0.165  0.085  1.0
  I  I21  1  0.835  0.165  0.085  1.0
  I  I22  1  0.505  0.010  0.250  1.0
  I  I23  1  0.990  0.495  0.250  1.0
  I  I24  1  0.505  0.495  0.250  1.0
  I  I25  1  0.495  0.990  0.750  1.0
  I  I26  1  0.010  0.505  0.750  1.0
  I  I27  1  0.495  0.505  0.750  1.0
[/CIF]
.
The crystal structure described by Cs3Er2I9 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a distorted q6 geometry to nine equivalent I(1) atoms. 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(2)I12 cuboctahedra and faces with six equivalent Er(1)I6 octahedra. Er(1) is bonded to three equivalent I(1) and three equivalent I(2) atoms to form ErI6 octahedra that share faces with three equivalent Cs(2)I12 cuboctahedra and  a faceface with one Er(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 Er(1) atom. In the second I site, I(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Cs(2) and two equivalent Er(1) atoms. is represented by the CIF file [CIF]
data_Cs3Er2I9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.482
_cell_length_b   8.482
_cell_length_c   21.434
_cell_angle_alpha   90.019
_cell_angle_beta   89.987
_cell_angle_gamma   119.999
_symmetry_Int_Tables_number   1
_cell_volume   1335.467
_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  0.432  1.0
  Cs  Cs1  1  0.667  0.333  0.568  1.0
  Cs  Cs2  1  0.667  0.333  0.932  1.0
  Cs  Cs3  1  0.333  0.667  0.068  1.0
  Cs  Cs4  1  1.000  0.000  0.250  1.0
  Cs  Cs5  1  0.000  1.000  0.750  1.0
  Er  Er6  1  0.667  0.333  0.344  1.0
  Er  Er7  1  0.333  0.667  0.656  1.0
  Er  Er8  1  0.333  0.667  0.844  1.0
  Er  Er9  1  0.667  0.333  0.156  1.0
  I  I10  1  0.835  0.670  0.415  1.0
  I  I11  1  0.330  0.165  0.415  1.0
  I  I12  1  0.835  0.165  0.415  1.0
  I  I13  1  0.165  0.330  0.585  1.0
  I  I14  1  0.671  0.835  0.585  1.0
  I  I15  1  0.165  0.835  0.585  1.0
  I  I16  1  0.165  0.330  0.915  1.0
  I  I17  1  0.671  0.835  0.915  1.0
  I  I18  1  0.165  0.835  0.915  1.0
  I  I19  1  0.835  0.671  0.085  1.0
  I  I20  1  0.329  0.165  0.085  1.0
  I  I21  1  0.835  0.165  0.085  1.0
  I  I22  1  0.505  0.010  0.250  1.0
  I  I23  1  0.990  0.495  0.250  1.0
  I  I24  1  0.505  0.495  0.250  1.0
  I  I25  1  0.495  0.990  0.750  1.0
  I  I26  1  0.010  0.505  0.750  1.0
  I  I27  1  0.495  0.505  0.750  1.0
[/CIF]
.