The compound described by CsEr3Se5 crystallizes in the orthorhombic Pnma space group. Cs(1) is bonded in a 7-coordinate geometry to one Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(5) atoms. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one Se(2), one Se(5), two equivalent Se(3), and two equivalent Se(4) atoms to form a mixture of edge and corner-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles are 2°. In the second Er site, Er(2) is bonded to one Se(1), one Se(3), two equivalent Se(4), and two equivalent Se(5) atoms to form a mixture of edge and corner-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 2-12°. In the third Er site, Er(3) is bonded to one Se(4), two equivalent Se(2), and three equivalent Se(1) atoms to form a mixture of edge and corner-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles are 12°. There are five inequivalent Se sites. In the first Se site, Se(5) is bonded to two equivalent Cs(1), one Er(1), and two equivalent Er(2) atoms to form distorted SeCs2Er3 trigonal bipyramids that share corners with four equivalent Se(4)Er5 square pyramids, corners with two equivalent Se(3)Cs2Er3 trigonal bipyramids,  an edgeedge with one Se(4)Er5 square pyramid, edges with two equivalent Se(5)Cs2Er3 trigonal bipyramids, edges with two equivalent Se(1)CsEr4 trigonal bipyramids, and edges with three equivalent Se(3)Cs2Er3 trigonal bipyramids. In the second Se site, Se(1) is bonded to one Cs(1), one Er(2), and three equivalent Er(3) atoms to form distorted SeCsEr4 trigonal bipyramids that share  a cornercorner with one Se(4)Er5 square pyramid, corners with two equivalent Se(1)CsEr4 trigonal bipyramids, corners with three equivalent Se(3)Cs2Er3 trigonal bipyramids, edges with two equivalent Se(4)Er5 square pyramids, edges with two equivalent Se(5)Cs2Er3 trigonal bipyramids, and edges with two equivalent Se(1)CsEr4 trigonal bipyramids. In the third Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent Cs(1), one Er(1), and two equivalent Er(3) atoms. In the fourth Se site, Se(3) is bonded to two equivalent Cs(1), one Er(2), and two equivalent Er(1) atoms to form distorted SeCs2Er3 trigonal bipyramids that share corners with four equivalent Se(4)Er5 square pyramids, corners with two equivalent Se(5)Cs2Er3 trigonal bipyramids, corners with three equivalent Se(1)CsEr4 trigonal bipyramids,  an edgeedge with one Se(4)Er5 square pyramid, edges with two equivalent Se(3)Cs2Er3 trigonal bipyramids, and edges with three equivalent Se(5)Cs2Er3 trigonal bipyramids. In the fifth Se site, Se(4) is bonded to one Er(3), two equivalent Er(1), and two equivalent Er(2) atoms to form SeEr5 square pyramids that share  a cornercorner with one Se(1)CsEr4 trigonal bipyramid, corners with four equivalent Se(3)Cs2Er3 trigonal bipyramids, corners with four equivalent Se(5)Cs2Er3 trigonal bipyramids, edges with two equivalent Se(4)Er5 square pyramids,  an edgeedge with one Se(3)Cs2Er3 trigonal bipyramid,  an edgeedge with one Se(5)Cs2Er3 trigonal bipyramid, and edges with two equivalent Se(1)CsEr4 trigonal bipyramids. is represented by the CIF card [CIF]
data_CsEr3Se5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.100
_cell_length_b   12.336
_cell_length_c   21.994
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   1112.404
_cell_formula_units_Z   4
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  0.250  0.854  0.092  1.0
  Cs  Cs1  1  0.750  0.146  0.908  1.0
  Cs  Cs2  1  0.750  0.354  0.408  1.0
  Cs  Cs3  1  0.250  0.646  0.592  1.0
  Er  Er4  1  0.750  0.797  0.825  1.0
  Er  Er5  1  0.250  0.203  0.175  1.0
  Er  Er6  1  0.250  0.297  0.675  1.0
  Er  Er7  1  0.750  0.703  0.325  1.0
  Er  Er8  1  0.250  0.957  0.698  1.0
  Er  Er9  1  0.750  0.043  0.302  1.0
  Er  Er10  1  0.750  0.457  0.802  1.0
  Er  Er11  1  0.250  0.543  0.198  1.0
  Er  Er12  1  0.750  0.392  0.054  1.0
  Er  Er13  1  0.250  0.608  0.946  1.0
  Er  Er14  1  0.250  0.892  0.446  1.0
  Er  Er15  1  0.750  0.108  0.554  1.0
  Se  Se16  1  0.250  0.949  0.569  1.0
  Se  Se17  1  0.750  0.051  0.431  1.0
  Se  Se18  1  0.750  0.449  0.931  1.0
  Se  Se19  1  0.250  0.551  0.069  1.0
  Se  Se20  1  0.750  0.764  0.952  1.0
  Se  Se21  1  0.250  0.236  0.048  1.0
  Se  Se22  1  0.250  0.264  0.548  1.0
  Se  Se23  1  0.750  0.736  0.452  1.0
  Se  Se24  1  0.250  0.950  0.825  1.0
  Se  Se25  1  0.750  0.050  0.175  1.0
  Se  Se26  1  0.750  0.450  0.675  1.0
  Se  Se27  1  0.250  0.550  0.325  1.0
  Se  Se28  1  0.750  0.126  0.685  1.0
  Se  Se29  1  0.250  0.874  0.315  1.0
  Se  Se30  1  0.250  0.626  0.815  1.0
  Se  Se31  1  0.750  0.374  0.185  1.0
  Se  Se32  1  0.750  0.694  0.198  1.0
  Se  Se33  1  0.250  0.306  0.802  1.0
  Se  Se34  1  0.250  0.194  0.302  1.0
  Se  Se35  1  0.750  0.806  0.698  1.0
[/CIF]
.
The compound described by CsEr3Se5 crystallizes in the orthorhombic Pnma space group. Cs(1) is bonded in a 7-coordinate geometry to one Se(1), two equivalent Se(2), two equivalent Se(3), and two equivalent Se(5) atoms. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one Se(2), one Se(5), two equivalent Se(3), and two equivalent Se(4) atoms to form a mixture of edge and corner-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles are 2°. In the second Er site, Er(2) is bonded to one Se(1), one Se(3), two equivalent Se(4), and two equivalent Se(5) atoms to form a mixture of edge and corner-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles range from 2-12°. In the third Er site, Er(3) is bonded to one Se(4), two equivalent Se(2), and three equivalent Se(1) atoms to form a mixture of edge and corner-sharing ErSe6 octahedra. The corner-sharing octahedral tilt angles are 12°. There are five inequivalent Se sites. In the first Se site, Se(5) is bonded to two equivalent Cs(1), one Er(1), and two equivalent Er(2) atoms to form distorted SeCs2Er3 trigonal bipyramids that share corners with four equivalent Se(4)Er5 square pyramids, corners with two equivalent Se(3)Cs2Er3 trigonal bipyramids,  an edgeedge with one Se(4)Er5 square pyramid, edges with two equivalent Se(5)Cs2Er3 trigonal bipyramids, edges with two equivalent Se(1)CsEr4 trigonal bipyramids, and edges with three equivalent Se(3)Cs2Er3 trigonal bipyramids. In the second Se site, Se(1) is bonded to one Cs(1), one Er(2), and three equivalent Er(3) atoms to form distorted SeCsEr4 trigonal bipyramids that share  a cornercorner with one Se(4)Er5 square pyramid, corners with two equivalent Se(1)CsEr4 trigonal bipyramids, corners with three equivalent Se(3)Cs2Er3 trigonal bipyramids, edges with two equivalent Se(4)Er5 square pyramids, edges with two equivalent Se(5)Cs2Er3 trigonal bipyramids, and edges with two equivalent Se(1)CsEr4 trigonal bipyramids. In the third Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent Cs(1), one Er(1), and two equivalent Er(3) atoms. In the fourth Se site, Se(3) is bonded to two equivalent Cs(1), one Er(2), and two equivalent Er(1) atoms to form distorted SeCs2Er3 trigonal bipyramids that share corners with four equivalent Se(4)Er5 square pyramids, corners with two equivalent Se(5)Cs2Er3 trigonal bipyramids, corners with three equivalent Se(1)CsEr4 trigonal bipyramids,  an edgeedge with one Se(4)Er5 square pyramid, edges with two equivalent Se(3)Cs2Er3 trigonal bipyramids, and edges with three equivalent Se(5)Cs2Er3 trigonal bipyramids. In the fifth Se site, Se(4) is bonded to one Er(3), two equivalent Er(1), and two equivalent Er(2) atoms to form SeEr5 square pyramids that share  a cornercorner with one Se(1)CsEr4 trigonal bipyramid, corners with four equivalent Se(3)Cs2Er3 trigonal bipyramids, corners with four equivalent Se(5)Cs2Er3 trigonal bipyramids, edges with two equivalent Se(4)Er5 square pyramids,  an edgeedge with one Se(3)Cs2Er3 trigonal bipyramid,  an edgeedge with one Se(5)Cs2Er3 trigonal bipyramid, and edges with two equivalent Se(1)CsEr4 trigonal bipyramids. is represented by the CIF card [CIF]
data_CsEr3Se5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.100
_cell_length_b   12.336
_cell_length_c   21.994
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   1112.404
_cell_formula_units_Z   4
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  0.250  0.854  0.092  1.0
  Cs  Cs1  1  0.750  0.146  0.908  1.0
  Cs  Cs2  1  0.750  0.354  0.408  1.0
  Cs  Cs3  1  0.250  0.646  0.592  1.0
  Er  Er4  1  0.750  0.797  0.825  1.0
  Er  Er5  1  0.250  0.203  0.175  1.0
  Er  Er6  1  0.250  0.297  0.675  1.0
  Er  Er7  1  0.750  0.703  0.325  1.0
  Er  Er8  1  0.250  0.957  0.698  1.0
  Er  Er9  1  0.750  0.043  0.302  1.0
  Er  Er10  1  0.750  0.457  0.802  1.0
  Er  Er11  1  0.250  0.543  0.198  1.0
  Er  Er12  1  0.750  0.392  0.054  1.0
  Er  Er13  1  0.250  0.608  0.946  1.0
  Er  Er14  1  0.250  0.892  0.446  1.0
  Er  Er15  1  0.750  0.108  0.554  1.0
  Se  Se16  1  0.250  0.949  0.569  1.0
  Se  Se17  1  0.750  0.051  0.431  1.0
  Se  Se18  1  0.750  0.449  0.931  1.0
  Se  Se19  1  0.250  0.551  0.069  1.0
  Se  Se20  1  0.750  0.764  0.952  1.0
  Se  Se21  1  0.250  0.236  0.048  1.0
  Se  Se22  1  0.250  0.264  0.548  1.0
  Se  Se23  1  0.750  0.736  0.452  1.0
  Se  Se24  1  0.250  0.950  0.825  1.0
  Se  Se25  1  0.750  0.050  0.175  1.0
  Se  Se26  1  0.750  0.450  0.675  1.0
  Se  Se27  1  0.250  0.550  0.325  1.0
  Se  Se28  1  0.750  0.126  0.685  1.0
  Se  Se29  1  0.250  0.874  0.315  1.0
  Se  Se30  1  0.250  0.626  0.815  1.0
  Se  Se31  1  0.750  0.374  0.185  1.0
  Se  Se32  1  0.750  0.694  0.198  1.0
  Se  Se33  1  0.250  0.306  0.802  1.0
  Se  Se34  1  0.250  0.194  0.302  1.0
  Se  Se35  1  0.750  0.806  0.698  1.0
[/CIF]
.