data_Tl2FeSe
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.16
_cell_length_b   5.16
_cell_length_c   5.16
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Tl2FeSe
_chemical_formula_sum   'Tl2 Fe1 Se1'
_cell_volume   96.97
_cell_formula_units_Z   1
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
  Tl  Tl2  1  0.65  0.65  0.65  1.0
  Tl  Tl3  1  0.82  0.82  0.82  1.0
  Fe  Fe0  1  0.0  0.0  0.0  1.0
  Se  Se1  1  0.47  0.47  0.47  1.0

data_Tl2FeSe
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.16
_cell_length_b   5.16
_cell_length_c   12.63
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   Tl2FeSe
_chemical_formula_sum   'Tl6 Fe3 Se3'
_cell_volume   290.92
_cell_formula_units_Z   3
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-y, x-y, z'
  3  '-x+y, -x, z'
  4  '-y, -x, z'
  5  '-x+y, y, z'
  6  'x, x-y, z'
  7  'x+1/3, y+2/3, z+2/3'
  8  '-y+1/3, x-y+2/3, z+2/3'
  9  '-x+y+1/3, -x+2/3, z+2/3'
  10  '-y+1/3, -x+2/3, z+2/3'
  11  '-x+y+1/3, y+2/3, z+2/3'
  12  'x+1/3, x-y+2/3, z+2/3'
  13  'x+2/3, y+1/3, z+1/3'
  14  '-y+2/3, x-y+1/3, z+1/3'
  15  '-x+y+2/3, -x+1/3, z+1/3'
  16  '-y+2/3, -x+1/3, z+1/3'
  17  '-x+y+2/3, y+1/3, z+1/3'
  18  'x+2/3, x-y+1/3, z+1/3'
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
  Tl  Tl0  3  0.0  0.0  0.18  1.0
  Tl  Tl1  3  0.0  0.0  0.35  1.0
  Fe  Fe2  3  0.0  0.0  0.0  1.0
  Se  Se3  3  0.0  0.0  0.53  1.0

Tl Tl Fe Se
FeTl2Se crystallizes in the trigonal R3m space group. Fe(1) is bonded to one Tl(2) and three equivalent Tl(1) atoms to form distorted FeTl4 trigonal pyramids that share corners with three equivalent Tl(2)TlFeSe3 trigonal bipyramids, corners with six equivalent Fe(1)Tl4 trigonal pyramids, and edges with three equivalent Se(1)Tl4 trigonal pyramids. The Fe(1)-Tl(2) bond length is 2.23 Å. All Fe(1)-Tl(1) bond lengths are 2.99 Å. There are two inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a distorted single-bond geometry to three equivalent Fe(1), one Tl(2), and one Se(1) atom. The Tl(1)-Tl(2) bond length is 2.23 Å. The Tl(1)-Se(1) bond length is 2.23 Å. In the second Tl site, Tl(2) is bonded to one Fe(1), one Tl(1), and three equivalent Se(1) atoms to form distorted TlTlFeSe3 trigonal bipyramids that share corners with six equivalent Tl(2)TlFeSe3 trigonal bipyramids,  a cornercorner with one Se(1)Tl4 trigonal pyramid, and corners with three equivalent Fe(1)Tl4 trigonal pyramids. All Tl(2)-Se(1) bond lengths are 2.99 Å. Se(1) is bonded to one Tl(1) and three equivalent Tl(2) atoms to form distorted SeTl4 trigonal pyramids that share  a cornercorner with one Tl(2)TlFeSe3 trigonal bipyramid, corners with six equivalent Se(1)Tl4 trigonal pyramids, and edges with three equivalent Fe(1)Tl4 trigonal pyramids.