data_Tl2SiSe
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.23
_cell_length_b   5.23
_cell_length_c   5.23
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Tl2SiSe
_chemical_formula_sum   'Tl2 Si1 Se1'
_cell_volume   101.19
_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  0.55  0.55  0.55  1.0
  Tl  Tl3  1  0.7  0.7  0.7  1.0
  Si  Si1  1  0.0  0.0  0.0  1.0
  Se  Se0  1  0.85  0.85  0.85  1.0

data_Tl2SiSe
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.23
_cell_length_b   5.23
_cell_length_c   12.81
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   Tl2SiSe
_chemical_formula_sum   'Tl6 Si3 Se3'
_cell_volume   303.58
_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  0.3  1.0
  Tl  Tl1  3  0.0  0.0  0.45  1.0
  Si  Si2  3  0.0  0.0  0.0  1.0
  Se  Se3  3  0.0  0.0  0.15  1.0

Tl Tl Si Se
Tl2SiSe crystallizes in the trigonal R3m space group. There are two inequivalent Tl sites. In the first Tl site, Tl(1) is bonded to one Tl(2) and three equivalent Se(1) atoms to form corner-sharing TlTlSe3 trigonal pyramids. The Tl(1)-Tl(2) bond length is 1.93 Å. All Tl(1)-Se(1) bond lengths are 3.05 Å. In the second Tl site, Tl(2) is bonded in a distorted single-bond geometry to one Tl(1) and one Se(1) atom. The Tl(2)-Se(1) bond length is 1.93 Å. Si(1) is bonded in a single-bond geometry to one Se(1) atom. The Si(1)-Se(1) bond length is 1.93 Å. Se(1) is bonded in a distorted linear geometry to one Tl(2), three equivalent Tl(1), and one Si(1) atom.