data_La2SiSe
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.18
_cell_length_b   5.18
_cell_length_c   5.18
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   La2SiSe
_chemical_formula_sum   'La2 Si1 Se1'
_cell_volume   98.35
_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
  La  La0  1  0.5  0.5  0.5  1.0
  La  La1  1  0.66  0.66  0.66  1.0
  Si  Si3  1  0.0  0.0  0.0  1.0
  Se  Se2  1  0.83  0.83  0.83  1.0

data_La2SiSe
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.18
_cell_length_b   5.18
_cell_length_c   12.69
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   La2SiSe
_chemical_formula_sum   'La6 Si3 Se3'
_cell_volume   295.05
_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
  La  La0  3  0.0  0.0  0.34  1.0
  La  La1  3  0.0  0.0  0.5  1.0
  Si  Si2  3  0.0  0.0  0.0  1.0
  Se  Se3  3  0.0  0.0  0.17  1.0

La La Si Se
La2SiSe crystallizes in the trigonal R3m space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 7-coordinate geometry to one La(2), three equivalent Si(1), and three equivalent Se(1) atoms. The La(1)-La(2) bond length is 2.13 Å. All La(1)-Si(1) bond lengths are 3.63 Å. All La(1)-Se(1) bond lengths are 2.99 Å. In the second La site, La(2) is bonded in a distorted single-bond geometry to one La(1) and one Se(1) atom. The La(2)-Se(1) bond length is 2.13 Å. Si(1) is bonded in a 1-coordinate geometry to three equivalent La(1) and one Se(1) atom. The Si(1)-Se(1) bond length is 2.13 Å. Se(1) is bonded to one La(2), three equivalent La(1), and one Si(1) atom to form distorted corner-sharing SeLa4Si trigonal bipyramids.