data_CaSi2Se
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.9
_cell_length_b   4.9
_cell_length_c   4.9
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   CaSi2Se
_chemical_formula_sum   'Ca1 Si2 Se1'
_cell_volume   82.95
_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
  Ca  Ca0  1  0.46  0.46  0.46  1.0
  Si  Si2  1  0.0  0.0  0.0  1.0
  Si  Si3  1  0.73  0.73  0.73  1.0
  Se  Se1  1  0.19  0.19  0.19  1.0

data_CaSi2Se
_symmetry_space_group_name_H-M   R3m
_cell_length_a   4.9
_cell_length_b   4.9
_cell_length_c   11.99
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   CaSi2Se
_chemical_formula_sum   'Ca3 Si6 Se3'
_cell_volume   248.85
_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
  Ca  Ca0  3  0.0  0.0  0.54  1.0
  Si  Si1  3  0.0  0.0  0.0  1.0
  Si  Si2  3  0.0  0.0  0.27  1.0
  Se  Se3  3  0.0  0.0  0.81  1.0

Ca Si Si Se
CaSi2Se crystallizes in the trigonal R3m space group. Ca(1) is bonded in a 11-coordinate geometry to three equivalent Si(1), four equivalent Si(2), and four equivalent Se(1) atoms. All Ca(1)-Si(1) bond lengths are 3.22 Å. There are three shorter (2.93 Å) and one longer (3.23 Å) Ca(1)-Si(2) bond length. There are three shorter (2.93 Å) and one longer (3.23 Å) Ca(1)-Se(1) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a single-bond geometry to three equivalent Ca(1) and one Se(1) atom. The Si(1)-Se(1) bond length is 2.31 Å. In the second Si site, Si(2) is bonded to four equivalent Ca(1) atoms to form distorted corner-sharing SiCa4 tetrahedra. Se(1) is bonded in a 5-coordinate geometry to four equivalent Ca(1) and one Si(1) atom.