data_BaSiSe2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.78
_cell_length_b   3.78
_cell_length_c   7.32
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   BaSiSe2
_chemical_formula_sum   'Ba1 Si1 Se2'
_cell_volume   104.53
_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
  Ba  Ba0  1  0.0  0.0  0.66  1.0
  Si  Si3  1  0.0  0.0  0.0  1.0
  Se  Se1  1  0.89  0.89  0.71  1.0
  Se  Se2  1  0.89  0.89  0.6  1.0

data_BaSiSe2
_symmetry_space_group_name_H-M   Cm
_cell_length_a   5.35
_cell_length_b   5.35
_cell_length_c   7.32
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   BaSiSe2
_chemical_formula_sum   'Ba2 Si2 Se4'
_cell_volume   209.07
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  'x, -y, z'
  3  'x+1/2, y+1/2, z'
  4  'x+1/2, -y+1/2, 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
  Ba  Ba0  2  0.0  0.0  0.66  1.0
  Si  Si1  2  0.0  0.0  0.0  1.0
  Se  Se2  2  0.39  0.5  0.6  1.0
  Se  Se3  2  0.39  0.5  0.71  1.0

Ba Si Se Se
Ba Si Se Se 0 3 - - o 0 2 - - o 0 1 o o + 1 2 - - - 2 3 o o o 
BaSiSe2 crystallizes in the monoclinic Cm space group. The structure is zero-dimensional and consists of two BaSiSe2 clusters. Ba(1) is bonded in a 2-coordinate geometry to one Se(1) and one Se(2) atom. The Ba(1)-Se(1) bond length is 0.72 Å. The Ba(1)-Se(2) bond length is 0.72 Å. Si(1) is bonded in a single-bond geometry to one Se(1) atom. The Si(1)-Se(1) bond length is 2.17 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a single-bond geometry to one Ba(1) and one Si(1) atom. In the second Se site, Se(2) is bonded in a distorted single-bond geometry to one Ba(1) atom.