data_FeSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.34
_cell_length_b   6.34
_cell_length_c   6.34
_cell_angle_alpha   137.17
_cell_angle_beta   137.17
_cell_angle_gamma   62.17
_symmetry_Int_Tables_number   1
_chemical_formula_structural   FeSe4
_chemical_formula_sum   'Fe1 Se4'
_cell_volume   116.24
_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
  Fe  Fe0  1  0.0  0.0  0.0  1.0
  Se  Se1  1  0.31  0.0  0.71  1.0
  Se  Se2  1  0.0  0.31  0.71  1.0
  Se  Se3  1  0.0  0.0  0.6  1.0
  Se  Se4  1  0.0  0.0  0.25  1.0

data_FeSe4
_symmetry_space_group_name_H-M   Cm
_cell_length_a   6.54
_cell_length_b   6.54
_cell_length_c   6.34
_cell_angle_alpha   90.0
_cell_angle_beta   121.09
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   FeSe4
_chemical_formula_sum   'Fe2 Se8'
_cell_volume   232.48
_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
  Fe  Fe0  2  0.0  0.0  0.0  1.0
  Se  Se1  4  0.44  0.16  0.6  1.0
  Se  Se2  2  0.25  0.5  0.75  1.0
  Se  Se3  2  0.4  0.0  0.4  1.0

Fe Se Se Se Se
FeSe4 crystallizes in the monoclinic Cm space group. Fe(1) is bonded in a distorted linear geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. The Fe(1)-Se(2) bond length is 2.53 Å. The Fe(1)-Se(3) bond length is 1.61 Å. Both Fe(1)-Se(1) bond lengths are 3.26 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Fe(1), one Se(1), one Se(2), and two equivalent Se(3) atoms. The Se(1)-Se(1) bond length is 2.05 Å. The Se(1)-Se(2) bond length is 1.54 Å. There is one shorter (1.99 Å) and one longer (2.97 Å) Se(1)-Se(3) bond length. In the second Se site, Se(2) is bonded in a 3-coordinate geometry to one Fe(1) and two equivalent Se(1) atoms. In the third Se site, Se(3) is bonded in a single-bond geometry to one Fe(1) and four equivalent Se(1) atoms.