data_FeCu2Se
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.27
_cell_length_b   3.42
_cell_length_c   4.99
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   FeCu2Se
_chemical_formula_sum   'Fe1 Cu2 Se1'
_cell_volume   55.84
_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  Fe2  1  0.0  0.0  0.0  1.0
  Cu  Cu0  1  0.63  0.71  0.79  1.0
  Cu  Cu1  1  0.63  0.71  0.2  1.0
  Se  Se3  1  0.0  0.0  0.5  1.0

data_FeCu2Se
_symmetry_space_group_name_H-M   Pm
_cell_length_a   3.27
_cell_length_b   4.99
_cell_length_c   3.42
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   6
_chemical_formula_structural   FeCu2Se
_chemical_formula_sum   'Fe1 Cu2 Se1'
_cell_volume   55.84
_cell_formula_units_Z   1
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '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
  Cu  Cu1  2  0.63  0.21  0.71  1.0
  Se  Se2  1  0.0  0.5  0.0  1.0

Fe Cu Cu Se
Fe Cu Cu Se 0 1 - - - 0 2 - - o 0 3 o o o 0 3 o o - 1 3 + + o 1 2 o o + 2 3 + + o 
FeCu2Se crystallizes in the triclinic P1 space group. Fe(1) is bonded in a 2-coordinate geometry to one Cu(1), one Cu(2), and two equivalent Se(1) atoms. The Fe(1)-Cu(1) bond length is 1.87 Å. The Fe(1)-Cu(2) bond length is 1.84 Å. There is one shorter (2.48 Å) and one longer (2.52 Å) Fe(1)-Se(1) bond length. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 2-coordinate geometry to one Fe(1) and three equivalent Se(1) atoms. There are a spread of Cu(1)-Se(1) bond distances ranging from 2.14-3.09 Å. In the second Cu site, Cu(2) is bonded in a 2-coordinate geometry to one Fe(1) and three equivalent Se(1) atoms. There are a spread of Cu(2)-Se(1) bond distances ranging from 2.14-3.09 Å. Se(1) is bonded in a 8-coordinate geometry to two equivalent Fe(1), three equivalent Cu(1), and three equivalent Cu(2) atoms.