data_NiSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.5
_cell_length_b   6.5
_cell_length_c   6.5
_cell_angle_alpha   138.03
_cell_angle_beta   138.03
_cell_angle_gamma   60.86
_symmetry_Int_Tables_number   1
_chemical_formula_structural   NiSe4
_chemical_formula_sum   'Ni1 Se4'
_cell_volume   121.31
_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
  Ni  Ni0  1  0.0  0.0  0.0  1.0
  Se  Se1  1  0.33  0.0  0.8  1.0
  Se  Se2  1  0.0  0.33  0.8  1.0
  Se  Se3  1  0.0  0.0  0.87  1.0
  Se  Se4  1  0.0  0.0  0.33  1.0

data_NiSe4
_symmetry_space_group_name_H-M   Cm
_cell_length_a   6.58
_cell_length_b   6.58
_cell_length_c   6.5
_cell_angle_alpha   90.0
_cell_angle_beta   120.43
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   NiSe4
_chemical_formula_sum   'Ni2 Se8'
_cell_volume   242.61
_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
  Ni  Ni0  2  0.0  0.0  0.0  1.0
  Se  Se1  4  0.34  0.34  0.47  1.0
  Se  Se2  2  0.0  0.0  0.33  1.0
  Se  Se3  2  0.0  0.0  0.87  1.0

Ni Se Se Se Se
NiSe4 crystallizes in the monoclinic Cm space group. Ni(1) is bonded in a linear geometry to one Se(2) and one Se(3) atom. The Ni(1)-Se(2) bond length is 0.84 Å. The Ni(1)-Se(3) bond length is 2.16 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to one Se(1), one Se(2), and two equivalent Se(3) atoms. The Se(1)-Se(1) bond length is 2.15 Å. The Se(1)-Se(2) bond length is 2.48 Å. There is one shorter (2.04 Å) and one longer (2.93 Å) Se(1)-Se(3) bond length. In the second Se site, Se(2) is bonded in a single-bond geometry to one Ni(1) and two equivalent Se(1) atoms. In the third Se site, Se(3) is bonded in a distorted single-bond geometry to one Ni(1) and four equivalent Se(1) atoms.