data_Mn2NiSe
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.26
_cell_length_b   3.26
_cell_length_c   5.38
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Mn2NiSe
_chemical_formula_sum   'Mn2 Ni1 Se1'
_cell_volume   57.05
_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
  Mn  Mn0  1  0.63  0.63  0.08  1.0
  Mn  Mn1  1  0.63  0.63  0.3  1.0
  Ni  Ni2  1  0.0  0.0  0.0  1.0
  Se  Se3  1  0.0  0.0  0.69  1.0

data_Mn2NiSe
_symmetry_space_group_name_H-M   Cm
_cell_length_a   4.6
_cell_length_b   4.6
_cell_length_c   5.38
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   Mn2NiSe
_chemical_formula_sum   'Mn4 Ni2 Se2'
_cell_volume   114.09
_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
  Mn  Mn0  2  0.13  0.5  0.08  1.0
  Mn  Mn1  2  0.13  0.5  0.3  1.0
  Ni  Ni2  2  0.0  0.0  0.0  1.0
  Se  Se3  2  0.0  0.0  0.69  1.0

Mn Mn Ni Se
Mn2NiSe crystallizes in the monoclinic Cm space group. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded in a 4-coordinate geometry to one Mn(2) and three equivalent Ni(1) atoms. The Mn(1)-Mn(2) bond length is 1.22 Å. There is one shorter (1.76 Å) and two longer (2.41 Å) Mn(1)-Ni(1) bond lengths. In the second Mn site, Mn(2) is bonded in a 2-coordinate geometry to one Mn(1) and one Se(1) atom. The Mn(2)-Se(1) bond length is 2.70 Å. Ni(1) is bonded in a 2-coordinate geometry to three equivalent Mn(1) and one Se(1) atom. The Ni(1)-Se(1) bond length is 1.67 Å. Se(1) is bonded in a distorted single-bond geometry to one Mn(2) and one Ni(1) atom.