data_NiAs
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.07
_cell_length_b   3.07
_cell_length_c   7.93
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   NiAs
_chemical_formula_sum   'Ni2 As2'
_cell_volume   64.57
_cell_formula_units_Z   2
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  Ni2  1  0.53  0.89  0.05  1.0
  Ni  Ni3  1  0.0  0.77  0.88  1.0
  As  As0  1  0.53  0.89  0.41  1.0
  As  As1  1  0.0  0.77  0.53  1.0

data_NiAs
_symmetry_space_group_name_H-M   P-1
_cell_length_a   3.07
_cell_length_b   3.07
_cell_length_c   7.93
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   2
_chemical_formula_structural   NiAs
_chemical_formula_sum   'Ni2 As2'
_cell_volume   64.57
_cell_formula_units_Z   2
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
  Ni  Ni0  2  0.27  0.56  0.59  1.0
  As  As1  2  0.27  0.56  0.94  1.0

Ni Ni As As
Ni Ni As As 0 1 o o - 0 1 + o - 2 3 o o o 2 3 + o o 
NiAs crystallizes in the triclinic P-1 space group. Ni(1) is bonded in a 3-coordinate geometry to two equivalent Ni(1) and one As(1) atom. There is one shorter (2.05 Å) and one longer (2.15 Å) Ni(1)-Ni(1) bond length. The Ni(1)-As(1) bond length is 2.79 Å. As(1) is bonded in a 4-coordinate geometry to one Ni(1) and three equivalent As(1) atoms. There are a spread of As(1)-As(1) bond distances ranging from 1.77-2.54 Å.