data_NaNi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.19
_cell_length_b   4.19
_cell_length_c   4.19
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   NaNi2
_chemical_formula_sum   'Na1 Ni2'
_cell_volume   51.88
_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
  Na  Na0  1  0.0  0.0  0.0  1.0
  Ni  Ni1  1  0.44  0.44  0.44  1.0
  Ni  Ni2  1  0.48  0.48  0.48  1.0

data_NaNi2
_symmetry_space_group_name_H-M   R3m
_cell_length_a   4.19
_cell_length_b   4.19
_cell_length_c   10.25
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   NaNi2
_chemical_formula_sum   'Na3 Ni6'
_cell_volume   155.65
_cell_formula_units_Z   3
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-y, x-y, z'
  3  '-x+y, -x, z'
  4  '-y, -x, z'
  5  '-x+y, y, z'
  6  'x, x-y, z'
  7  'x+1/3, y+2/3, z+2/3'
  8  '-y+1/3, x-y+2/3, z+2/3'
  9  '-x+y+1/3, -x+2/3, z+2/3'
  10  '-y+1/3, -x+2/3, z+2/3'
  11  '-x+y+1/3, y+2/3, z+2/3'
  12  'x+1/3, x-y+2/3, z+2/3'
  13  'x+2/3, y+1/3, z+1/3'
  14  '-y+2/3, x-y+1/3, z+1/3'
  15  '-x+y+2/3, -x+1/3, z+1/3'
  16  '-y+2/3, -x+1/3, z+1/3'
  17  '-x+y+2/3, y+1/3, z+1/3'
  18  'x+2/3, x-y+1/3, z+1/3'
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
  Na  Na0  3  0.0  0.0  0.0  1.0
  Ni  Ni1  3  0.0  0.0  0.52  1.0
  Ni  Ni2  3  0.0  0.0  0.56  1.0

Na Ni Ni
NaNi2 crystallizes in the trigonal R3m space group. Na(1) is bonded to three equivalent Ni(1) and three equivalent Ni(2) atoms to form distorted NaNi6 octahedra that share corners with three equivalent Ni(1)Na3Ni tetrahedra and edges with six equivalent Na(1)Ni6 octahedra. All Na(1)-Ni(1) bond lengths are 2.65 Å. All Na(1)-Ni(2) bond lengths are 3.08 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to three equivalent Na(1) and one Ni(2) atom to form distorted NiNa3Ni tetrahedra that share corners with three equivalent Na(1)Ni6 octahedra and corners with six equivalent Ni(1)Na3Ni tetrahedra. The corner-sharing octahedral tilt angles are 52°. The Ni(1)-Ni(2) bond length is 0.41 Å. In the second Ni site, Ni(2) is bonded in a distorted single-bond geometry to three equivalent Na(1) and one Ni(1) atom.