data_UNi3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.66
_cell_length_b   4.66
_cell_length_c   4.66
_cell_angle_alpha   132.88
_cell_angle_beta   132.88
_cell_angle_gamma   68.84
_symmetry_Int_Tables_number   1
_chemical_formula_structural   UNi3
_chemical_formula_sum   'U1 Ni3'
_cell_volume   53.49
_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
  U  U3  1  0.0  0.0  0.85  1.0
  Ni  Ni0  1  0.86  0.0  0.92  1.0
  Ni  Ni1  1  0.0  0.86  0.92  1.0
  Ni  Ni2  1  0.0  0.0  0.0  1.0

data_UNi3
_symmetry_space_group_name_H-M   Cm
_cell_length_a   5.27
_cell_length_b   5.27
_cell_length_c   4.66
_cell_angle_alpha   90.0
_cell_angle_beta   124.42
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   UNi3
_chemical_formula_sum   'U2 Ni6'
_cell_volume   106.98
_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
  U  U0  2  0.0  0.0  0.85  1.0
  Ni  Ni1  4  0.07  0.07  0.06  1.0
  Ni  Ni2  2  0.0  0.0  0.0  1.0

U Ni Ni Ni
UNi3 is alpha Niobium phosphide-derived structured and crystallizes in the monoclinic Cm space group. The structure is zero-dimensional and consists of two UNi3 clusters. U(1) is bonded in a distorted single-bond geometry to one Ni(2) atom. The U(1)-Ni(2) bond length is 0.71 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a distorted single-bond geometry to one Ni(2) atom. The Ni(1)-Ni(2) bond length is 0.47 Å. In the second Ni site, Ni(2) is bonded in a distorted trigonal non-coplanar geometry to one U(1) and two equivalent Ni(1) atoms.