data_Nb2AlCu
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.38
_cell_length_b   3.38
_cell_length_c   5.75
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Nb2AlCu
_chemical_formula_sum   'Nb2 Al1 Cu1'
_cell_volume   65.75
_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
  Nb  Nb2  1  0.0  0.0  0.07  1.0
  Nb  Nb3  1  0.69  0.69  0.4  1.0
  Al  Al0  1  0.0  0.0  0.93  1.0
  Cu  Cu1  1  0.69  0.69  0.23  1.0

data_Nb2AlCu
_symmetry_space_group_name_H-M   Cm
_cell_length_a   4.78
_cell_length_b   4.78
_cell_length_c   5.75
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   Nb2AlCu
_chemical_formula_sum   'Nb4 Al2 Cu2'
_cell_volume   131.51
_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
  Nb  Nb0  2  0.0  0.0  0.07  1.0
  Nb  Nb1  2  0.19  0.5  0.4  1.0
  Al  Al2  2  0.0  0.0  0.93  1.0
  Cu  Cu3  2  0.19  0.5  0.23  1.0

Nb Nb Al Cu
Nb Nb Al Cu 0 2 o o - 1 3 o o o 
Nb2CuAl crystallizes in the monoclinic Cm space group. The structure is zero-dimensional and consists of two Nb2CuAl clusters. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a distorted bent 120 degrees geometry to one Cu(1) and one Al(1) atom. The Nb(1)-Cu(1) bond length is 1.74 Å. The Nb(1)-Al(1) bond length is 0.80 Å. In the second Nb site, Nb(2) is bonded in a single-bond geometry to one Cu(1) atom. The Nb(2)-Cu(1) bond length is 0.97 Å. Cu(1) is bonded in a distorted bent 120 degrees geometry to one Nb(1) and one Nb(2) atom. Al(1) is bonded in a single-bond geometry to one Nb(1) atom.