data_Ba2AlCu
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.49
_cell_length_b   5.49
_cell_length_c   5.49
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Ba2AlCu
_chemical_formula_sum   'Ba2 Al1 Cu1'
_cell_volume   116.76
_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
  Ba  Ba1  1  0.88  0.88  0.88  1.0
  Ba  Ba2  1  0.82  0.82  0.82  1.0
  Al  Al0  1  0.0  0.0  0.0  1.0
  Cu  Cu3  1  0.94  0.94  0.94  1.0

data_Ba2AlCu
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.49
_cell_length_b   5.49
_cell_length_c   13.44
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   Ba2AlCu
_chemical_formula_sum   'Ba6 Al3 Cu3'
_cell_volume   350.28
_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
  Ba  Ba0  3  0.0  0.0  0.12  1.0
  Ba  Ba1  3  0.0  0.0  0.18  1.0
  Al  Al2  3  0.0  0.0  0.0  1.0
  Cu  Cu3  3  0.0  0.0  0.06  1.0

Ba Ba Al Cu
Ba2CuAl crystallizes in the trigonal R3m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a distorted linear geometry to one Ba(2) and one Cu(1) atom. The Ba(1)-Ba(2) bond length is 0.81 Å. The Ba(1)-Cu(1) bond length is 0.81 Å. In the second Ba site, Ba(2) is bonded in a distorted rectangular see-saw-like geometry to one Ba(1) and three equivalent Al(1) atoms. All Ba(2)-Al(1) bond lengths are 3.77 Å. Cu(1) is bonded in a linear geometry to one Ba(1) and one Al(1) atom. The Cu(1)-Al(1) bond length is 0.81 Å. Al(1) is bonded in a single-bond geometry to three equivalent Ba(2) and one Cu(1) atom.