data_BaSi2As
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.17
_cell_length_b   5.17
_cell_length_c   5.17
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   BaSi2As
_chemical_formula_sum   'Ba1 Si2 As1'
_cell_volume   97.98
_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  0.66  0.66  0.66  1.0
  Si  Si2  1  0.49  0.49  0.49  1.0
  Si  Si3  1  0.83  0.83  0.83  1.0
  As  As0  1  0.0  0.0  0.0  1.0

data_BaSi2As
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.17
_cell_length_b   5.17
_cell_length_c   12.68
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   BaSi2As
_chemical_formula_sum   'Ba3 Si6 As3'
_cell_volume   293.93
_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  0.34  1.0
  Si  Si1  3  0.0  0.0  0.17  1.0
  Si  Si2  3  0.0  0.0  0.51  1.0
  As  As3  3  0.0  0.0  0.0  1.0

Ba Si Si As
Ba Si Si As 0 1 o o o 0 2 o o o 2 3 + + + 
BaSi2As crystallizes in the trigonal R3m space group. Ba(1) is bonded to one Si(1), one Si(2), and three equivalent As(1) atoms to form distorted BaSi2As3 trigonal bipyramids that share corners with six equivalent Ba(1)Si2As3 trigonal bipyramids and  a cornercorner with one As(1)Ba3Si trigonal pyramid. The Ba(1)-Si(1) bond length is 2.16 Å. The Ba(1)-Si(2) bond length is 2.16 Å. All Ba(1)-As(1) bond lengths are 2.99 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a single-bond geometry to one Ba(1) atom. In the second Si site, Si(2) is bonded in a linear geometry to one Ba(1) and one As(1) atom. The Si(2)-As(1) bond length is 2.16 Å. As(1) is bonded to three equivalent Ba(1) and one Si(2) atom to form AsBa3Si trigonal pyramids that share  a cornercorner with one Ba(1)Si2As3 trigonal bipyramid and corners with six equivalent As(1)Ba3Si trigonal pyramids.