data_Fe2As
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.88
_cell_length_b   4.88
_cell_length_c   4.88
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Fe2As
_chemical_formula_sum   'Fe4 As2'
_cell_volume   82.22
_cell_formula_units_Z   2
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
  Fe  Fe2  1  0.31  0.59  0.59  1.0
  Fe  Fe3  1  0.31  0.31  0.31  1.0
  Fe  Fe4  1  0.59  0.59  0.31  1.0
  Fe  Fe5  1  0.59  0.31  0.59  1.0
  As  As0  1  0.73  0.73  0.73  1.0
  As  As1  1  0.0  0.0  0.0  1.0

data_Fe2As
_symmetry_space_group_name_H-M   R3m
_cell_length_a   4.88
_cell_length_b   4.88
_cell_length_c   11.96
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   Fe2As
_chemical_formula_sum   'Fe12 As6'
_cell_volume   246.67
_cell_formula_units_Z   6
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
  Fe  Fe0  9  0.18  0.09  0.5  1.0
  Fe  Fe1  3  0.0  0.0  0.69  1.0
  As  As2  3  0.0  0.0  0.0  1.0
  As  As3  3  0.0  0.0  0.27  1.0

Fe Fe Fe Fe As As
Fe Fe Fe Fe As As 0 3 o o o 0 2 o o o 0 1 o o o 0 4 o o o 0 4 - o o 0 5 o + + 0 5 o + o 0 5 o o + 1 5 o o + 1 5 o + o 1 5 + o o 1 3 o o o 1 2 o o o 1 4 o o - 1 4 o - o 1 4 - o o 2 3 o o o 2 4 o o o 2 4 o o - 2 5 + + o 2 5 + o o 2 5 o + o 3 4 o o o 3 4 o - o 3 5 + o + 3 5 + o o 3 5 o o + 4 5 o + + 4 5 + o + 4 5 + + o 4 5 + + + 
Fe2As crystallizes in the trigonal R3m space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 3-coordinate geometry to two equivalent Fe(1), three equivalent Fe(2), one As(1), and one As(2) atom. Both Fe(1)-Fe(1) bond lengths are 1.34 Å. There is one shorter (2.32 Å) and two longer (3.10 Å) Fe(1)-Fe(2) bond lengths. The Fe(1)-As(1) bond length is 2.40 Å. The Fe(1)-As(2) bond length is 2.88 Å. In the second Fe site, Fe(2) is bonded in a 15-coordinate geometry to nine equivalent Fe(1), three equivalent As(1), and three equivalent As(2) atoms. All Fe(2)-As(1) bond lengths are 2.97 Å. All Fe(2)-As(2) bond lengths are 2.83 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 3-coordinate geometry to three equivalent Fe(1) and three equivalent Fe(2) atoms. In the second As site, As(2) is bonded in a 6-coordinate geometry to three equivalent Fe(1) and three equivalent Fe(2) atoms.