data_FeAs
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.4
_cell_length_b   3.32
_cell_length_c   6.0
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   FeAs
_chemical_formula_sum   'Fe4 As4'
_cell_volume   107.31
_cell_formula_units_Z   4
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  Fe0  1  0.4  0.49  0.8  1.0
  Fe  Fe1  1  0.0  0.83  0.2  1.0
  Fe  Fe2  1  0.7  0.49  0.2  1.0
  Fe  Fe3  1  0.7  0.83  0.8  1.0
  As  As4  1  0.32  0.49  0.54  1.0
  As  As5  1  0.08  0.83  0.45  1.0
  As  As6  1  0.62  0.49  0.46  1.0
  As  As7  1  0.77  0.83  0.54  1.0

data_FeAs
_symmetry_space_group_name_H-M   P-1
_cell_length_a   3.32
_cell_length_b   5.4
_cell_length_c   6.0
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   2
_chemical_formula_structural   FeAs
_chemical_formula_sum   'Fe4 As4'
_cell_volume   107.31
_cell_formula_units_Z   4
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-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  Fe0  2  0.17  0.0  0.8  1.0
  Fe  Fe1  2  0.17  0.3  0.2  1.0
  As  As2  2  0.17  0.08  0.54  1.0
  As  As3  2  0.17  0.38  0.46  1.0

Fe Fe Fe Fe As As As As
FeAs crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of four arsanylidyneiron molecules. Fe(1) is bonded in a distorted single-bond geometry to one As(1) atom. The Fe(1)-As(1) bond length is 1.58 Å. As(1) is bonded in a distorted single-bond geometry to one Fe(1) atom.