data_FeAs2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.32
_cell_length_b   6.32
_cell_length_c   6.32
_cell_angle_alpha   153.95
_cell_angle_beta   153.95
_cell_angle_gamma   37.17
_symmetry_Int_Tables_number   1
_chemical_formula_structural   FeAs2
_chemical_formula_sum   'Fe1 As2'
_cell_volume   48.63
_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
  Fe  Fe2  1  0.0  0.0  0.0  1.0
  As  As0  1  0.0  0.0  0.51  1.0
  As  As1  1  0.0  0.0  0.47  1.0

data_FeAs2
_symmetry_space_group_name_H-M   Cm
_cell_length_a   4.03
_cell_length_b   4.03
_cell_length_c   6.32
_cell_angle_alpha   90.0
_cell_angle_beta   108.59
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   FeAs2
_chemical_formula_sum   'Fe2 As4'
_cell_volume   97.26
_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
  Fe  Fe0  2  0.0  0.0  0.0  1.0
  As  As1  2  0.0  0.0  0.49  1.0
  As  As2  2  0.0  0.0  0.53  1.0

Fe As As
Fe As As 0 0 + o + 0 0 o + + 0 2 o o - 0 2 o o o 0 1 o o - 0 1 o o o 1 2 o o o 
FeAs2 crystallizes in the monoclinic Cm space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to four equivalent Fe(1), one As(1), and one As(2) atom to form a mixture of distorted corner and edge-sharing FeFe4As2 octahedra. The corner-sharing octahedra are not tilted. All Fe(1)-Fe(1) bond lengths are 2.85 Å. The Fe(1)-As(1) bond length is 3.11 Å. The Fe(1)-As(2) bond length is 3.00 Å. In the second Fe site, Fe(1) is bonded to four equivalent Fe(1), one As(1), and one As(2) atom to form a mixture of distorted corner and edge-sharing FeFe4As2 octahedra. The corner-sharing octahedra are not tilted. The Fe(1)-As(1) bond length is 3.11 Å. The Fe(1)-As(2) bond length is 3.00 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded in a single-bond geometry to one Fe(1) and one As(2) atom. The As(1)-As(2) bond length is 0.20 Å. In the second As site, As(2) is bonded in a single-bond geometry to one Fe(1) and one As(1) atom.