data_Ca(FeAs)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.43
_cell_length_b   6.43
_cell_length_c   6.43
_cell_angle_alpha   145.37
_cell_angle_beta   145.37
_cell_angle_gamma   49.78
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Ca(FeAs)2
_chemical_formula_sum   'Ca1 Fe2 As2'
_cell_volume   85.36
_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
  Ca  Ca2  1  0.0  0.0  0.0  1.0
  Fe  Fe3  1  0.91  0.0  0.92  1.0
  Fe  Fe4  1  0.0  0.91  0.92  1.0
  As  As0  1  0.0  0.0  0.47  1.0
  As  As1  1  0.0  0.0  0.19  1.0

data_Ca(FeAs)2
_symmetry_space_group_name_H-M   Cm
_cell_length_a   5.41
_cell_length_b   5.41
_cell_length_c   6.43
_cell_angle_alpha   90.0
_cell_angle_beta   114.89
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   Ca(FeAs)2
_chemical_formula_sum   'Ca2 Fe4 As4'
_cell_volume   170.72
_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
  Ca  Ca0  2  0.0  0.0  0.0  1.0
  Fe  Fe1  4  0.46  0.46  0.0  1.0
  As  As2  2  0.19  0.0  0.19  1.0
  As  As3  2  0.47  0.0  0.47  1.0

Ca Fe Fe As As
Ca Fe Fe As As 0 1 - o - 0 2 o - - 0 4 o o o 1 4 + o + 2 4 o + + 3 4 o o o 
CaFe2As2 crystallizes in the monoclinic Cm space group. The structure is zero-dimensional and consists of two CaFe2As2 clusters. Ca(1) is bonded in a distorted L-shaped geometry to two equivalent Fe(1) and one As(2) atom. Both Ca(1)-Fe(1) bond lengths are 0.33 Å. The Ca(1)-As(2) bond length is 1.24 Å. Fe(1) is bonded in a single-bond geometry to one Ca(1) atom. There are two inequivalent As sites. In the first As site, As(1) is bonded in a single-bond geometry to one As(2) atom. The As(1)-As(2) bond length is 1.78 Å. In the second As site, As(2) is bonded in a distorted single-bond geometry to one Ca(1) and one As(1) atom.