The material structure described by CaFeAs2O7 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a 6-coordinate geometry to one O(1), one O(5), one O(6), one O(7), and two equivalent O(3) atoms. Fe(1) is bonded to one O(1), one O(2), one O(5), one O(6), and one O(7) atom to form FeO5 square pyramids that share corners with two equivalent As(1)O4 tetrahedra and corners with three equivalent As(2)O4 tetrahedra. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(3), one O(4), and one O(6) atom to form AsO4 tetrahedra that share corners with two equivalent Fe(1)O5 square pyramids and  a cornercorner with one As(2)O4 tetrahedra. In the second As site, As(2) is bonded to one O(1), one O(4), one O(5), and one O(7) atom to form AsO4 tetrahedra that share corners with three equivalent Fe(1)O5 square pyramids and  a cornercorner with one As(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal planar geometry to one Ca(1), one Fe(1), and one As(2) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Ca(1), one Fe(1), and one As(1) atom. In the third O site, O(7) is bonded in a 3-coordinate geometry to one Ca(1), one Fe(1), and one As(2) atom. In the fourth O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one Fe(1), and one As(2) atom. In the fifth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Fe(1) and one As(1) atom. In the sixth O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one As(1) atom. In the seventh O site, O(4) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom. is represented by the CIF file [CIF]
data_CaFeAs2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.174
_cell_length_b   7.549
_cell_length_c   9.564
_cell_angle_alpha   68.830
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   617.682
_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
  Ca  Ca0  1  0.067  0.743  0.929  1.0
  Ca  Ca1  1  0.567  0.257  0.571  1.0
  Ca  Ca2  1  0.933  0.257  0.071  1.0
  Ca  Ca3  1  0.433  0.743  0.429  1.0
  Fe  Fe4  1  0.945  0.198  0.693  1.0
  Fe  Fe5  1  0.445  0.802  0.807  1.0
  Fe  Fe6  1  0.055  0.802  0.307  1.0
  Fe  Fe7  1  0.555  0.198  0.193  1.0
  As  As8  1  0.762  0.580  0.736  1.0
  As  As9  1  0.262  0.420  0.764  1.0
  As  As10  1  0.238  0.420  0.264  1.0
  As  As11  1  0.738  0.580  0.236  1.0
  As  As12  1  0.705  0.984  0.955  1.0
  As  As13  1  0.205  0.016  0.545  1.0
  As  As14  1  0.295  0.016  0.045  1.0
  As  As15  1  0.795  0.984  0.455  1.0
  O  O16  1  0.691  0.145  0.042  1.0
  O  O17  1  0.191  0.855  0.458  1.0
  O  O18  1  0.309  0.855  0.958  1.0
  O  O19  1  0.809  0.145  0.542  1.0
  O  O20  1  0.587  0.657  0.727  1.0
  O  O21  1  0.087  0.343  0.773  1.0
  O  O22  1  0.413  0.343  0.273  1.0
  O  O23  1  0.913  0.657  0.227  1.0
  O  O24  1  0.866  0.567  0.887  1.0
  O  O25  1  0.366  0.433  0.613  1.0
  O  O26  1  0.134  0.433  0.113  1.0
  O  O27  1  0.634  0.567  0.387  1.0
  O  O28  1  0.854  0.754  0.577  1.0
  O  O29  1  0.354  0.246  0.923  1.0
  O  O30  1  0.146  0.246  0.423  1.0
  O  O31  1  0.646  0.754  0.077  1.0
  O  O32  1  0.911  0.016  0.310  1.0
  O  O33  1  0.411  0.984  0.190  1.0
  O  O34  1  0.089  0.984  0.690  1.0
  O  O35  1  0.589  0.016  0.810  1.0
  O  O36  1  0.735  0.375  0.201  1.0
  O  O37  1  0.235  0.625  0.299  1.0
  O  O38  1  0.265  0.625  0.799  1.0
  O  O39  1  0.765  0.375  0.701  1.0
  O  O40  1  0.616  0.988  0.405  1.0
  O  O41  1  0.116  0.012  0.095  1.0
  O  O42  1  0.384  0.012  0.595  1.0
  O  O43  1  0.884  0.988  0.905  1.0
[/CIF]
.
The material structure described by CaFeAs2O7 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a 6-coordinate geometry to one O(1), one O(5), one O(6), one O(7), and two equivalent O(3) atoms. Fe(1) is bonded to one O(1), one O(2), one O(5), one O(6), and one O(7) atom to form FeO5 square pyramids that share corners with two equivalent As(1)O4 tetrahedra and corners with three equivalent As(2)O4 tetrahedra. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(2), one O(3), one O(4), and one O(6) atom to form AsO4 tetrahedra that share corners with two equivalent Fe(1)O5 square pyramids and  a cornercorner with one As(2)O4 tetrahedra. In the second As site, As(2) is bonded to one O(1), one O(4), one O(5), and one O(7) atom to form AsO4 tetrahedra that share corners with three equivalent Fe(1)O5 square pyramids and  a cornercorner with one As(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a distorted trigonal planar geometry to one Ca(1), one Fe(1), and one As(2) atom. In the second O site, O(6) is bonded in a distorted trigonal planar geometry to one Ca(1), one Fe(1), and one As(1) atom. In the third O site, O(7) is bonded in a 3-coordinate geometry to one Ca(1), one Fe(1), and one As(2) atom. In the fourth O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Ca(1), one Fe(1), and one As(2) atom. In the fifth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Fe(1) and one As(1) atom. In the sixth O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one As(1) atom. In the seventh O site, O(4) is bonded in a bent 120 degrees geometry to one As(1) and one As(2) atom. is represented by the CIF file [CIF]
data_CaFeAs2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.174
_cell_length_b   7.549
_cell_length_c   9.564
_cell_angle_alpha   68.830
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   617.682
_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
  Ca  Ca0  1  0.067  0.743  0.929  1.0
  Ca  Ca1  1  0.567  0.257  0.571  1.0
  Ca  Ca2  1  0.933  0.257  0.071  1.0
  Ca  Ca3  1  0.433  0.743  0.429  1.0
  Fe  Fe4  1  0.945  0.198  0.693  1.0
  Fe  Fe5  1  0.445  0.802  0.807  1.0
  Fe  Fe6  1  0.055  0.802  0.307  1.0
  Fe  Fe7  1  0.555  0.198  0.193  1.0
  As  As8  1  0.762  0.580  0.736  1.0
  As  As9  1  0.262  0.420  0.764  1.0
  As  As10  1  0.238  0.420  0.264  1.0
  As  As11  1  0.738  0.580  0.236  1.0
  As  As12  1  0.705  0.984  0.955  1.0
  As  As13  1  0.205  0.016  0.545  1.0
  As  As14  1  0.295  0.016  0.045  1.0
  As  As15  1  0.795  0.984  0.455  1.0
  O  O16  1  0.691  0.145  0.042  1.0
  O  O17  1  0.191  0.855  0.458  1.0
  O  O18  1  0.309  0.855  0.958  1.0
  O  O19  1  0.809  0.145  0.542  1.0
  O  O20  1  0.587  0.657  0.727  1.0
  O  O21  1  0.087  0.343  0.773  1.0
  O  O22  1  0.413  0.343  0.273  1.0
  O  O23  1  0.913  0.657  0.227  1.0
  O  O24  1  0.866  0.567  0.887  1.0
  O  O25  1  0.366  0.433  0.613  1.0
  O  O26  1  0.134  0.433  0.113  1.0
  O  O27  1  0.634  0.567  0.387  1.0
  O  O28  1  0.854  0.754  0.577  1.0
  O  O29  1  0.354  0.246  0.923  1.0
  O  O30  1  0.146  0.246  0.423  1.0
  O  O31  1  0.646  0.754  0.077  1.0
  O  O32  1  0.911  0.016  0.310  1.0
  O  O33  1  0.411  0.984  0.190  1.0
  O  O34  1  0.089  0.984  0.690  1.0
  O  O35  1  0.589  0.016  0.810  1.0
  O  O36  1  0.735  0.375  0.201  1.0
  O  O37  1  0.235  0.625  0.299  1.0
  O  O38  1  0.265  0.625  0.799  1.0
  O  O39  1  0.765  0.375  0.701  1.0
  O  O40  1  0.616  0.988  0.405  1.0
  O  O41  1  0.116  0.012  0.095  1.0
  O  O42  1  0.384  0.012  0.595  1.0
  O  O43  1  0.884  0.988  0.905  1.0
[/CIF]
.