The structure described by KFeAs2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 10-coordinate geometry to one O(11), one O(12), one O(2), one O(3), one O(4), one O(5), one O(6), one O(9), and two equivalent O(14) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(1), one O(11), one O(12), one O(6), one O(7), and two equivalent O(10) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(12), one O(14), one O(3), one O(4), one O(6), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one As(1)O4 tetrahedra,  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra, and corners with two equivalent As(4)O4 tetrahedra. In the second Fe site, Fe(2) is bonded to one O(1), one O(10), one O(11), one O(2), one O(5), and one O(7) atom to form FeO6 octahedra that share  a cornercorner with one As(2)O4 tetrahedra,  a cornercorner with one As(4)O4 tetrahedra, corners with two equivalent As(1)O4 tetrahedra, and corners with two equivalent As(3)O4 tetrahedra. There are four inequivalent As sites. In the first As site, As(1) is bonded to one O(10), one O(13), one O(2), and one O(6) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one As(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-55°. In the second As site, As(2) is bonded to one O(12), one O(4), one O(7), and one O(9) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one As(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-57°. In the third As site, As(3) is bonded to one O(1), one O(13), one O(3), and one O(5) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 31-53°. In the fourth As site, As(4) is bonded to one O(11), one O(14), one O(8), and one O(9) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-52°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one K(2), one Fe(2), and one As(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one Fe(2), and one As(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one K(1), one Fe(1), and one As(3) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one K(1), one Fe(1), and one As(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one K(1), one Fe(2), and one As(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Fe(1), and one As(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one K(2), one Fe(2), and one As(2) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(4) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one K(1), one As(2), and one As(4) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to two equivalent K(2), one Fe(2), and one As(1) atom. In the eleventh O site, O(11) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Fe(2), and one As(4) atom. In the twelfth O site, O(12) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Fe(1), and one As(2) atom. In the thirteenth O site, O(13) is bonded in a bent 120 degrees geometry to one As(1) and one As(3) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to two equivalent K(1), one Fe(1), and one As(4) atom. is represented by the CIF card [CIF]
data_KFeAs2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.830
_cell_length_b   8.583
_cell_length_c   10.309
_cell_angle_alpha   89.807
_cell_angle_beta   89.601
_cell_angle_gamma   73.361
_symmetry_Int_Tables_number   1
_cell_volume   663.798
_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
  K  K0  1  0.164  0.460  0.676  1.0
  K  K1  1  0.824  0.061  0.175  1.0
  K  K2  1  0.836  0.540  0.324  1.0
  K  K3  1  0.176  0.939  0.825  1.0
  Fe  Fe4  1  0.766  0.264  0.595  1.0
  Fe  Fe5  1  0.234  0.736  0.405  1.0
  Fe  Fe6  1  0.765  0.770  0.901  1.0
  Fe  Fe7  1  0.235  0.230  0.099  1.0
  As  As8  1  0.124  0.665  0.103  1.0
  As  As9  1  0.559  0.680  0.645  1.0
  As  As10  1  0.446  0.797  0.130  1.0
  As  As11  1  0.876  0.335  0.897  1.0
  As  As12  1  0.848  0.849  0.580  1.0
  As  As13  1  0.441  0.320  0.355  1.0
  As  As14  1  0.554  0.203  0.870  1.0
  As  As15  1  0.152  0.151  0.420  1.0
  O  O16  1  0.327  0.982  0.074  1.0
  O  O17  1  0.108  0.474  0.121  1.0
  O  O18  1  0.446  0.757  0.293  1.0
  O  O19  1  0.282  0.500  0.374  1.0
  O  O20  1  0.892  0.526  0.879  1.0
  O  O21  1  0.663  0.738  0.078  1.0
  O  O22  1  0.080  0.778  0.242  1.0
  O  O23  1  0.454  0.241  0.201  1.0
  O  O24  1  0.184  0.958  0.472  1.0
  O  O25  1  0.718  0.500  0.626  1.0
  O  O26  1  0.363  0.185  0.457  1.0
  O  O27  1  0.637  0.815  0.543  1.0
  O  O28  1  0.991  0.783  0.988  1.0
  O  O29  1  0.102  0.192  0.261  1.0
  O  O30  1  0.816  0.042  0.528  1.0
  O  O31  1  0.354  0.681  0.591  1.0
  O  O32  1  0.654  0.344  0.949  1.0
  O  O33  1  0.337  0.262  0.922  1.0
  O  O34  1  0.920  0.222  0.758  1.0
  O  O35  1  0.646  0.319  0.409  1.0
  O  O36  1  0.346  0.656  0.051  1.0
  O  O37  1  0.554  0.243  0.707  1.0
  O  O38  1  0.002  0.711  0.490  1.0
  O  O39  1  0.009  0.217  0.012  1.0
  O  O40  1  0.898  0.808  0.739  1.0
  O  O41  1  0.546  0.759  0.799  1.0
  O  O42  1  0.673  0.018  0.926  1.0
  O  O43  1  0.998  0.289  0.510  1.0
[/CIF]
.
The structure described by KFeAs2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 10-coordinate geometry to one O(11), one O(12), one O(2), one O(3), one O(4), one O(5), one O(6), one O(9), and two equivalent O(14) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(1), one O(11), one O(12), one O(6), one O(7), and two equivalent O(10) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(12), one O(14), one O(3), one O(4), one O(6), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one As(1)O4 tetrahedra,  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra, and corners with two equivalent As(4)O4 tetrahedra. In the second Fe site, Fe(2) is bonded to one O(1), one O(10), one O(11), one O(2), one O(5), and one O(7) atom to form FeO6 octahedra that share  a cornercorner with one As(2)O4 tetrahedra,  a cornercorner with one As(4)O4 tetrahedra, corners with two equivalent As(1)O4 tetrahedra, and corners with two equivalent As(3)O4 tetrahedra. There are four inequivalent As sites. In the first As site, As(1) is bonded to one O(10), one O(13), one O(2), and one O(6) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one As(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-55°. In the second As site, As(2) is bonded to one O(12), one O(4), one O(7), and one O(9) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one As(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-57°. In the third As site, As(3) is bonded to one O(1), one O(13), one O(3), and one O(5) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 31-53°. In the fourth As site, As(4) is bonded to one O(11), one O(14), one O(8), and one O(9) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-52°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one K(2), one Fe(2), and one As(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one Fe(2), and one As(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one K(1), one Fe(1), and one As(3) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one K(1), one Fe(1), and one As(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one K(1), one Fe(2), and one As(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Fe(1), and one As(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one K(2), one Fe(2), and one As(2) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(4) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one K(1), one As(2), and one As(4) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to two equivalent K(2), one Fe(2), and one As(1) atom. In the eleventh O site, O(11) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Fe(2), and one As(4) atom. In the twelfth O site, O(12) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Fe(1), and one As(2) atom. In the thirteenth O site, O(13) is bonded in a bent 120 degrees geometry to one As(1) and one As(3) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to two equivalent K(1), one Fe(1), and one As(4) atom. is represented by the CIF card [CIF]
data_KFeAs2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.830
_cell_length_b   8.583
_cell_length_c   10.309
_cell_angle_alpha   89.807
_cell_angle_beta   89.601
_cell_angle_gamma   73.361
_symmetry_Int_Tables_number   1
_cell_volume   663.798
_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
  K  K0  1  0.164  0.460  0.676  1.0
  K  K1  1  0.824  0.061  0.175  1.0
  K  K2  1  0.836  0.540  0.324  1.0
  K  K3  1  0.176  0.939  0.825  1.0
  Fe  Fe4  1  0.766  0.264  0.595  1.0
  Fe  Fe5  1  0.234  0.736  0.405  1.0
  Fe  Fe6  1  0.765  0.770  0.901  1.0
  Fe  Fe7  1  0.235  0.230  0.099  1.0
  As  As8  1  0.124  0.665  0.103  1.0
  As  As9  1  0.559  0.680  0.645  1.0
  As  As10  1  0.446  0.797  0.130  1.0
  As  As11  1  0.876  0.335  0.897  1.0
  As  As12  1  0.848  0.849  0.580  1.0
  As  As13  1  0.441  0.320  0.355  1.0
  As  As14  1  0.554  0.203  0.870  1.0
  As  As15  1  0.152  0.151  0.420  1.0
  O  O16  1  0.327  0.982  0.074  1.0
  O  O17  1  0.108  0.474  0.121  1.0
  O  O18  1  0.446  0.757  0.293  1.0
  O  O19  1  0.282  0.500  0.374  1.0
  O  O20  1  0.892  0.526  0.879  1.0
  O  O21  1  0.663  0.738  0.078  1.0
  O  O22  1  0.080  0.778  0.242  1.0
  O  O23  1  0.454  0.241  0.201  1.0
  O  O24  1  0.184  0.958  0.472  1.0
  O  O25  1  0.718  0.500  0.626  1.0
  O  O26  1  0.363  0.185  0.457  1.0
  O  O27  1  0.637  0.815  0.543  1.0
  O  O28  1  0.991  0.783  0.988  1.0
  O  O29  1  0.102  0.192  0.261  1.0
  O  O30  1  0.816  0.042  0.528  1.0
  O  O31  1  0.354  0.681  0.591  1.0
  O  O32  1  0.654  0.344  0.949  1.0
  O  O33  1  0.337  0.262  0.922  1.0
  O  O34  1  0.920  0.222  0.758  1.0
  O  O35  1  0.646  0.319  0.409  1.0
  O  O36  1  0.346  0.656  0.051  1.0
  O  O37  1  0.554  0.243  0.707  1.0
  O  O38  1  0.002  0.711  0.490  1.0
  O  O39  1  0.009  0.217  0.012  1.0
  O  O40  1  0.898  0.808  0.739  1.0
  O  O41  1  0.546  0.759  0.799  1.0
  O  O42  1  0.673  0.018  0.926  1.0
  O  O43  1  0.998  0.289  0.510  1.0
[/CIF]
.