The material structure described by K2CaAs2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to one O(3), one O(5), two equivalent O(1), two equivalent O(7), and three equivalent O(2) atoms. In the second K site, K(2) is bonded in a 9-coordinate geometry to one O(1), one O(3), one O(5), one O(7), two equivalent O(6), and three equivalent O(4) atoms. Ca(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(7) atom to form CaO6 octahedra that share corners with three 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(5), and one O(6) atom to form AsO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 30-50°. In the second As site, As(2) is bonded to one O(1), one O(4), one O(6), and one O(7) atom to form AsO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 19-51°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ca(1), and one As(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to three equivalent K(1), one Ca(1), and one As(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Ca(1), and one As(1) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to three equivalent K(2), one Ca(1), and one As(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Ca(1), and one As(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to two equivalent K(2), one As(1), and one As(2) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ca(1), and one As(2) atom. is represented by the CIF card [CIF]
data_K2CaAs2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.932
_cell_length_b   9.371
_cell_length_c   14.919
_cell_angle_alpha   74.064
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   797.421
_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  0.233  0.466  0.336  1.0
  K  K1  1  0.754  0.967  0.114  1.0
  K  K2  1  0.246  0.033  0.886  1.0
  K  K3  1  0.733  0.534  0.164  1.0
  K  K4  1  0.267  0.466  0.836  1.0
  K  K5  1  0.254  0.033  0.386  1.0
  K  K6  1  0.746  0.967  0.614  1.0
  K  K7  1  0.767  0.534  0.664  1.0
  Ca  Ca8  1  0.272  0.266  0.137  1.0
  Ca  Ca9  1  0.728  0.734  0.863  1.0
  Ca  Ca10  1  0.772  0.734  0.363  1.0
  Ca  Ca11  1  0.228  0.266  0.637  1.0
  As  As12  1  0.707  0.315  0.472  1.0
  As  As13  1  0.260  0.824  0.198  1.0
  As  As14  1  0.293  0.685  0.528  1.0
  As  As15  1  0.740  0.176  0.802  1.0
  As  As16  1  0.240  0.824  0.698  1.0
  As  As17  1  0.760  0.176  0.302  1.0
  As  As18  1  0.793  0.315  0.972  1.0
  As  As19  1  0.207  0.685  0.028  1.0
  O  O20  1  0.989  0.273  0.249  1.0
  O  O21  1  0.511  0.273  0.749  1.0
  O  O22  1  0.248  0.525  0.612  1.0
  O  O23  1  0.252  0.525  0.112  1.0
  O  O24  1  0.430  0.275  0.499  1.0
  O  O25  1  0.266  0.007  0.194  1.0
  O  O26  1  0.130  0.715  0.431  1.0
  O  O27  1  0.930  0.725  0.001  1.0
  O  O28  1  0.801  0.163  0.426  1.0
  O  O29  1  0.011  0.727  0.751  1.0
  O  O30  1  0.008  0.739  0.229  1.0
  O  O31  1  0.570  0.725  0.501  1.0
  O  O32  1  0.992  0.261  0.771  1.0
  O  O33  1  0.748  0.475  0.888  1.0
  O  O34  1  0.870  0.285  0.569  1.0
  O  O35  1  0.234  0.007  0.694  1.0
  O  O36  1  0.070  0.275  0.999  1.0
  O  O37  1  0.489  0.727  0.251  1.0
  O  O38  1  0.492  0.739  0.729  1.0
  O  O39  1  0.508  0.261  0.271  1.0
  O  O40  1  0.766  0.993  0.306  1.0
  O  O41  1  0.734  0.993  0.806  1.0
  O  O42  1  0.199  0.837  0.574  1.0
  O  O43  1  0.370  0.715  0.931  1.0
  O  O44  1  0.301  0.837  0.074  1.0
  O  O45  1  0.699  0.163  0.926  1.0
  O  O46  1  0.630  0.285  0.069  1.0
  O  O47  1  0.752  0.475  0.388  1.0
[/CIF]
.
The material structure described by K2CaAs2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to one O(3), one O(5), two equivalent O(1), two equivalent O(7), and three equivalent O(2) atoms. In the second K site, K(2) is bonded in a 9-coordinate geometry to one O(1), one O(3), one O(5), one O(7), two equivalent O(6), and three equivalent O(4) atoms. Ca(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(7) atom to form CaO6 octahedra that share corners with three 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(5), and one O(6) atom to form AsO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 30-50°. In the second As site, As(2) is bonded to one O(1), one O(4), one O(6), and one O(7) atom to form AsO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 19-51°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ca(1), and one As(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to three equivalent K(1), one Ca(1), and one As(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Ca(1), and one As(1) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to three equivalent K(2), one Ca(1), and one As(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Ca(1), and one As(1) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to two equivalent K(2), one As(1), and one As(2) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ca(1), and one As(2) atom. is represented by the CIF card [CIF]
data_K2CaAs2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.932
_cell_length_b   9.371
_cell_length_c   14.919
_cell_angle_alpha   74.064
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   797.421
_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  0.233  0.466  0.336  1.0
  K  K1  1  0.754  0.967  0.114  1.0
  K  K2  1  0.246  0.033  0.886  1.0
  K  K3  1  0.733  0.534  0.164  1.0
  K  K4  1  0.267  0.466  0.836  1.0
  K  K5  1  0.254  0.033  0.386  1.0
  K  K6  1  0.746  0.967  0.614  1.0
  K  K7  1  0.767  0.534  0.664  1.0
  Ca  Ca8  1  0.272  0.266  0.137  1.0
  Ca  Ca9  1  0.728  0.734  0.863  1.0
  Ca  Ca10  1  0.772  0.734  0.363  1.0
  Ca  Ca11  1  0.228  0.266  0.637  1.0
  As  As12  1  0.707  0.315  0.472  1.0
  As  As13  1  0.260  0.824  0.198  1.0
  As  As14  1  0.293  0.685  0.528  1.0
  As  As15  1  0.740  0.176  0.802  1.0
  As  As16  1  0.240  0.824  0.698  1.0
  As  As17  1  0.760  0.176  0.302  1.0
  As  As18  1  0.793  0.315  0.972  1.0
  As  As19  1  0.207  0.685  0.028  1.0
  O  O20  1  0.989  0.273  0.249  1.0
  O  O21  1  0.511  0.273  0.749  1.0
  O  O22  1  0.248  0.525  0.612  1.0
  O  O23  1  0.252  0.525  0.112  1.0
  O  O24  1  0.430  0.275  0.499  1.0
  O  O25  1  0.266  0.007  0.194  1.0
  O  O26  1  0.130  0.715  0.431  1.0
  O  O27  1  0.930  0.725  0.001  1.0
  O  O28  1  0.801  0.163  0.426  1.0
  O  O29  1  0.011  0.727  0.751  1.0
  O  O30  1  0.008  0.739  0.229  1.0
  O  O31  1  0.570  0.725  0.501  1.0
  O  O32  1  0.992  0.261  0.771  1.0
  O  O33  1  0.748  0.475  0.888  1.0
  O  O34  1  0.870  0.285  0.569  1.0
  O  O35  1  0.234  0.007  0.694  1.0
  O  O36  1  0.070  0.275  0.999  1.0
  O  O37  1  0.489  0.727  0.251  1.0
  O  O38  1  0.492  0.739  0.729  1.0
  O  O39  1  0.508  0.261  0.271  1.0
  O  O40  1  0.766  0.993  0.306  1.0
  O  O41  1  0.734  0.993  0.806  1.0
  O  O42  1  0.199  0.837  0.574  1.0
  O  O43  1  0.370  0.715  0.931  1.0
  O  O44  1  0.301  0.837  0.074  1.0
  O  O45  1  0.699  0.163  0.926  1.0
  O  O46  1  0.630  0.285  0.069  1.0
  O  O47  1  0.752  0.475  0.388  1.0
[/CIF]
.