The crystal structure described by K2CaP2O7 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(1), one O(4), two equivalent O(6), two equivalent O(7), and three equivalent O(3) atoms. In the second K site, K(2) is bonded in a 9-coordinate geometry to one O(1), one O(4), one O(6), one O(7), two equivalent O(2), and three equivalent O(5) atoms. Ca(1) is bonded to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form CaO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 8-46°. In the second P site, P(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 16-41°. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ca(1), and one P(1) atom. In the second O site, O(1) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Ca(1), and one P(2) atom. In the third O site, O(2) is bonded in a distorted bent 120 degrees geometry to two equivalent K(2), one P(1), and one P(2) atom. In the fourth O site, O(3) is bonded in a 5-coordinate geometry to three equivalent K(1), one Ca(1), and one P(2) atom. In the fifth O site, O(4) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Ca(1), and one P(2) atom. In the sixth O site, O(5) is bonded in a 2-coordinate geometry to three equivalent K(2), one Ca(1), and one P(1) atom. In the seventh O site, O(6) is bonded in a 1-coordinate geometry to one K(2), two equivalent K(1), one Ca(1), and one P(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_K2CaP2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.745
_cell_length_b   9.932
_cell_length_c   14.433
_cell_angle_alpha   62.373
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   729.713
_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  0.731  0.466  0.178  1.0
  K  K1  1  0.238  0.987  0.140  1.0
  K  K2  1  0.769  0.466  0.678  1.0
  K  K3  1  0.269  0.534  0.822  1.0
  K  K4  1  0.262  0.987  0.640  1.0
  K  K5  1  0.762  0.013  0.860  1.0
  K  K6  1  0.738  0.013  0.360  1.0
  K  K7  1  0.231  0.534  0.322  1.0
  Ca  Ca8  1  0.238  0.733  0.518  1.0
  Ca  Ca9  1  0.262  0.733  0.018  1.0
  Ca  Ca10  1  0.762  0.267  0.482  1.0
  Ca  Ca11  1  0.738  0.267  0.982  1.0
  P  P12  1  0.755  0.828  0.641  1.0
  P  P13  1  0.255  0.172  0.859  1.0
  P  P14  1  0.780  0.679  0.874  1.0
  P  P15  1  0.720  0.679  0.374  1.0
  P  P16  1  0.280  0.321  0.626  1.0
  P  P17  1  0.220  0.321  0.126  1.0
  P  P18  1  0.745  0.828  0.141  1.0
  P  P19  1  0.245  0.172  0.359  1.0
  O  O20  1  0.603  0.697  0.946  1.0
  O  O21  1  0.704  0.817  0.758  1.0
  O  O22  1  0.262  0.470  0.632  1.0
  O  O23  1  0.103  0.303  0.554  1.0
  O  O24  1  0.796  0.817  0.258  1.0
  O  O25  1  0.971  0.281  0.109  1.0
  O  O26  1  0.204  0.183  0.742  1.0
  O  O27  1  0.237  0.000  0.430  1.0
  O  O28  1  0.738  0.530  0.368  1.0
  O  O29  1  0.455  0.249  0.379  1.0
  O  O30  1  0.737  1.000  0.070  1.0
  O  O31  1  0.029  0.719  0.891  1.0
  O  O32  1  0.897  0.697  0.446  1.0
  O  O33  1  0.545  0.751  0.621  1.0
  O  O34  1  0.012  0.251  0.352  1.0
  O  O35  1  0.488  0.251  0.852  1.0
  O  O36  1  0.045  0.249  0.879  1.0
  O  O37  1  0.988  0.749  0.648  1.0
  O  O38  1  0.296  0.183  0.242  1.0
  O  O39  1  0.512  0.749  0.148  1.0
  O  O40  1  0.529  0.281  0.609  1.0
  O  O41  1  0.397  0.303  0.054  1.0
  O  O42  1  0.471  0.719  0.391  1.0
  O  O43  1  0.762  0.530  0.868  1.0
  O  O44  1  0.263  0.000  0.930  1.0
  O  O45  1  0.763  1.000  0.570  1.0
  O  O46  1  0.238  0.470  0.132  1.0
  O  O47  1  0.955  0.751  0.121  1.0
[/CIF]
.
The crystal structure described by K2CaP2O7 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(1), one O(4), two equivalent O(6), two equivalent O(7), and three equivalent O(3) atoms. In the second K site, K(2) is bonded in a 9-coordinate geometry to one O(1), one O(4), one O(6), one O(7), two equivalent O(2), and three equivalent O(5) atoms. Ca(1) is bonded to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form CaO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra and corners with three equivalent P(2)O4 tetrahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(2), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one P(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 8-46°. In the second P site, P(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Ca(1)O6 octahedra and  a cornercorner with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 16-41°. There are seven inequivalent O sites. In the first O site, O(7) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Ca(1), and one P(1) atom. In the second O site, O(1) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Ca(1), and one P(2) atom. In the third O site, O(2) is bonded in a distorted bent 120 degrees geometry to two equivalent K(2), one P(1), and one P(2) atom. In the fourth O site, O(3) is bonded in a 5-coordinate geometry to three equivalent K(1), one Ca(1), and one P(2) atom. In the fifth O site, O(4) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Ca(1), and one P(2) atom. In the sixth O site, O(5) is bonded in a 2-coordinate geometry to three equivalent K(2), one Ca(1), and one P(1) atom. In the seventh O site, O(6) is bonded in a 1-coordinate geometry to one K(2), two equivalent K(1), one Ca(1), and one P(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_K2CaP2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.745
_cell_length_b   9.932
_cell_length_c   14.433
_cell_angle_alpha   62.373
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   729.713
_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  0.731  0.466  0.178  1.0
  K  K1  1  0.238  0.987  0.140  1.0
  K  K2  1  0.769  0.466  0.678  1.0
  K  K3  1  0.269  0.534  0.822  1.0
  K  K4  1  0.262  0.987  0.640  1.0
  K  K5  1  0.762  0.013  0.860  1.0
  K  K6  1  0.738  0.013  0.360  1.0
  K  K7  1  0.231  0.534  0.322  1.0
  Ca  Ca8  1  0.238  0.733  0.518  1.0
  Ca  Ca9  1  0.262  0.733  0.018  1.0
  Ca  Ca10  1  0.762  0.267  0.482  1.0
  Ca  Ca11  1  0.738  0.267  0.982  1.0
  P  P12  1  0.755  0.828  0.641  1.0
  P  P13  1  0.255  0.172  0.859  1.0
  P  P14  1  0.780  0.679  0.874  1.0
  P  P15  1  0.720  0.679  0.374  1.0
  P  P16  1  0.280  0.321  0.626  1.0
  P  P17  1  0.220  0.321  0.126  1.0
  P  P18  1  0.745  0.828  0.141  1.0
  P  P19  1  0.245  0.172  0.359  1.0
  O  O20  1  0.603  0.697  0.946  1.0
  O  O21  1  0.704  0.817  0.758  1.0
  O  O22  1  0.262  0.470  0.632  1.0
  O  O23  1  0.103  0.303  0.554  1.0
  O  O24  1  0.796  0.817  0.258  1.0
  O  O25  1  0.971  0.281  0.109  1.0
  O  O26  1  0.204  0.183  0.742  1.0
  O  O27  1  0.237  0.000  0.430  1.0
  O  O28  1  0.738  0.530  0.368  1.0
  O  O29  1  0.455  0.249  0.379  1.0
  O  O30  1  0.737  1.000  0.070  1.0
  O  O31  1  0.029  0.719  0.891  1.0
  O  O32  1  0.897  0.697  0.446  1.0
  O  O33  1  0.545  0.751  0.621  1.0
  O  O34  1  0.012  0.251  0.352  1.0
  O  O35  1  0.488  0.251  0.852  1.0
  O  O36  1  0.045  0.249  0.879  1.0
  O  O37  1  0.988  0.749  0.648  1.0
  O  O38  1  0.296  0.183  0.242  1.0
  O  O39  1  0.512  0.749  0.148  1.0
  O  O40  1  0.529  0.281  0.609  1.0
  O  O41  1  0.397  0.303  0.054  1.0
  O  O42  1  0.471  0.719  0.391  1.0
  O  O43  1  0.762  0.530  0.868  1.0
  O  O44  1  0.263  0.000  0.930  1.0
  O  O45  1  0.763  1.000  0.570  1.0
  O  O46  1  0.238  0.470  0.132  1.0
  O  O47  1  0.955  0.751  0.121  1.0
[/CIF]
.