The crystal structure described by Ca2Nb2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(12), one O(14), one O(2), one O(4), two equivalent O(7), and two equivalent O(9) atoms. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(11), one O(13), one O(8), two equivalent O(1), and two equivalent O(5) atoms. In the third Ca site, Ca(3) is bonded in a 8-coordinate geometry to one O(10), one O(14), one O(2), one O(3), one O(4), one O(6), one O(7), and one O(9) atom. In the fourth Ca site, Ca(4) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(3), one O(5), one O(6), one O(8), and two equivalent O(11) atoms. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(10), one O(12), one O(14), one O(4), and two equivalent O(9) atoms to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 23-45°. In the second Nb site, Nb(2) is bonded to one O(10), one O(11), one O(13), one O(14), one O(3), and one O(8) atom to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 29-45°. In the third Nb site, Nb(3) is bonded to one O(12), one O(2), one O(4), one O(6), and two equivalent O(7) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 23-42°. In the fourth Nb site, Nb(4) is bonded to one O(1), one O(13), one O(2), one O(3), one O(5), and one O(6) atom to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 29-42°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded to one Ca(4), two equivalent Ca(2), and one Nb(4) atom to form distorted OCa3Nb tetrahedra that share  a cornercorner with one O(2)Ca2Nb2 tetrahedra, corners with two equivalent O(1)Ca3Nb tetrahedra, corners with two equivalent O(11)Ca3Nb tetrahedra,  an edgeedge with one O(11)Ca3Nb tetrahedra, and edges with three equivalent O(5)Ca3Nb tetrahedra. In the second O site, O(2) is bonded to one Ca(1), one Ca(3), one Nb(3), and one Nb(4) atom to form distorted OCa2Nb2 tetrahedra that share  a cornercorner with one O(4)Ca2Nb2 tetrahedra,  a cornercorner with one O(1)Ca3Nb tetrahedra,  a cornercorner with one O(5)Ca3Nb tetrahedra, corners with two equivalent O(14)Ca2Nb2 tetrahedra, and  an edgeedge with one O(4)Ca2Nb2 tetrahedra. In the third O site, O(3) is bonded in a distorted see-saw-like geometry to one Ca(3), one Ca(4), one Nb(2), and one Nb(4) atom. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(3), one Nb(1), and one Nb(3) atom to form a mixture of corner and edge-sharing OCa2Nb2 tetrahedra. In the fifth O site, O(5) is bonded to one Ca(4), two equivalent Ca(2), and one Nb(4) atom to form distorted OCa3Nb tetrahedra that share  a cornercorner with one O(2)Ca2Nb2 tetrahedra, corners with two equivalent O(5)Ca3Nb tetrahedra, corners with four equivalent O(11)Ca3Nb tetrahedra, and edges with three equivalent O(1)Ca3Nb tetrahedra. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(3), one Ca(4), one Nb(3), and one Nb(4) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Ca(3), two equivalent Ca(1), and two equivalent Nb(3) atoms. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(4), and one Nb(2) atom. In the ninth O site, O(9) is bonded in a 5-coordinate geometry to one Ca(3), two equivalent Ca(1), and two equivalent Nb(1) atoms. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Ca(3), one Ca(4), one Nb(1), and one Nb(2) atom. In the eleventh O site, O(11) is bonded to one Ca(2), two equivalent Ca(4), and one Nb(2) atom to form distorted OCa3Nb tetrahedra that share  a cornercorner with one O(14)Ca2Nb2 tetrahedra, corners with two equivalent O(1)Ca3Nb tetrahedra, corners with two equivalent O(11)Ca3Nb tetrahedra, corners with four equivalent O(5)Ca3Nb tetrahedra, and  an edgeedge with one O(1)Ca3Nb tetrahedra. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to one Ca(1), one Nb(1), and one Nb(3) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Ca(2), one Nb(2), and one Nb(4) atom. In the fourteenth O site, O(14) is bonded to one Ca(1), one Ca(3), one Nb(1), and one Nb(2) atom to form distorted OCa2Nb2 tetrahedra that share  a cornercorner with one O(4)Ca2Nb2 tetrahedra,  a cornercorner with one O(11)Ca3Nb tetrahedra, corners with two equivalent O(2)Ca2Nb2 tetrahedra, and  an edgeedge with one O(4)Ca2Nb2 tetrahedra. is represented by the CIF card [CIF]
data_Ca2Nb2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.511
_cell_length_b   7.731
_cell_length_c   13.512
_cell_angle_alpha   81.677
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   569.606
_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  0.766  0.770  0.915  1.0
  Ca  Ca1  1  0.266  0.230  0.085  1.0
  Ca  Ca2  1  0.347  0.861  0.566  1.0
  Ca  Ca3  1  0.847  0.139  0.434  1.0
  Ca  Ca4  1  0.749  0.283  0.876  1.0
  Ca  Ca5  1  0.249  0.717  0.124  1.0
  Ca  Ca6  1  0.274  0.359  0.603  1.0
  Ca  Ca7  1  0.774  0.641  0.397  1.0
  Nb  Nb8  1  0.263  0.526  0.882  1.0
  Nb  Nb9  1  0.763  0.474  0.118  1.0
  Nb  Nb10  1  0.787  0.589  0.674  1.0
  Nb  Nb11  1  0.287  0.411  0.326  1.0
  Nb  Nb12  1  0.263  0.032  0.884  1.0
  Nb  Nb13  1  0.763  0.968  0.116  1.0
  Nb  Nb14  1  0.783  0.079  0.677  1.0
  Nb  Nb15  1  0.283  0.921  0.323  1.0
  O  O16  1  0.554  0.927  0.406  1.0
  O  O17  1  0.054  0.073  0.594  1.0
  O  O18  1  0.441  0.985  0.180  1.0
  O  O19  1  0.941  0.015  0.820  1.0
  O  O20  1  0.357  0.673  0.302  1.0
  O  O21  1  0.857  0.327  0.698  1.0
  O  O22  1  0.658  0.728  0.087  1.0
  O  O23  1  0.158  0.272  0.913  1.0
  O  O24  1  0.061  0.862  0.428  1.0
  O  O25  1  0.561  0.138  0.572  1.0
  O  O26  1  0.956  0.880  0.226  1.0
  O  O27  1  0.456  0.120  0.774  1.0
  O  O28  1  0.034  0.948  0.020  1.0
  O  O29  1  0.534  0.052  0.980  1.0
  O  O30  1  0.582  0.365  0.385  1.0
  O  O31  1  0.082  0.635  0.615  1.0
  O  O32  1  0.532  0.459  0.979  1.0
  O  O33  1  0.032  0.541  0.021  1.0
  O  O34  1  0.454  0.494  0.771  1.0
  O  O35  1  0.954  0.506  0.229  1.0
  O  O36  1  0.583  0.587  0.560  1.0
  O  O37  1  0.083  0.413  0.440  1.0
  O  O38  1  0.333  0.778  0.889  1.0
  O  O39  1  0.833  0.222  0.111  1.0
  O  O40  1  0.675  0.828  0.693  1.0
  O  O41  1  0.175  0.172  0.307  1.0
  O  O42  1  0.938  0.573  0.822  1.0
  O  O43  1  0.438  0.427  0.178  1.0
[/CIF]
.
The crystal structure described by Ca2Nb2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(12), one O(14), one O(2), one O(4), two equivalent O(7), and two equivalent O(9) atoms. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(11), one O(13), one O(8), two equivalent O(1), and two equivalent O(5) atoms. In the third Ca site, Ca(3) is bonded in a 8-coordinate geometry to one O(10), one O(14), one O(2), one O(3), one O(4), one O(6), one O(7), and one O(9) atom. In the fourth Ca site, Ca(4) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(3), one O(5), one O(6), one O(8), and two equivalent O(11) atoms. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(10), one O(12), one O(14), one O(4), and two equivalent O(9) atoms to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 23-45°. In the second Nb site, Nb(2) is bonded to one O(10), one O(11), one O(13), one O(14), one O(3), and one O(8) atom to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 29-45°. In the third Nb site, Nb(3) is bonded to one O(12), one O(2), one O(4), one O(6), and two equivalent O(7) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 23-42°. In the fourth Nb site, Nb(4) is bonded to one O(1), one O(13), one O(2), one O(3), one O(5), and one O(6) atom to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 29-42°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded to one Ca(4), two equivalent Ca(2), and one Nb(4) atom to form distorted OCa3Nb tetrahedra that share  a cornercorner with one O(2)Ca2Nb2 tetrahedra, corners with two equivalent O(1)Ca3Nb tetrahedra, corners with two equivalent O(11)Ca3Nb tetrahedra,  an edgeedge with one O(11)Ca3Nb tetrahedra, and edges with three equivalent O(5)Ca3Nb tetrahedra. In the second O site, O(2) is bonded to one Ca(1), one Ca(3), one Nb(3), and one Nb(4) atom to form distorted OCa2Nb2 tetrahedra that share  a cornercorner with one O(4)Ca2Nb2 tetrahedra,  a cornercorner with one O(1)Ca3Nb tetrahedra,  a cornercorner with one O(5)Ca3Nb tetrahedra, corners with two equivalent O(14)Ca2Nb2 tetrahedra, and  an edgeedge with one O(4)Ca2Nb2 tetrahedra. In the third O site, O(3) is bonded in a distorted see-saw-like geometry to one Ca(3), one Ca(4), one Nb(2), and one Nb(4) atom. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(3), one Nb(1), and one Nb(3) atom to form a mixture of corner and edge-sharing OCa2Nb2 tetrahedra. In the fifth O site, O(5) is bonded to one Ca(4), two equivalent Ca(2), and one Nb(4) atom to form distorted OCa3Nb tetrahedra that share  a cornercorner with one O(2)Ca2Nb2 tetrahedra, corners with two equivalent O(5)Ca3Nb tetrahedra, corners with four equivalent O(11)Ca3Nb tetrahedra, and edges with three equivalent O(1)Ca3Nb tetrahedra. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(3), one Ca(4), one Nb(3), and one Nb(4) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Ca(3), two equivalent Ca(1), and two equivalent Nb(3) atoms. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Ca(2), one Ca(4), and one Nb(2) atom. In the ninth O site, O(9) is bonded in a 5-coordinate geometry to one Ca(3), two equivalent Ca(1), and two equivalent Nb(1) atoms. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Ca(3), one Ca(4), one Nb(1), and one Nb(2) atom. In the eleventh O site, O(11) is bonded to one Ca(2), two equivalent Ca(4), and one Nb(2) atom to form distorted OCa3Nb tetrahedra that share  a cornercorner with one O(14)Ca2Nb2 tetrahedra, corners with two equivalent O(1)Ca3Nb tetrahedra, corners with two equivalent O(11)Ca3Nb tetrahedra, corners with four equivalent O(5)Ca3Nb tetrahedra, and  an edgeedge with one O(1)Ca3Nb tetrahedra. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to one Ca(1), one Nb(1), and one Nb(3) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Ca(2), one Nb(2), and one Nb(4) atom. In the fourteenth O site, O(14) is bonded to one Ca(1), one Ca(3), one Nb(1), and one Nb(2) atom to form distorted OCa2Nb2 tetrahedra that share  a cornercorner with one O(4)Ca2Nb2 tetrahedra,  a cornercorner with one O(11)Ca3Nb tetrahedra, corners with two equivalent O(2)Ca2Nb2 tetrahedra, and  an edgeedge with one O(4)Ca2Nb2 tetrahedra. is represented by the CIF card [CIF]
data_Ca2Nb2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.511
_cell_length_b   7.731
_cell_length_c   13.512
_cell_angle_alpha   81.677
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   569.606
_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  0.766  0.770  0.915  1.0
  Ca  Ca1  1  0.266  0.230  0.085  1.0
  Ca  Ca2  1  0.347  0.861  0.566  1.0
  Ca  Ca3  1  0.847  0.139  0.434  1.0
  Ca  Ca4  1  0.749  0.283  0.876  1.0
  Ca  Ca5  1  0.249  0.717  0.124  1.0
  Ca  Ca6  1  0.274  0.359  0.603  1.0
  Ca  Ca7  1  0.774  0.641  0.397  1.0
  Nb  Nb8  1  0.263  0.526  0.882  1.0
  Nb  Nb9  1  0.763  0.474  0.118  1.0
  Nb  Nb10  1  0.787  0.589  0.674  1.0
  Nb  Nb11  1  0.287  0.411  0.326  1.0
  Nb  Nb12  1  0.263  0.032  0.884  1.0
  Nb  Nb13  1  0.763  0.968  0.116  1.0
  Nb  Nb14  1  0.783  0.079  0.677  1.0
  Nb  Nb15  1  0.283  0.921  0.323  1.0
  O  O16  1  0.554  0.927  0.406  1.0
  O  O17  1  0.054  0.073  0.594  1.0
  O  O18  1  0.441  0.985  0.180  1.0
  O  O19  1  0.941  0.015  0.820  1.0
  O  O20  1  0.357  0.673  0.302  1.0
  O  O21  1  0.857  0.327  0.698  1.0
  O  O22  1  0.658  0.728  0.087  1.0
  O  O23  1  0.158  0.272  0.913  1.0
  O  O24  1  0.061  0.862  0.428  1.0
  O  O25  1  0.561  0.138  0.572  1.0
  O  O26  1  0.956  0.880  0.226  1.0
  O  O27  1  0.456  0.120  0.774  1.0
  O  O28  1  0.034  0.948  0.020  1.0
  O  O29  1  0.534  0.052  0.980  1.0
  O  O30  1  0.582  0.365  0.385  1.0
  O  O31  1  0.082  0.635  0.615  1.0
  O  O32  1  0.532  0.459  0.979  1.0
  O  O33  1  0.032  0.541  0.021  1.0
  O  O34  1  0.454  0.494  0.771  1.0
  O  O35  1  0.954  0.506  0.229  1.0
  O  O36  1  0.583  0.587  0.560  1.0
  O  O37  1  0.083  0.413  0.440  1.0
  O  O38  1  0.333  0.778  0.889  1.0
  O  O39  1  0.833  0.222  0.111  1.0
  O  O40  1  0.675  0.828  0.693  1.0
  O  O41  1  0.175  0.172  0.307  1.0
  O  O42  1  0.938  0.573  0.822  1.0
  O  O43  1  0.438  0.427  0.178  1.0
[/CIF]
.