The compound described by Na2P2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(2), one O(5), one O(6), and two equivalent O(3) atoms to form NaO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one Na(1)O5 square pyramid. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. There are two inequivalent P sites. In the first P site, P(1) 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 Na(1)O5 square pyramids and  a cornercorner with one P(2)O4 tetrahedra. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids and  a cornercorner with one P(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one P(2) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one P(2) atom. In the third O site, O(7) is bonded in a bent 150 degrees geometry to one Na(2) and one P(2) atom. In the fourth O site, O(1) is bonded in a bent 150 degrees geometry to one Na(2) and one P(1) atom. In the fifth O site, O(2) is bonded in a distorted linear geometry to one Na(1) and one P(1) atom. In the sixth O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), two equivalent Na(1), and one P(1) atom. In the seventh O site, O(4) is bonded in a 3-coordinate geometry to one Na(2), one P(1), and one P(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Na2P2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.664
_cell_length_b   7.042
_cell_length_c   7.158
_cell_angle_alpha   82.132
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   682.287
_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
  Na  Na0  1  0.898  0.543  0.849  1.0
  Na  Na1  1  0.398  0.957  0.151  1.0
  Na  Na2  1  0.102  0.457  0.151  1.0
  Na  Na3  1  0.602  0.043  0.849  1.0
  Na  Na4  1  0.871  0.160  0.226  1.0
  Na  Na5  1  0.371  0.340  0.774  1.0
  Na  Na6  1  0.129  0.840  0.774  1.0
  Na  Na7  1  0.629  0.660  0.226  1.0
  P  P8  1  0.895  0.659  0.313  1.0
  P  P9  1  0.395  0.841  0.687  1.0
  P  P10  1  0.105  0.341  0.687  1.0
  P  P11  1  0.605  0.159  0.313  1.0
  P  P12  1  0.923  0.079  0.751  1.0
  P  P13  1  0.423  0.421  0.249  1.0
  P  P14  1  0.077  0.921  0.249  1.0
  P  P15  1  0.577  0.579  0.751  1.0
  O  O16  1  0.792  0.740  0.273  1.0
  O  O17  1  0.292  0.760  0.727  1.0
  O  O18  1  0.208  0.260  0.727  1.0
  O  O19  1  0.708  0.240  0.273  1.0
  O  O20  1  0.898  0.582  0.522  1.0
  O  O21  1  0.398  0.918  0.478  1.0
  O  O22  1  0.102  0.418  0.478  1.0
  O  O23  1  0.602  0.082  0.522  1.0
  O  O24  1  0.927  0.517  0.183  1.0
  O  O25  1  0.427  0.983  0.817  1.0
  O  O26  1  0.073  0.483  0.817  1.0
  O  O27  1  0.573  0.017  0.183  1.0
  O  O28  1  0.963  0.849  0.274  1.0
  O  O29  1  0.463  0.651  0.726  1.0
  O  O30  1  0.037  0.151  0.726  1.0
  O  O31  1  0.537  0.349  0.274  1.0
  O  O32  1  0.937  0.867  0.824  1.0
  O  O33  1  0.437  0.633  0.176  1.0
  O  O34  1  0.063  0.133  0.176  1.0
  O  O35  1  0.563  0.367  0.824  1.0
  O  O36  1  0.871  0.196  0.882  1.0
  O  O37  1  0.371  0.304  0.118  1.0
  O  O38  1  0.129  0.804  0.118  1.0
  O  O39  1  0.629  0.696  0.882  1.0
  O  O40  1  0.876  0.093  0.556  1.0
  O  O41  1  0.376  0.407  0.444  1.0
  O  O42  1  0.124  0.907  0.444  1.0
  O  O43  1  0.624  0.593  0.556  1.0
[/CIF]
.
The compound described by Na2P2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(2), one O(5), one O(6), and two equivalent O(3) atoms to form NaO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one Na(1)O5 square pyramid. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. There are two inequivalent P sites. In the first P site, P(1) 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 Na(1)O5 square pyramids and  a cornercorner with one P(2)O4 tetrahedra. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids and  a cornercorner with one P(1)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one P(2) atom. In the second O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one P(2) atom. In the third O site, O(7) is bonded in a bent 150 degrees geometry to one Na(2) and one P(2) atom. In the fourth O site, O(1) is bonded in a bent 150 degrees geometry to one Na(2) and one P(1) atom. In the fifth O site, O(2) is bonded in a distorted linear geometry to one Na(1) and one P(1) atom. In the sixth O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), two equivalent Na(1), and one P(1) atom. In the seventh O site, O(4) is bonded in a 3-coordinate geometry to one Na(2), one P(1), and one P(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Na2P2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.664
_cell_length_b   7.042
_cell_length_c   7.158
_cell_angle_alpha   82.132
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   682.287
_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
  Na  Na0  1  0.898  0.543  0.849  1.0
  Na  Na1  1  0.398  0.957  0.151  1.0
  Na  Na2  1  0.102  0.457  0.151  1.0
  Na  Na3  1  0.602  0.043  0.849  1.0
  Na  Na4  1  0.871  0.160  0.226  1.0
  Na  Na5  1  0.371  0.340  0.774  1.0
  Na  Na6  1  0.129  0.840  0.774  1.0
  Na  Na7  1  0.629  0.660  0.226  1.0
  P  P8  1  0.895  0.659  0.313  1.0
  P  P9  1  0.395  0.841  0.687  1.0
  P  P10  1  0.105  0.341  0.687  1.0
  P  P11  1  0.605  0.159  0.313  1.0
  P  P12  1  0.923  0.079  0.751  1.0
  P  P13  1  0.423  0.421  0.249  1.0
  P  P14  1  0.077  0.921  0.249  1.0
  P  P15  1  0.577  0.579  0.751  1.0
  O  O16  1  0.792  0.740  0.273  1.0
  O  O17  1  0.292  0.760  0.727  1.0
  O  O18  1  0.208  0.260  0.727  1.0
  O  O19  1  0.708  0.240  0.273  1.0
  O  O20  1  0.898  0.582  0.522  1.0
  O  O21  1  0.398  0.918  0.478  1.0
  O  O22  1  0.102  0.418  0.478  1.0
  O  O23  1  0.602  0.082  0.522  1.0
  O  O24  1  0.927  0.517  0.183  1.0
  O  O25  1  0.427  0.983  0.817  1.0
  O  O26  1  0.073  0.483  0.817  1.0
  O  O27  1  0.573  0.017  0.183  1.0
  O  O28  1  0.963  0.849  0.274  1.0
  O  O29  1  0.463  0.651  0.726  1.0
  O  O30  1  0.037  0.151  0.726  1.0
  O  O31  1  0.537  0.349  0.274  1.0
  O  O32  1  0.937  0.867  0.824  1.0
  O  O33  1  0.437  0.633  0.176  1.0
  O  O34  1  0.063  0.133  0.176  1.0
  O  O35  1  0.563  0.367  0.824  1.0
  O  O36  1  0.871  0.196  0.882  1.0
  O  O37  1  0.371  0.304  0.118  1.0
  O  O38  1  0.129  0.804  0.118  1.0
  O  O39  1  0.629  0.696  0.882  1.0
  O  O40  1  0.876  0.093  0.556  1.0
  O  O41  1  0.376  0.407  0.444  1.0
  O  O42  1  0.124  0.907  0.444  1.0
  O  O43  1  0.624  0.593  0.556  1.0
[/CIF]
.