The crystal structure described by Na2Si2O5 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form distorted NaO5 square pyramids that share corners with four equivalent Na(1)O5 square pyramids, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(2), one O(5), two equivalent O(3), and two equivalent O(4) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Na(1)O5 square pyramid. In the second Si site, Si(2) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Na(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(2) and two equivalent Si(2) atoms. In the third O site, O(3) is bonded to two equivalent Na(1), two equivalent Na(2), and one Si(2) atom to form distorted corner-sharing ONa4Si trigonal bipyramids. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to two equivalent Na(1), two equivalent Na(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Na(2), one Si(1), and one Si(2) atom. is represented by the CIF card [CIF]
data_Na2Si2O5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.802
_cell_length_b   8.119
_cell_length_c   11.832
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   461.281
_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  0.571  0.435  0.273  1.0
  Na  Na1  1  0.098  0.689  0.192  1.0
  Na  Na2  1  0.071  0.065  0.773  1.0
  Na  Na3  1  0.098  0.189  0.308  1.0
  Na  Na4  1  0.071  0.565  0.727  1.0
  Na  Na5  1  0.571  0.935  0.227  1.0
  Na  Na6  1  0.598  0.811  0.692  1.0
  Na  Na7  1  0.598  0.311  0.808  1.0
  Si  Si8  1  0.522  0.948  0.932  1.0
  Si  Si9  1  0.022  0.552  0.432  1.0
  Si  Si10  1  0.522  0.448  0.568  1.0
  Si  Si11  1  0.642  0.109  0.475  1.0
  Si  Si12  1  0.142  0.391  0.975  1.0
  Si  Si13  1  0.142  0.891  0.525  1.0
  Si  Si14  1  0.022  0.052  0.068  1.0
  Si  Si15  1  0.642  0.609  0.025  1.0
  O  O16  1  0.190  0.971  0.961  1.0
  O  O17  1  0.973  0.058  0.486  1.0
  O  O18  1  0.579  0.666  0.151  1.0
  O  O19  1  0.079  0.834  0.651  1.0
  O  O20  1  0.079  0.334  0.849  1.0
  O  O21  1  0.588  0.029  0.813  1.0
  O  O22  1  0.084  0.251  0.072  1.0
  O  O23  1  0.690  0.529  0.461  1.0
  O  O24  1  0.473  0.442  0.986  1.0
  O  O25  1  0.088  0.471  0.313  1.0
  O  O26  1  0.584  0.749  0.928  1.0
  O  O27  1  0.973  0.558  0.014  1.0
  O  O28  1  0.690  0.029  0.039  1.0
  O  O29  1  0.084  0.751  0.428  1.0
  O  O30  1  0.473  0.942  0.514  1.0
  O  O31  1  0.588  0.529  0.687  1.0
  O  O32  1  0.584  0.249  0.572  1.0
  O  O33  1  0.088  0.971  0.187  1.0
  O  O34  1  0.579  0.166  0.349  1.0
  O  O35  1  0.190  0.471  0.539  1.0
[/CIF]
.
The crystal structure described by Na2Si2O5 crystallizes in the orthorhombic Pna2_1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(1), two equivalent O(3), and two equivalent O(4) atoms to form distorted NaO5 square pyramids that share corners with four equivalent Na(1)O5 square pyramids, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Si(1)O4 tetrahedra. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(2), one O(5), two equivalent O(3), and two equivalent O(4) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Na(1)O5 square pyramid. In the second Si site, Si(2) is bonded to one O(3), one O(5), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(1)O5 square pyramids,  a cornercorner with one Si(1)O4 tetrahedra, and corners with two equivalent Si(2)O4 tetrahedra. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Na(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(2) and two equivalent Si(2) atoms. In the third O site, O(3) is bonded to two equivalent Na(1), two equivalent Na(2), and one Si(2) atom to form distorted corner-sharing ONa4Si trigonal bipyramids. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to two equivalent Na(1), two equivalent Na(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to one Na(2), one Si(1), and one Si(2) atom. is represented by the CIF card [CIF]
data_Na2Si2O5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.802
_cell_length_b   8.119
_cell_length_c   11.832
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   461.281
_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  0.571  0.435  0.273  1.0
  Na  Na1  1  0.098  0.689  0.192  1.0
  Na  Na2  1  0.071  0.065  0.773  1.0
  Na  Na3  1  0.098  0.189  0.308  1.0
  Na  Na4  1  0.071  0.565  0.727  1.0
  Na  Na5  1  0.571  0.935  0.227  1.0
  Na  Na6  1  0.598  0.811  0.692  1.0
  Na  Na7  1  0.598  0.311  0.808  1.0
  Si  Si8  1  0.522  0.948  0.932  1.0
  Si  Si9  1  0.022  0.552  0.432  1.0
  Si  Si10  1  0.522  0.448  0.568  1.0
  Si  Si11  1  0.642  0.109  0.475  1.0
  Si  Si12  1  0.142  0.391  0.975  1.0
  Si  Si13  1  0.142  0.891  0.525  1.0
  Si  Si14  1  0.022  0.052  0.068  1.0
  Si  Si15  1  0.642  0.609  0.025  1.0
  O  O16  1  0.190  0.971  0.961  1.0
  O  O17  1  0.973  0.058  0.486  1.0
  O  O18  1  0.579  0.666  0.151  1.0
  O  O19  1  0.079  0.834  0.651  1.0
  O  O20  1  0.079  0.334  0.849  1.0
  O  O21  1  0.588  0.029  0.813  1.0
  O  O22  1  0.084  0.251  0.072  1.0
  O  O23  1  0.690  0.529  0.461  1.0
  O  O24  1  0.473  0.442  0.986  1.0
  O  O25  1  0.088  0.471  0.313  1.0
  O  O26  1  0.584  0.749  0.928  1.0
  O  O27  1  0.973  0.558  0.014  1.0
  O  O28  1  0.690  0.029  0.039  1.0
  O  O29  1  0.084  0.751  0.428  1.0
  O  O30  1  0.473  0.942  0.514  1.0
  O  O31  1  0.588  0.529  0.687  1.0
  O  O32  1  0.584  0.249  0.572  1.0
  O  O33  1  0.088  0.971  0.187  1.0
  O  O34  1  0.579  0.166  0.349  1.0
  O  O35  1  0.190  0.471  0.539  1.0
[/CIF]
.