The material described by Na2Si2O5 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(1), one O(4), and three equivalent O(2) atoms to form distorted NaO5 trigonal bipyramids that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids, edges with two equivalent Na(2)O6 octahedra,  an edgeedge with one Si(2)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 28-72°. In the second Na site, Na(2) is bonded to one O(2), one O(3), one O(5), and three equivalent O(1) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 22°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  a cornercorner with one Na(1)O5 trigonal bipyramid, and edges with two equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 63-68°. In the second Si site, Si(2) is bonded to one O(2), one O(3), and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with three equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 44-52°. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Na(2) and two equivalent Si(1) atoms. In the second O site, O(1) is bonded in a 5-coordinate geometry to one Na(1), three equivalent Na(2), and one Si(1) atom. In the third O site, O(2) is bonded in a 5-coordinate geometry to one Na(2), three equivalent Na(1), and one Si(2) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Na(2), one Si(1), and one Si(2) atom. In the fifth O site, O(4) is bonded in a 3-coordinate geometry to one Na(1) and two equivalent Si(2) atoms. is represented by the CIF file [CIF]
data_Na2Si2O5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.830
_cell_length_b   8.106
_cell_length_c   12.192
_cell_angle_alpha   75.943
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   463.017
_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  0.755  0.622  0.444  1.0
  Na  Na1  1  0.255  0.378  0.056  1.0
  Na  Na2  1  0.245  0.378  0.556  1.0
  Na  Na3  1  0.745  0.622  0.944  1.0
  Na  Na4  1  0.225  0.862  0.472  1.0
  Na  Na5  1  0.725  0.138  0.028  1.0
  Na  Na6  1  0.775  0.138  0.528  1.0
  Na  Na7  1  0.275  0.862  0.972  1.0
  Si  Si8  1  0.183  0.973  0.181  1.0
  Si  Si9  1  0.683  0.027  0.319  1.0
  Si  Si10  1  0.817  0.027  0.819  1.0
  Si  Si11  1  0.317  0.973  0.681  1.0
  Si  Si12  1  0.298  0.598  0.277  1.0
  Si  Si13  1  0.798  0.402  0.223  1.0
  Si  Si14  1  0.702  0.402  0.723  1.0
  Si  Si15  1  0.202  0.598  0.777  1.0
  O  O16  1  0.255  0.095  0.561  1.0
  O  O17  1  0.755  0.905  0.939  1.0
  O  O18  1  0.745  0.905  0.439  1.0
  O  O19  1  0.245  0.095  0.061  1.0
  O  O20  1  0.267  0.611  0.902  1.0
  O  O21  1  0.767  0.389  0.598  1.0
  O  O22  1  0.733  0.389  0.098  1.0
  O  O23  1  0.233  0.611  0.402  1.0
  O  O24  1  0.253  0.775  0.679  1.0
  O  O25  1  0.753  0.225  0.821  1.0
  O  O26  1  0.747  0.225  0.321  1.0
  O  O27  1  0.247  0.775  0.179  1.0
  O  O28  1  0.873  0.549  0.768  1.0
  O  O29  1  0.373  0.451  0.732  1.0
  O  O30  1  0.127  0.451  0.232  1.0
  O  O31  1  0.627  0.549  0.268  1.0
  O  O32  1  0.855  0.984  0.214  1.0
  O  O33  1  0.355  0.016  0.286  1.0
  O  O34  1  0.145  0.016  0.786  1.0
  O  O35  1  0.645  0.984  0.714  1.0
[/CIF]
.
The material described by Na2Si2O5 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(1), one O(4), and three equivalent O(2) atoms to form distorted NaO5 trigonal bipyramids that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with three equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids, edges with two equivalent Na(2)O6 octahedra,  an edgeedge with one Si(2)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 28-72°. In the second Na site, Na(2) is bonded to one O(2), one O(3), one O(5), and three equivalent O(1) atoms to form distorted NaO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with two equivalent Na(1)O5 trigonal bipyramids, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Na(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 22°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), and two equivalent O(5) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(1)O4 tetrahedra,  a cornercorner with one Na(1)O5 trigonal bipyramid, and edges with two equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 63-68°. In the second Si site, Si(2) is bonded to one O(2), one O(3), and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, corners with three equivalent Na(1)O5 trigonal bipyramids, and  an edgeedge with one Na(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 44-52°. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one Na(2) and two equivalent Si(1) atoms. In the second O site, O(1) is bonded in a 5-coordinate geometry to one Na(1), three equivalent Na(2), and one Si(1) atom. In the third O site, O(2) is bonded in a 5-coordinate geometry to one Na(2), three equivalent Na(1), and one Si(2) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one Na(2), one Si(1), and one Si(2) atom. In the fifth O site, O(4) is bonded in a 3-coordinate geometry to one Na(1) and two equivalent Si(2) atoms. is represented by the CIF file [CIF]
data_Na2Si2O5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.830
_cell_length_b   8.106
_cell_length_c   12.192
_cell_angle_alpha   75.943
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   463.017
_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  0.755  0.622  0.444  1.0
  Na  Na1  1  0.255  0.378  0.056  1.0
  Na  Na2  1  0.245  0.378  0.556  1.0
  Na  Na3  1  0.745  0.622  0.944  1.0
  Na  Na4  1  0.225  0.862  0.472  1.0
  Na  Na5  1  0.725  0.138  0.028  1.0
  Na  Na6  1  0.775  0.138  0.528  1.0
  Na  Na7  1  0.275  0.862  0.972  1.0
  Si  Si8  1  0.183  0.973  0.181  1.0
  Si  Si9  1  0.683  0.027  0.319  1.0
  Si  Si10  1  0.817  0.027  0.819  1.0
  Si  Si11  1  0.317  0.973  0.681  1.0
  Si  Si12  1  0.298  0.598  0.277  1.0
  Si  Si13  1  0.798  0.402  0.223  1.0
  Si  Si14  1  0.702  0.402  0.723  1.0
  Si  Si15  1  0.202  0.598  0.777  1.0
  O  O16  1  0.255  0.095  0.561  1.0
  O  O17  1  0.755  0.905  0.939  1.0
  O  O18  1  0.745  0.905  0.439  1.0
  O  O19  1  0.245  0.095  0.061  1.0
  O  O20  1  0.267  0.611  0.902  1.0
  O  O21  1  0.767  0.389  0.598  1.0
  O  O22  1  0.733  0.389  0.098  1.0
  O  O23  1  0.233  0.611  0.402  1.0
  O  O24  1  0.253  0.775  0.679  1.0
  O  O25  1  0.753  0.225  0.821  1.0
  O  O26  1  0.747  0.225  0.321  1.0
  O  O27  1  0.247  0.775  0.179  1.0
  O  O28  1  0.873  0.549  0.768  1.0
  O  O29  1  0.373  0.451  0.732  1.0
  O  O30  1  0.127  0.451  0.232  1.0
  O  O31  1  0.627  0.549  0.268  1.0
  O  O32  1  0.855  0.984  0.214  1.0
  O  O33  1  0.355  0.016  0.286  1.0
  O  O34  1  0.145  0.016  0.786  1.0
  O  O35  1  0.645  0.984  0.714  1.0
[/CIF]
.