The structure described by Na2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(6), one O(7), one O(9), two equivalent O(1), and two equivalent O(4) atoms. In the second Na site, Na(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), one O(7), and one O(9) atom. There are nine inequivalent O sites. In the first O site, O(7) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one O(6) atom. In the second O site, O(8) is bonded in a single-bond geometry to one O(3) atom. In the third O site, O(1) is bonded in a 4-coordinate geometry to one Na(2), two equivalent Na(1), and one O(2) atom. In the fourth O site, O(9) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one O(2), and one O(4) atom. In the fifth O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one O(1), and one O(9) atom. In the sixth O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one O(8) atom. In the seventh O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Na(1) and one O(9) atom. In the eighth O site, O(5) is bonded in a bent 120 degrees geometry to one Na(2) and one O(5) atom. In the ninth O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one O(7) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Na2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   11.260
_cell_length_b   5.203
_cell_length_c   12.776
_cell_angle_alpha   71.803
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   711.013
_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  0.116  0.819  0.599  1.0
  Na  Na1  1  0.616  0.181  0.901  1.0
  Na  Na2  1  0.884  0.181  0.401  1.0
  Na  Na3  1  0.384  0.819  0.099  1.0
  Na  Na4  1  0.676  0.879  0.670  1.0
  Na  Na5  1  0.176  0.121  0.830  1.0
  Na  Na6  1  0.324  0.121  0.330  1.0
  Na  Na7  1  0.824  0.879  0.170  1.0
  O  O8  1  0.920  0.969  0.598  1.0
  O  O9  1  0.420  0.031  0.902  1.0
  O  O10  1  0.080  0.031  0.402  1.0
  O  O11  1  0.580  0.969  0.098  1.0
  O  O12  1  0.414  0.015  0.802  1.0
  O  O13  1  0.914  0.985  0.698  1.0
  O  O14  1  0.586  0.985  0.198  1.0
  O  O15  1  0.086  0.015  0.302  1.0
  O  O16  1  0.768  0.747  0.880  1.0
  O  O17  1  0.268  0.253  0.620  1.0
  O  O18  1  0.232  0.253  0.120  1.0
  O  O19  1  0.732  0.747  0.380  1.0
  O  O20  1  0.049  0.321  0.572  1.0
  O  O21  1  0.549  0.679  0.928  1.0
  O  O22  1  0.951  0.679  0.428  1.0
  O  O23  1  0.451  0.321  0.072  1.0
  O  O24  1  0.443  0.998  0.504  1.0
  O  O25  1  0.943  0.002  0.996  1.0
  O  O26  1  0.557  0.002  0.496  1.0
  O  O27  1  0.057  0.998  0.004  1.0
  O  O28  1  0.213  0.693  0.804  1.0
  O  O29  1  0.713  0.307  0.696  1.0
  O  O30  1  0.787  0.307  0.196  1.0
  O  O31  1  0.287  0.693  0.304  1.0
  O  O32  1  0.611  0.434  0.682  1.0
  O  O33  1  0.111  0.566  0.818  1.0
  O  O34  1  0.389  0.566  0.318  1.0
  O  O35  1  0.889  0.434  0.182  1.0
  O  O36  1  0.867  0.668  0.922  1.0
  O  O37  1  0.367  0.332  0.578  1.0
  O  O38  1  0.133  0.332  0.078  1.0
  O  O39  1  0.633  0.668  0.422  1.0
  O  O40  1  0.523  0.702  0.827  1.0
  O  O41  1  0.023  0.298  0.673  1.0
  O  O42  1  0.477  0.298  0.173  1.0
  O  O43  1  0.977  0.702  0.327  1.0
[/CIF]
.
The structure described by Na2O9 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(6), one O(7), one O(9), two equivalent O(1), and two equivalent O(4) atoms. In the second Na site, Na(2) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), one O(7), and one O(9) atom. There are nine inequivalent O sites. In the first O site, O(7) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one O(6) atom. In the second O site, O(8) is bonded in a single-bond geometry to one O(3) atom. In the third O site, O(1) is bonded in a 4-coordinate geometry to one Na(2), two equivalent Na(1), and one O(2) atom. In the fourth O site, O(9) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one O(2), and one O(4) atom. In the fifth O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one O(1), and one O(9) atom. In the sixth O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one O(8) atom. In the seventh O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Na(1) and one O(9) atom. In the eighth O site, O(5) is bonded in a bent 120 degrees geometry to one Na(2) and one O(5) atom. In the ninth O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one O(7) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Na2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   11.260
_cell_length_b   5.203
_cell_length_c   12.776
_cell_angle_alpha   71.803
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   711.013
_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  0.116  0.819  0.599  1.0
  Na  Na1  1  0.616  0.181  0.901  1.0
  Na  Na2  1  0.884  0.181  0.401  1.0
  Na  Na3  1  0.384  0.819  0.099  1.0
  Na  Na4  1  0.676  0.879  0.670  1.0
  Na  Na5  1  0.176  0.121  0.830  1.0
  Na  Na6  1  0.324  0.121  0.330  1.0
  Na  Na7  1  0.824  0.879  0.170  1.0
  O  O8  1  0.920  0.969  0.598  1.0
  O  O9  1  0.420  0.031  0.902  1.0
  O  O10  1  0.080  0.031  0.402  1.0
  O  O11  1  0.580  0.969  0.098  1.0
  O  O12  1  0.414  0.015  0.802  1.0
  O  O13  1  0.914  0.985  0.698  1.0
  O  O14  1  0.586  0.985  0.198  1.0
  O  O15  1  0.086  0.015  0.302  1.0
  O  O16  1  0.768  0.747  0.880  1.0
  O  O17  1  0.268  0.253  0.620  1.0
  O  O18  1  0.232  0.253  0.120  1.0
  O  O19  1  0.732  0.747  0.380  1.0
  O  O20  1  0.049  0.321  0.572  1.0
  O  O21  1  0.549  0.679  0.928  1.0
  O  O22  1  0.951  0.679  0.428  1.0
  O  O23  1  0.451  0.321  0.072  1.0
  O  O24  1  0.443  0.998  0.504  1.0
  O  O25  1  0.943  0.002  0.996  1.0
  O  O26  1  0.557  0.002  0.496  1.0
  O  O27  1  0.057  0.998  0.004  1.0
  O  O28  1  0.213  0.693  0.804  1.0
  O  O29  1  0.713  0.307  0.696  1.0
  O  O30  1  0.787  0.307  0.196  1.0
  O  O31  1  0.287  0.693  0.304  1.0
  O  O32  1  0.611  0.434  0.682  1.0
  O  O33  1  0.111  0.566  0.818  1.0
  O  O34  1  0.389  0.566  0.318  1.0
  O  O35  1  0.889  0.434  0.182  1.0
  O  O36  1  0.867  0.668  0.922  1.0
  O  O37  1  0.367  0.332  0.578  1.0
  O  O38  1  0.133  0.332  0.078  1.0
  O  O39  1  0.633  0.668  0.422  1.0
  O  O40  1  0.523  0.702  0.827  1.0
  O  O41  1  0.023  0.298  0.673  1.0
  O  O42  1  0.477  0.298  0.173  1.0
  O  O43  1  0.977  0.702  0.327  1.0
[/CIF]
.