The material structure described by Na2Cr3O9 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(4), one O(6), and four equivalent O(2) atoms. In the second Na site, Na(2) is bonded to one O(5), one O(7), two equivalent O(1), and two equivalent O(2) atoms to form distorted NaO6 octahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with three equivalent Cr(2)O4 tetrahedra, and corners with three equivalent Cr(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 60°. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form CrO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Cr(2)O4 tetrahedra, corners with two equivalent Cr(3)O4 tetrahedra, and edges with two equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles are 60°. In the second Cr site, Cr(2) is bonded to one O(5), one O(6), and two equivalent O(1) atoms to form CrO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra and corners with three equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-69°. In the third Cr site, Cr(3) is bonded to one O(3), one O(7), and two equivalent O(2) atoms to form CrO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra and corners with three equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-67°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Na(2), one Cr(1), and one Cr(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(2), two equivalent Na(1), and one Cr(3) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Cr(3) and two equivalent Cr(1) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to one Na(1) and two equivalent Cr(1) atoms. In the fifth O site, O(5) is bonded in a distorted water-like geometry to one Na(2) and one Cr(2) atom. In the sixth O site, O(6) is bonded in a distorted linear geometry to one Na(1) and one Cr(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Na(2) and one Cr(3) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Na2Cr3O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.935
_cell_length_b   7.838
_cell_length_c   8.603
_cell_angle_alpha   110.942
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   373.748
_cell_formula_units_Z   2
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  0.750  0.159  0.094  1.0
  Na  Na1  1  0.250  0.841  0.906  1.0
  Na  Na2  1  0.750  0.781  0.247  1.0
  Na  Na3  1  0.250  0.219  0.753  1.0
  Cr  Cr4  1  0.500  0.500  0.500  1.0
  Cr  Cr5  1  0.000  0.500  0.500  1.0
  Cr  Cr6  1  0.250  0.495  0.166  1.0
  Cr  Cr7  1  0.750  0.505  0.834  1.0
  Cr  Cr8  1  0.250  0.068  0.322  1.0
  Cr  Cr9  1  0.750  0.932  0.678  1.0
  O  O10  1  0.481  0.557  0.295  1.0
  O  O11  1  0.981  0.443  0.705  1.0
  O  O12  1  0.519  0.443  0.705  1.0
  O  O13  1  0.019  0.557  0.295  1.0
  O  O14  1  0.476  0.999  0.205  1.0
  O  O15  1  0.976  0.001  0.795  1.0
  O  O16  1  0.524  0.001  0.795  1.0
  O  O17  1  0.024  0.999  0.205  1.0
  O  O18  1  0.250  0.313  0.419  1.0
  O  O19  1  0.750  0.687  0.581  1.0
  O  O20  1  0.750  0.352  0.410  1.0
  O  O21  1  0.250  0.648  0.590  1.0
  O  O22  1  0.250  0.276  0.059  1.0
  O  O23  1  0.750  0.724  0.941  1.0
  O  O24  1  0.250  0.608  0.041  1.0
  O  O25  1  0.750  0.392  0.959  1.0
  O  O26  1  0.250  0.982  0.467  1.0
  O  O27  1  0.750  0.018  0.533  1.0
[/CIF]
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The material structure described by Na2Cr3O9 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(4), one O(6), and four equivalent O(2) atoms. In the second Na site, Na(2) is bonded to one O(5), one O(7), two equivalent O(1), and two equivalent O(2) atoms to form distorted NaO6 octahedra that share corners with two equivalent Cr(1)O6 octahedra, corners with three equivalent Cr(2)O4 tetrahedra, and corners with three equivalent Cr(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 60°. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form CrO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Cr(2)O4 tetrahedra, corners with two equivalent Cr(3)O4 tetrahedra, and edges with two equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles are 60°. In the second Cr site, Cr(2) is bonded to one O(5), one O(6), and two equivalent O(1) atoms to form CrO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra and corners with three equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-69°. In the third Cr site, Cr(3) is bonded to one O(3), one O(7), and two equivalent O(2) atoms to form CrO4 tetrahedra that share corners with two equivalent Cr(1)O6 octahedra and corners with three equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-67°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Na(2), one Cr(1), and one Cr(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(2), two equivalent Na(1), and one Cr(3) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Cr(3) and two equivalent Cr(1) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal non-coplanar geometry to one Na(1) and two equivalent Cr(1) atoms. In the fifth O site, O(5) is bonded in a distorted water-like geometry to one Na(2) and one Cr(2) atom. In the sixth O site, O(6) is bonded in a distorted linear geometry to one Na(1) and one Cr(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 120 degrees geometry to one Na(2) and one Cr(3) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Na2Cr3O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.935
_cell_length_b   7.838
_cell_length_c   8.603
_cell_angle_alpha   110.942
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   373.748
_cell_formula_units_Z   2
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  0.750  0.159  0.094  1.0
  Na  Na1  1  0.250  0.841  0.906  1.0
  Na  Na2  1  0.750  0.781  0.247  1.0
  Na  Na3  1  0.250  0.219  0.753  1.0
  Cr  Cr4  1  0.500  0.500  0.500  1.0
  Cr  Cr5  1  0.000  0.500  0.500  1.0
  Cr  Cr6  1  0.250  0.495  0.166  1.0
  Cr  Cr7  1  0.750  0.505  0.834  1.0
  Cr  Cr8  1  0.250  0.068  0.322  1.0
  Cr  Cr9  1  0.750  0.932  0.678  1.0
  O  O10  1  0.481  0.557  0.295  1.0
  O  O11  1  0.981  0.443  0.705  1.0
  O  O12  1  0.519  0.443  0.705  1.0
  O  O13  1  0.019  0.557  0.295  1.0
  O  O14  1  0.476  0.999  0.205  1.0
  O  O15  1  0.976  0.001  0.795  1.0
  O  O16  1  0.524  0.001  0.795  1.0
  O  O17  1  0.024  0.999  0.205  1.0
  O  O18  1  0.250  0.313  0.419  1.0
  O  O19  1  0.750  0.687  0.581  1.0
  O  O20  1  0.750  0.352  0.410  1.0
  O  O21  1  0.250  0.648  0.590  1.0
  O  O22  1  0.250  0.276  0.059  1.0
  O  O23  1  0.750  0.724  0.941  1.0
  O  O24  1  0.250  0.608  0.041  1.0
  O  O25  1  0.750  0.392  0.959  1.0
  O  O26  1  0.250  0.982  0.467  1.0
  O  O27  1  0.750  0.018  0.533  1.0
[/CIF]
.