The structure described by Na2Cr2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(11), one O(12), one O(13), one O(2), and one O(8) atom. In the second Na site, Na(2) is bonded to one O(10), one O(3), one O(4), one O(6), one O(7), and one O(8) atom to form NaO6 octahedra that share  a cornercorner with one Na(3)O6 octahedra,  a cornercorner with one Cr(3)O4 tetrahedra,  a cornercorner with one Cr(4)O4 tetrahedra, corners with two equivalent Cr(1)O4 tetrahedra, corners with two equivalent Cr(2)O4 tetrahedra,  an edgeedge with one Na(3)O6 octahedra, and  an edgeedge with one Na(4)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 72°. In the third Na site, Na(3) is bonded to one O(10), one O(11), one O(14), one O(3), one O(4), and one O(9) atom to form NaO6 octahedra that share  a cornercorner with one Na(2)O6 octahedra,  a cornercorner with one Cr(2)O4 tetrahedra,  a cornercorner with one Cr(3)O4 tetrahedra, corners with two equivalent Cr(1)O4 tetrahedra, corners with two equivalent Cr(4)O4 tetrahedra,  an edgeedge with one Na(2)O6 octahedra, and  an edgeedge with one Na(4)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 72°. In the fourth Na site, Na(4) is bonded to one O(1), one O(12), one O(13), one O(14), one O(6), one O(7), and one O(9) atom to form distorted NaO7 pentagonal bipyramids that share  a cornercorner with one Cr(2)O4 tetrahedra, corners with two equivalent Cr(1)O4 tetrahedra, corners with two equivalent Cr(3)O4 tetrahedra, corners with two equivalent Cr(4)O4 tetrahedra,  an edgeedge with one Na(2)O6 octahedra, and  an edgeedge with one Na(3)O6 octahedra. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(14), one O(2), one O(3), and one O(7) atom to form CrO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Na(3)O6 octahedra, corners with two equivalent Na(4)O7 pentagonal bipyramids, and  a cornercorner with one Cr(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-64°. In the second Cr site, Cr(2) is bonded to one O(10), one O(13), one O(2), and one O(8) atom to form CrO4 tetrahedra that share  a cornercorner with one Na(3)O6 octahedra, corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Na(4)O7 pentagonal bipyramid, and  a cornercorner with one Cr(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-59°. In the third Cr site, Cr(3) is bonded to one O(1), one O(11), one O(5), and one O(6) atom to form CrO4 tetrahedra that share  a cornercorner with one Na(2)O6 octahedra,  a cornercorner with one Na(3)O6 octahedra, corners with two equivalent Na(4)O7 pentagonal bipyramids, and  a cornercorner with one Cr(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 42-66°. In the fourth Cr site, Cr(4) is bonded to one O(12), one O(4), one O(5), and one O(9) atom to form CrO4 tetrahedra that share  a cornercorner with one Na(2)O6 octahedra, corners with two equivalent Na(3)O6 octahedra, corners with two equivalent Na(4)O7 pentagonal bipyramids, and  a cornercorner with one Cr(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-66°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Na(1), one Na(4), and one Cr(3) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Na(1), one Cr(1), and one Cr(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Na(2), one Na(3), and one Cr(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Na(2), one Na(3), and one Cr(4) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Cr(3) and one Cr(4) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Na(2), one Na(4), and one Cr(3) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Na(2), one Na(4), and one Cr(1) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one Cr(2) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Na(3), one Na(4), and one Cr(4) atom. In the tenth O site, O(10) is bonded in a distorted trigonal planar geometry to one Na(2), one Na(3), and one Cr(2) atom. In the eleventh O site, O(11) is bonded in a trigonal planar geometry to one Na(1), one Na(3), and one Cr(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal non-coplanar geometry to one Na(1), one Na(4), and one Cr(4) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Na(1), one Na(4), and one Cr(2) atom. In the fourteenth O site, O(14) is bonded in a 3-coordinate geometry to one Na(3), one Na(4), and one Cr(1) atom. is represented by the CIF file [CIF]
data_Na2Cr2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.655
_cell_length_b   9.234
_cell_length_c   9.883
_cell_angle_alpha   76.034
_cell_angle_beta   70.881
_cell_angle_gamma   70.470
_symmetry_Int_Tables_number   1
_cell_volume   615.246
_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  0.530  0.607  0.222  1.0
  Na  Na1  1  0.031  0.267  0.355  1.0
  Na  Na2  1  0.025  0.099  0.738  1.0
  Na  Na3  1  0.975  0.901  0.262  1.0
  Na  Na4  1  0.531  0.213  0.179  1.0
  Na  Na5  1  0.470  0.393  0.778  1.0
  Na  Na6  1  0.969  0.733  0.645  1.0
  Na  Na7  1  0.469  0.787  0.821  1.0
  Cr  Cr8  1  0.322  0.911  0.446  1.0
  Cr  Cr9  1  0.298  0.373  0.533  1.0
  Cr  Cr10  1  0.702  0.627  0.467  1.0
  Cr  Cr11  1  0.170  0.590  0.082  1.0
  Cr  Cr12  1  0.678  0.089  0.554  1.0
  Cr  Cr13  1  0.830  0.410  0.918  1.0
  Cr  Cr14  1  0.793  0.845  0.010  1.0
  Cr  Cr15  1  0.207  0.155  0.990  1.0
  O  O16  1  0.298  0.593  0.915  1.0
  O  O17  1  0.463  0.230  0.621  1.0
  O  O18  1  0.144  0.864  0.432  1.0
  O  O19  1  0.910  0.878  0.842  1.0
  O  O20  1  0.076  0.332  0.908  1.0
  O  O21  1  0.795  0.586  0.836  1.0
  O  O22  1  0.330  0.079  0.351  1.0
  O  O23  1  0.856  0.136  0.568  1.0
  O  O24  1  0.924  0.668  0.092  1.0
  O  O25  1  0.757  0.474  0.392  1.0
  O  O26  1  0.773  0.982  0.095  1.0
  O  O27  1  0.227  0.018  0.905  1.0
  O  O28  1  0.889  0.686  0.440  1.0
  O  O29  1  0.205  0.414  0.164  1.0
  O  O30  1  0.233  0.695  0.159  1.0
  O  O31  1  0.702  0.407  0.085  1.0
  O  O32  1  0.586  0.823  0.026  1.0
  O  O33  1  0.598  0.596  0.637  1.0
  O  O34  1  0.767  0.305  0.841  1.0
  O  O35  1  0.670  0.921  0.649  1.0
  O  O36  1  0.706  0.083  0.386  1.0
  O  O37  1  0.537  0.770  0.379  1.0
  O  O38  1  0.402  0.404  0.363  1.0
  O  O39  1  0.414  0.177  0.974  1.0
  O  O40  1  0.111  0.314  0.560  1.0
  O  O41  1  0.294  0.917  0.614  1.0
  O  O42  1  0.090  0.122  0.158  1.0
  O  O43  1  0.243  0.526  0.608  1.0
[/CIF]
.
The structure described by Na2Cr2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(11), one O(12), one O(13), one O(2), and one O(8) atom. In the second Na site, Na(2) is bonded to one O(10), one O(3), one O(4), one O(6), one O(7), and one O(8) atom to form NaO6 octahedra that share  a cornercorner with one Na(3)O6 octahedra,  a cornercorner with one Cr(3)O4 tetrahedra,  a cornercorner with one Cr(4)O4 tetrahedra, corners with two equivalent Cr(1)O4 tetrahedra, corners with two equivalent Cr(2)O4 tetrahedra,  an edgeedge with one Na(3)O6 octahedra, and  an edgeedge with one Na(4)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 72°. In the third Na site, Na(3) is bonded to one O(10), one O(11), one O(14), one O(3), one O(4), and one O(9) atom to form NaO6 octahedra that share  a cornercorner with one Na(2)O6 octahedra,  a cornercorner with one Cr(2)O4 tetrahedra,  a cornercorner with one Cr(3)O4 tetrahedra, corners with two equivalent Cr(1)O4 tetrahedra, corners with two equivalent Cr(4)O4 tetrahedra,  an edgeedge with one Na(2)O6 octahedra, and  an edgeedge with one Na(4)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 72°. In the fourth Na site, Na(4) is bonded to one O(1), one O(12), one O(13), one O(14), one O(6), one O(7), and one O(9) atom to form distorted NaO7 pentagonal bipyramids that share  a cornercorner with one Cr(2)O4 tetrahedra, corners with two equivalent Cr(1)O4 tetrahedra, corners with two equivalent Cr(3)O4 tetrahedra, corners with two equivalent Cr(4)O4 tetrahedra,  an edgeedge with one Na(2)O6 octahedra, and  an edgeedge with one Na(3)O6 octahedra. There are four inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(14), one O(2), one O(3), and one O(7) atom to form CrO4 tetrahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Na(3)O6 octahedra, corners with two equivalent Na(4)O7 pentagonal bipyramids, and  a cornercorner with one Cr(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 41-64°. In the second Cr site, Cr(2) is bonded to one O(10), one O(13), one O(2), and one O(8) atom to form CrO4 tetrahedra that share  a cornercorner with one Na(3)O6 octahedra, corners with two equivalent Na(2)O6 octahedra,  a cornercorner with one Na(4)O7 pentagonal bipyramid, and  a cornercorner with one Cr(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-59°. In the third Cr site, Cr(3) is bonded to one O(1), one O(11), one O(5), and one O(6) atom to form CrO4 tetrahedra that share  a cornercorner with one Na(2)O6 octahedra,  a cornercorner with one Na(3)O6 octahedra, corners with two equivalent Na(4)O7 pentagonal bipyramids, and  a cornercorner with one Cr(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 42-66°. In the fourth Cr site, Cr(4) is bonded to one O(12), one O(4), one O(5), and one O(9) atom to form CrO4 tetrahedra that share  a cornercorner with one Na(2)O6 octahedra, corners with two equivalent Na(3)O6 octahedra, corners with two equivalent Na(4)O7 pentagonal bipyramids, and  a cornercorner with one Cr(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-66°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Na(1), one Na(4), and one Cr(3) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Na(1), one Cr(1), and one Cr(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Na(2), one Na(3), and one Cr(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Na(2), one Na(3), and one Cr(4) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one Cr(3) and one Cr(4) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Na(2), one Na(4), and one Cr(3) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Na(2), one Na(4), and one Cr(1) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one Cr(2) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Na(3), one Na(4), and one Cr(4) atom. In the tenth O site, O(10) is bonded in a distorted trigonal planar geometry to one Na(2), one Na(3), and one Cr(2) atom. In the eleventh O site, O(11) is bonded in a trigonal planar geometry to one Na(1), one Na(3), and one Cr(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal non-coplanar geometry to one Na(1), one Na(4), and one Cr(4) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Na(1), one Na(4), and one Cr(2) atom. In the fourteenth O site, O(14) is bonded in a 3-coordinate geometry to one Na(3), one Na(4), and one Cr(1) atom. is represented by the CIF file [CIF]
data_Na2Cr2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.655
_cell_length_b   9.234
_cell_length_c   9.883
_cell_angle_alpha   76.034
_cell_angle_beta   70.881
_cell_angle_gamma   70.470
_symmetry_Int_Tables_number   1
_cell_volume   615.246
_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  0.530  0.607  0.222  1.0
  Na  Na1  1  0.031  0.267  0.355  1.0
  Na  Na2  1  0.025  0.099  0.738  1.0
  Na  Na3  1  0.975  0.901  0.262  1.0
  Na  Na4  1  0.531  0.213  0.179  1.0
  Na  Na5  1  0.470  0.393  0.778  1.0
  Na  Na6  1  0.969  0.733  0.645  1.0
  Na  Na7  1  0.469  0.787  0.821  1.0
  Cr  Cr8  1  0.322  0.911  0.446  1.0
  Cr  Cr9  1  0.298  0.373  0.533  1.0
  Cr  Cr10  1  0.702  0.627  0.467  1.0
  Cr  Cr11  1  0.170  0.590  0.082  1.0
  Cr  Cr12  1  0.678  0.089  0.554  1.0
  Cr  Cr13  1  0.830  0.410  0.918  1.0
  Cr  Cr14  1  0.793  0.845  0.010  1.0
  Cr  Cr15  1  0.207  0.155  0.990  1.0
  O  O16  1  0.298  0.593  0.915  1.0
  O  O17  1  0.463  0.230  0.621  1.0
  O  O18  1  0.144  0.864  0.432  1.0
  O  O19  1  0.910  0.878  0.842  1.0
  O  O20  1  0.076  0.332  0.908  1.0
  O  O21  1  0.795  0.586  0.836  1.0
  O  O22  1  0.330  0.079  0.351  1.0
  O  O23  1  0.856  0.136  0.568  1.0
  O  O24  1  0.924  0.668  0.092  1.0
  O  O25  1  0.757  0.474  0.392  1.0
  O  O26  1  0.773  0.982  0.095  1.0
  O  O27  1  0.227  0.018  0.905  1.0
  O  O28  1  0.889  0.686  0.440  1.0
  O  O29  1  0.205  0.414  0.164  1.0
  O  O30  1  0.233  0.695  0.159  1.0
  O  O31  1  0.702  0.407  0.085  1.0
  O  O32  1  0.586  0.823  0.026  1.0
  O  O33  1  0.598  0.596  0.637  1.0
  O  O34  1  0.767  0.305  0.841  1.0
  O  O35  1  0.670  0.921  0.649  1.0
  O  O36  1  0.706  0.083  0.386  1.0
  O  O37  1  0.537  0.770  0.379  1.0
  O  O38  1  0.402  0.404  0.363  1.0
  O  O39  1  0.414  0.177  0.974  1.0
  O  O40  1  0.111  0.314  0.560  1.0
  O  O41  1  0.294  0.917  0.614  1.0
  O  O42  1  0.090  0.122  0.158  1.0
  O  O43  1  0.243  0.526  0.608  1.0
[/CIF]
.