The compound described by Na2Cr2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), 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(6), one O(7), and two equivalent O(5) atoms. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form corner-sharing CrO4 tetrahedra. In the second Cr site, Cr(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing CrO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Na(1), one Na(2), and one Cr(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Na(1), one Na(2), and one Cr(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one Cr(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Na(1) and one Cr(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(1), two equivalent Na(2), and one Cr(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one Cr(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to one Na(2), one Cr(1), and one Cr(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Na2Cr2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.713
_cell_length_b   6.875
_cell_length_c   7.182
_cell_angle_alpha   113.592
_cell_angle_beta   89.895
_cell_angle_gamma   94.518
_symmetry_Int_Tables_number   1
_cell_volume   302.632
_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  0.620  0.262  0.353  1.0
  Na  Na1  1  0.380  0.738  0.647  1.0
  Na  Na2  1  0.868  0.118  0.755  1.0
  Na  Na3  1  0.132  0.882  0.245  1.0
  Cr  Cr4  1  0.885  0.648  0.811  1.0
  Cr  Cr5  1  0.115  0.352  0.189  1.0
  Cr  Cr6  1  0.652  0.755  0.238  1.0
  Cr  Cr7  1  0.348  0.245  0.762  1.0
  O  O8  1  0.884  0.409  0.637  1.0
  O  O9  1  0.116  0.591  0.363  1.0
  O  O10  1  0.733  0.785  0.750  1.0
  O  O11  1  0.267  0.215  0.250  1.0
  O  O12  1  0.106  0.773  0.857  1.0
  O  O13  1  0.894  0.227  0.143  1.0
  O  O14  1  0.570  0.592  0.337  1.0
  O  O15  1  0.430  0.408  0.663  1.0
  O  O16  1  0.781  0.961  0.405  1.0
  O  O17  1  0.219  0.039  0.595  1.0
  O  O18  1  0.468  0.837  0.154  1.0
  O  O19  1  0.532  0.163  0.846  1.0
  O  O20  1  0.812  0.628  0.040  1.0
  O  O21  1  0.188  0.372  0.960  1.0
[/CIF]
.
The compound described by Na2Cr2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), one O(3), one O(5), one O(6), 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(6), one O(7), and two equivalent O(5) atoms. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(1), one O(2), one O(3), and one O(7) atom to form corner-sharing CrO4 tetrahedra. In the second Cr site, Cr(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing CrO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to one Na(1), one Na(2), and one Cr(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Na(1), one Na(2), and one Cr(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one Cr(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Na(1) and one Cr(2) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(1), two equivalent Na(2), and one Cr(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Na(1), one Na(2), and one Cr(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to one Na(2), one Cr(1), and one Cr(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Na2Cr2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.713
_cell_length_b   6.875
_cell_length_c   7.182
_cell_angle_alpha   113.592
_cell_angle_beta   89.895
_cell_angle_gamma   94.518
_symmetry_Int_Tables_number   1
_cell_volume   302.632
_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  0.620  0.262  0.353  1.0
  Na  Na1  1  0.380  0.738  0.647  1.0
  Na  Na2  1  0.868  0.118  0.755  1.0
  Na  Na3  1  0.132  0.882  0.245  1.0
  Cr  Cr4  1  0.885  0.648  0.811  1.0
  Cr  Cr5  1  0.115  0.352  0.189  1.0
  Cr  Cr6  1  0.652  0.755  0.238  1.0
  Cr  Cr7  1  0.348  0.245  0.762  1.0
  O  O8  1  0.884  0.409  0.637  1.0
  O  O9  1  0.116  0.591  0.363  1.0
  O  O10  1  0.733  0.785  0.750  1.0
  O  O11  1  0.267  0.215  0.250  1.0
  O  O12  1  0.106  0.773  0.857  1.0
  O  O13  1  0.894  0.227  0.143  1.0
  O  O14  1  0.570  0.592  0.337  1.0
  O  O15  1  0.430  0.408  0.663  1.0
  O  O16  1  0.781  0.961  0.405  1.0
  O  O17  1  0.219  0.039  0.595  1.0
  O  O18  1  0.468  0.837  0.154  1.0
  O  O19  1  0.532  0.163  0.846  1.0
  O  O20  1  0.812  0.628  0.040  1.0
  O  O21  1  0.188  0.372  0.960  1.0
[/CIF]
.