The material described by Na2NbAsO6 crystallizes in the monoclinic C2/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(6), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(6) and four equivalent O(3) atoms. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Nb(1) is bonded to one O(1), one O(2), one O(5), one O(6), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra and corners with three equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 40°. As(1) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form AsO4 tetrahedra that share corners with three equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-50°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), two equivalent Na(3), and one Nb(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(3), one Nb(1), and one As(1) atom. In the third O site, O(3) is bonded to one Na(1), two equivalent Na(2), and one As(1) atom to form distorted ONa3As trigonal pyramids that share corners with two equivalent O(6)Na2NbAs trigonal pyramids, corners with four equivalent O(3)Na3As trigonal pyramids,  an edgeedge with one O(3)Na3As trigonal pyramid, and edges with two equivalent O(6)Na2NbAs trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Na(1) and two equivalent Nb(1) atoms. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(1), one Nb(1), and one As(1) atom. In the sixth O site, O(6) is bonded to one Na(1), one Na(2), one Nb(1), and one As(1) atom to form distorted ONa2NbAs trigonal pyramids that share  a cornercorner with one O(6)Na2NbAs trigonal pyramid, corners with two equivalent O(3)Na3As trigonal pyramids, and edges with two equivalent O(3)Na3As trigonal pyramids. is represented by the CIF file [CIF]
data_Na2NbAsO6
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.232
_cell_length_b   9.232
_cell_length_c   7.429
_cell_angle_alpha   75.278
_cell_angle_beta   75.278
_cell_angle_gamma   73.035
_symmetry_Int_Tables_number   1
_cell_volume   574.482
_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  0.352  0.930  0.940  1.0
  Na  Na1  1  0.930  0.352  0.440  1.0
  Na  Na2  1  0.648  0.070  0.060  1.0
  Na  Na3  1  0.005  0.995  0.750  1.0
  Na  Na4  1  0.070  0.648  0.560  1.0
  Na  Na5  1  0.546  0.454  0.250  1.0
  Na  Na6  1  0.995  0.005  0.250  1.0
  Na  Na7  1  0.454  0.546  0.750  1.0
  Nb  Nb8  1  0.708  0.713  0.384  1.0
  Nb  Nb9  1  0.713  0.708  0.884  1.0
  Nb  Nb10  1  0.287  0.292  0.116  1.0
  Nb  Nb11  1  0.292  0.287  0.616  1.0
  As  As12  1  0.059  0.684  0.047  1.0
  As  As13  1  0.684  0.059  0.547  1.0
  As  As14  1  0.316  0.941  0.453  1.0
  As  As15  1  0.941  0.316  0.953  1.0
  O  O16  1  0.520  0.680  0.938  1.0
  O  O17  1  0.480  0.320  0.062  1.0
  O  O18  1  0.523  0.209  0.504  1.0
  O  O19  1  0.127  0.840  0.028  1.0
  O  O20  1  0.211  0.313  0.375  1.0
  O  O21  1  0.789  0.687  0.625  1.0
  O  O22  1  0.953  0.640  0.276  1.0
  O  O23  1  0.840  0.127  0.528  1.0
  O  O24  1  0.687  0.789  0.125  1.0
  O  O25  1  0.313  0.211  0.875  1.0
  O  O26  1  0.360  0.047  0.224  1.0
  O  O27  1  0.320  0.480  0.562  1.0
  O  O28  1  0.791  0.477  0.996  1.0
  O  O29  1  0.956  0.723  0.869  1.0
  O  O30  1  0.723  0.956  0.369  1.0
  O  O31  1  0.873  0.160  0.972  1.0
  O  O32  1  0.209  0.523  0.004  1.0
  O  O33  1  0.044  0.277  0.131  1.0
  O  O34  1  0.160  0.873  0.472  1.0
  O  O35  1  0.680  0.520  0.438  1.0
  O  O36  1  0.047  0.360  0.724  1.0
  O  O37  1  0.277  0.044  0.631  1.0
  O  O38  1  0.477  0.791  0.496  1.0
  O  O39  1  0.640  0.953  0.776  1.0
[/CIF]
.
The material described by Na2NbAsO6 crystallizes in the monoclinic C2/c space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(4), one O(6), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to two equivalent O(6) and four equivalent O(3) atoms. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Nb(1) is bonded to one O(1), one O(2), one O(5), one O(6), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra and corners with three equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 40°. As(1) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form AsO4 tetrahedra that share corners with three equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 39-50°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), two equivalent Na(3), and one Nb(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(3), one Nb(1), and one As(1) atom. In the third O site, O(3) is bonded to one Na(1), two equivalent Na(2), and one As(1) atom to form distorted ONa3As trigonal pyramids that share corners with two equivalent O(6)Na2NbAs trigonal pyramids, corners with four equivalent O(3)Na3As trigonal pyramids,  an edgeedge with one O(3)Na3As trigonal pyramid, and edges with two equivalent O(6)Na2NbAs trigonal pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Na(1) and two equivalent Nb(1) atoms. In the fifth O site, O(5) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(1), one Nb(1), and one As(1) atom. In the sixth O site, O(6) is bonded to one Na(1), one Na(2), one Nb(1), and one As(1) atom to form distorted ONa2NbAs trigonal pyramids that share  a cornercorner with one O(6)Na2NbAs trigonal pyramid, corners with two equivalent O(3)Na3As trigonal pyramids, and edges with two equivalent O(3)Na3As trigonal pyramids. is represented by the CIF file [CIF]
data_Na2NbAsO6
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.232
_cell_length_b   9.232
_cell_length_c   7.429
_cell_angle_alpha   75.278
_cell_angle_beta   75.278
_cell_angle_gamma   73.035
_symmetry_Int_Tables_number   1
_cell_volume   574.482
_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  0.352  0.930  0.940  1.0
  Na  Na1  1  0.930  0.352  0.440  1.0
  Na  Na2  1  0.648  0.070  0.060  1.0
  Na  Na3  1  0.005  0.995  0.750  1.0
  Na  Na4  1  0.070  0.648  0.560  1.0
  Na  Na5  1  0.546  0.454  0.250  1.0
  Na  Na6  1  0.995  0.005  0.250  1.0
  Na  Na7  1  0.454  0.546  0.750  1.0
  Nb  Nb8  1  0.708  0.713  0.384  1.0
  Nb  Nb9  1  0.713  0.708  0.884  1.0
  Nb  Nb10  1  0.287  0.292  0.116  1.0
  Nb  Nb11  1  0.292  0.287  0.616  1.0
  As  As12  1  0.059  0.684  0.047  1.0
  As  As13  1  0.684  0.059  0.547  1.0
  As  As14  1  0.316  0.941  0.453  1.0
  As  As15  1  0.941  0.316  0.953  1.0
  O  O16  1  0.520  0.680  0.938  1.0
  O  O17  1  0.480  0.320  0.062  1.0
  O  O18  1  0.523  0.209  0.504  1.0
  O  O19  1  0.127  0.840  0.028  1.0
  O  O20  1  0.211  0.313  0.375  1.0
  O  O21  1  0.789  0.687  0.625  1.0
  O  O22  1  0.953  0.640  0.276  1.0
  O  O23  1  0.840  0.127  0.528  1.0
  O  O24  1  0.687  0.789  0.125  1.0
  O  O25  1  0.313  0.211  0.875  1.0
  O  O26  1  0.360  0.047  0.224  1.0
  O  O27  1  0.320  0.480  0.562  1.0
  O  O28  1  0.791  0.477  0.996  1.0
  O  O29  1  0.956  0.723  0.869  1.0
  O  O30  1  0.723  0.956  0.369  1.0
  O  O31  1  0.873  0.160  0.972  1.0
  O  O32  1  0.209  0.523  0.004  1.0
  O  O33  1  0.044  0.277  0.131  1.0
  O  O34  1  0.160  0.873  0.472  1.0
  O  O35  1  0.680  0.520  0.438  1.0
  O  O36  1  0.047  0.360  0.724  1.0
  O  O37  1  0.277  0.044  0.631  1.0
  O  O38  1  0.477  0.791  0.496  1.0
  O  O39  1  0.640  0.953  0.776  1.0
[/CIF]
.