The crystal structure described by NaAsSe2 crystallizes in the monoclinic Pc space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to one Se(1), one Se(4), two equivalent Se(3), and two equivalent Se(7) atoms to form a mixture of corner and edge-sharing NaSe6 octahedra. The corner-sharing octahedral tilt angles range from 11-16°. In the second Na site, Na(2) is bonded to one Se(3), one Se(6), two equivalent Se(1), and two equivalent Se(2) atoms to form a mixture of corner and edge-sharing NaSe6 octahedra. The corner-sharing octahedral tilt angles range from 8-21°. In the third Na site, Na(3) is bonded to one Se(3), one Se(6), two equivalent Se(4), and two equivalent Se(8) atoms to form a mixture of corner and edge-sharing NaSe6 octahedra. The corner-sharing octahedral tilt angles range from 7-17°. In the fourth Na site, Na(4) is bonded to one Se(2), one Se(8), two equivalent Se(5), and two equivalent Se(6) atoms to form a mixture of corner and edge-sharing NaSe6 octahedra. The corner-sharing octahedral tilt angles range from 10-16°. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 3-coordinate geometry to one Se(2), one Se(3), and one Se(7) atom. In the second As site, As(2) is bonded in a trigonal non-coplanar geometry to one Se(4), one Se(7), and one Se(8) atom. In the third As site, As(3) is bonded in a 3-coordinate geometry to one Se(4), one Se(5), and one Se(6) atom. In the fourth As site, As(4) is bonded in a trigonal non-coplanar geometry to one Se(1), one Se(2), and one Se(5) atom. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), two equivalent Na(2), and one As(4) atom. In the second Se site, Se(2) is bonded to one Na(4), two equivalent Na(2), one As(1), and one As(4) atom to form distorted SeNa3As2 trigonal bipyramids that share  a cornercorner with one Se(3)Na4As square pyramid, corners with two equivalent Se(2)Na3As2 trigonal bipyramids,  an edgeedge with one Se(3)Na4As square pyramid, and edges with two equivalent Se(6)Na4As square pyramids. In the third Se site, Se(3) is bonded to one Na(2), one Na(3), two equivalent Na(1), and one As(1) atom to form SeNa4As square pyramids that share corners with two equivalent Se(3)Na4As square pyramids, corners with two equivalent Se(6)Na4As square pyramids,  a cornercorner with one Se(2)Na3As2 trigonal bipyramid,  an edgeedge with one Se(2)Na3As2 trigonal bipyramid, and edges with two equivalent Se(4)Na3As2 trigonal bipyramids. In the fourth Se site, Se(4) is bonded to one Na(1), two equivalent Na(3), one As(2), and one As(3) atom to form distorted SeNa3As2 trigonal bipyramids that share  a cornercorner with one Se(6)Na4As square pyramid, corners with two equivalent Se(4)Na3As2 trigonal bipyramids,  an edgeedge with one Se(6)Na4As square pyramid, and edges with two equivalent Se(3)Na4As square pyramids. In the fifth Se site, Se(5) is bonded in a rectangular see-saw-like geometry to two equivalent Na(4), one As(3), and one As(4) atom. In the sixth Se site, Se(6) is bonded to one Na(2), one Na(3), two equivalent Na(4), and one As(3) atom to form SeNa4As square pyramids that share corners with two equivalent Se(3)Na4As square pyramids, corners with two equivalent Se(6)Na4As square pyramids,  a cornercorner with one Se(4)Na3As2 trigonal bipyramid,  an edgeedge with one Se(4)Na3As2 trigonal bipyramid, and edges with two equivalent Se(2)Na3As2 trigonal bipyramids. In the seventh Se site, Se(7) is bonded in a rectangular see-saw-like geometry to two equivalent Na(1), one As(1), and one As(2) atom. In the eighth Se site, Se(8) is bonded in a distorted rectangular see-saw-like geometry to one Na(4), two equivalent Na(3), and one As(2) atom. is represented by the CIF file [CIF]
data_NaAsSe2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.991
_cell_length_b   11.763
_cell_length_c   11.982
_cell_angle_alpha   89.017
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   844.266
_cell_formula_units_Z   8
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  0.014  0.762  0.245  1.0
  Na  Na1  1  0.986  0.762  0.745  1.0
  Na  Na2  1  0.500  0.519  0.741  1.0
  Na  Na3  1  0.500  0.519  0.241  1.0
  Na  Na4  1  0.523  0.020  0.764  1.0
  Na  Na5  1  0.477  0.020  0.264  1.0
  Na  Na6  1  0.470  0.260  0.500  1.0
  Na  Na7  1  0.530  0.260  0.000  1.0
  As  As8  1  0.455  0.749  0.963  1.0
  As  As9  1  0.545  0.749  0.463  1.0
  As  As10  1  0.095  0.998  0.997  1.0
  As  As11  1  0.905  0.998  0.497  1.0
  As  As12  1  0.075  0.252  0.776  1.0
  As  As13  1  0.925  0.252  0.276  1.0
  As  As14  1  0.018  0.499  0.950  1.0
  As  As15  1  0.982  0.499  0.450  1.0
  Se  Se16  1  0.001  0.511  0.256  1.0
  Se  Se17  1  0.999  0.511  0.756  1.0
  Se  Se18  1  0.413  0.536  0.990  1.0
  Se  Se19  1  0.587  0.536  0.490  1.0
  Se  Se20  1  0.484  0.770  0.769  1.0
  Se  Se21  1  0.516  0.770  0.269  1.0
  Se  Se22  1  0.026  0.038  0.798  1.0
  Se  Se23  1  0.974  0.038  0.298  1.0
  Se  Se24  1  0.031  0.288  0.977  1.0
  Se  Se25  1  0.969  0.288  0.477  1.0
  Se  Se26  1  0.461  0.269  0.750  1.0
  Se  Se27  1  0.539  0.269  0.250  1.0
  Se  Se28  1  0.054  0.786  0.994  1.0
  Se  Se29  1  0.946  0.786  0.494  1.0
  Se  Se30  1  0.519  0.009  0.513  1.0
  Se  Se31  1  0.481  0.009  0.013  1.0
[/CIF]
.
The crystal structure described by NaAsSe2 crystallizes in the monoclinic Pc space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to one Se(1), one Se(4), two equivalent Se(3), and two equivalent Se(7) atoms to form a mixture of corner and edge-sharing NaSe6 octahedra. The corner-sharing octahedral tilt angles range from 11-16°. In the second Na site, Na(2) is bonded to one Se(3), one Se(6), two equivalent Se(1), and two equivalent Se(2) atoms to form a mixture of corner and edge-sharing NaSe6 octahedra. The corner-sharing octahedral tilt angles range from 8-21°. In the third Na site, Na(3) is bonded to one Se(3), one Se(6), two equivalent Se(4), and two equivalent Se(8) atoms to form a mixture of corner and edge-sharing NaSe6 octahedra. The corner-sharing octahedral tilt angles range from 7-17°. In the fourth Na site, Na(4) is bonded to one Se(2), one Se(8), two equivalent Se(5), and two equivalent Se(6) atoms to form a mixture of corner and edge-sharing NaSe6 octahedra. The corner-sharing octahedral tilt angles range from 10-16°. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 3-coordinate geometry to one Se(2), one Se(3), and one Se(7) atom. In the second As site, As(2) is bonded in a trigonal non-coplanar geometry to one Se(4), one Se(7), and one Se(8) atom. In the third As site, As(3) is bonded in a 3-coordinate geometry to one Se(4), one Se(5), and one Se(6) atom. In the fourth As site, As(4) is bonded in a trigonal non-coplanar geometry to one Se(1), one Se(2), and one Se(5) atom. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), two equivalent Na(2), and one As(4) atom. In the second Se site, Se(2) is bonded to one Na(4), two equivalent Na(2), one As(1), and one As(4) atom to form distorted SeNa3As2 trigonal bipyramids that share  a cornercorner with one Se(3)Na4As square pyramid, corners with two equivalent Se(2)Na3As2 trigonal bipyramids,  an edgeedge with one Se(3)Na4As square pyramid, and edges with two equivalent Se(6)Na4As square pyramids. In the third Se site, Se(3) is bonded to one Na(2), one Na(3), two equivalent Na(1), and one As(1) atom to form SeNa4As square pyramids that share corners with two equivalent Se(3)Na4As square pyramids, corners with two equivalent Se(6)Na4As square pyramids,  a cornercorner with one Se(2)Na3As2 trigonal bipyramid,  an edgeedge with one Se(2)Na3As2 trigonal bipyramid, and edges with two equivalent Se(4)Na3As2 trigonal bipyramids. In the fourth Se site, Se(4) is bonded to one Na(1), two equivalent Na(3), one As(2), and one As(3) atom to form distorted SeNa3As2 trigonal bipyramids that share  a cornercorner with one Se(6)Na4As square pyramid, corners with two equivalent Se(4)Na3As2 trigonal bipyramids,  an edgeedge with one Se(6)Na4As square pyramid, and edges with two equivalent Se(3)Na4As square pyramids. In the fifth Se site, Se(5) is bonded in a rectangular see-saw-like geometry to two equivalent Na(4), one As(3), and one As(4) atom. In the sixth Se site, Se(6) is bonded to one Na(2), one Na(3), two equivalent Na(4), and one As(3) atom to form SeNa4As square pyramids that share corners with two equivalent Se(3)Na4As square pyramids, corners with two equivalent Se(6)Na4As square pyramids,  a cornercorner with one Se(4)Na3As2 trigonal bipyramid,  an edgeedge with one Se(4)Na3As2 trigonal bipyramid, and edges with two equivalent Se(2)Na3As2 trigonal bipyramids. In the seventh Se site, Se(7) is bonded in a rectangular see-saw-like geometry to two equivalent Na(1), one As(1), and one As(2) atom. In the eighth Se site, Se(8) is bonded in a distorted rectangular see-saw-like geometry to one Na(4), two equivalent Na(3), and one As(2) atom. is represented by the CIF file [CIF]
data_NaAsSe2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.991
_cell_length_b   11.763
_cell_length_c   11.982
_cell_angle_alpha   89.017
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   844.266
_cell_formula_units_Z   8
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  0.014  0.762  0.245  1.0
  Na  Na1  1  0.986  0.762  0.745  1.0
  Na  Na2  1  0.500  0.519  0.741  1.0
  Na  Na3  1  0.500  0.519  0.241  1.0
  Na  Na4  1  0.523  0.020  0.764  1.0
  Na  Na5  1  0.477  0.020  0.264  1.0
  Na  Na6  1  0.470  0.260  0.500  1.0
  Na  Na7  1  0.530  0.260  0.000  1.0
  As  As8  1  0.455  0.749  0.963  1.0
  As  As9  1  0.545  0.749  0.463  1.0
  As  As10  1  0.095  0.998  0.997  1.0
  As  As11  1  0.905  0.998  0.497  1.0
  As  As12  1  0.075  0.252  0.776  1.0
  As  As13  1  0.925  0.252  0.276  1.0
  As  As14  1  0.018  0.499  0.950  1.0
  As  As15  1  0.982  0.499  0.450  1.0
  Se  Se16  1  0.001  0.511  0.256  1.0
  Se  Se17  1  0.999  0.511  0.756  1.0
  Se  Se18  1  0.413  0.536  0.990  1.0
  Se  Se19  1  0.587  0.536  0.490  1.0
  Se  Se20  1  0.484  0.770  0.769  1.0
  Se  Se21  1  0.516  0.770  0.269  1.0
  Se  Se22  1  0.026  0.038  0.798  1.0
  Se  Se23  1  0.974  0.038  0.298  1.0
  Se  Se24  1  0.031  0.288  0.977  1.0
  Se  Se25  1  0.969  0.288  0.477  1.0
  Se  Se26  1  0.461  0.269  0.750  1.0
  Se  Se27  1  0.539  0.269  0.250  1.0
  Se  Se28  1  0.054  0.786  0.994  1.0
  Se  Se29  1  0.946  0.786  0.494  1.0
  Se  Se30  1  0.519  0.009  0.513  1.0
  Se  Se31  1  0.481  0.009  0.013  1.0
[/CIF]
.