The compound described by Na6Si2Se7 crystallizes in the monoclinic C2/c space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to two equivalent Se(2) and two equivalent Se(4) atoms. In the second Na site, Na(2) is bonded to two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form NaSe6 octahedra that share corners with two equivalent Si(1)Se4 tetrahedra and edges with two equivalent Si(1)Se4 tetrahedra. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to one Se(1), one Se(4), two equivalent Se(2), and two equivalent Se(3) atoms. In the fourth Na site, Na(4) is bonded in a 6-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. Si(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form SiSe4 tetrahedra that share  a cornercorner with one Na(2)Se6 octahedra,  a cornercorner with one Si(1)Se4 tetrahedra, and  an edgeedge with one Na(2)Se6 octahedra. The corner-sharing octahedral tilt angles are 19°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted bent 120 degrees geometry to two equivalent Na(3), two equivalent Na(4), and two equivalent Si(1) atoms. In the second Se site, Se(2) is bonded to one Na(1), one Na(2), one Na(4), two equivalent Na(3), and one Si(1) atom to form a mixture of distorted corner and edge-sharing SeNa5Si octahedra. The corner-sharing octahedral tilt angles range from 0-78°. In the third Se site, Se(3) is bonded to one Na(2), two equivalent Na(3), two equivalent Na(4), and one Si(1) atom to form a mixture of corner and edge-sharing SeNa5Si octahedra. The corner-sharing octahedral tilt angles range from 0-4°. In the fourth Se site, Se(4) is bonded in a 6-coordinate geometry to one Na(1), one Na(2), one Na(3), two equivalent Na(4), and one Si(1) atom. is represented by the CIF card [CIF]
data_Na6Si2Se7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.156
_cell_length_b   7.156
_cell_length_c   15.721
_cell_angle_alpha   80.227
_cell_angle_beta   80.227
_cell_angle_gamma   98.038
_symmetry_Int_Tables_number   1
_cell_volume   770.007
_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  0.579  0.421  0.750  1.0
  Na  Na1  1  0.421  0.579  0.250  1.0
  Na  Na2  1  0.500  0.500  0.000  1.0
  Na  Na3  1  0.500  0.500  0.500  1.0
  Na  Na4  1  0.266  0.972  0.927  1.0
  Na  Na5  1  0.028  0.734  0.573  1.0
  Na  Na6  1  0.734  0.028  0.073  1.0
  Na  Na7  1  0.972  0.266  0.427  1.0
  Na  Na8  1  0.510  0.952  0.640  1.0
  Na  Na9  1  0.048  0.490  0.860  1.0
  Na  Na10  1  0.490  0.048  0.360  1.0
  Na  Na11  1  0.952  0.510  0.140  1.0
  Si  Si12  1  0.763  0.924  0.861  1.0
  Si  Si13  1  0.076  0.237  0.639  1.0
  Si  Si14  1  0.924  0.763  0.361  1.0
  Si  Si15  1  0.237  0.076  0.139  1.0
  Se  Se16  1  0.036  0.964  0.750  1.0
  Se  Se17  1  0.964  0.036  0.250  1.0
  Se  Se18  1  0.690  0.202  0.894  1.0
  Se  Se19  1  0.798  0.310  0.606  1.0
  Se  Se20  1  0.310  0.798  0.106  1.0
  Se  Se21  1  0.202  0.690  0.394  1.0
  Se  Se22  1  0.869  0.741  0.970  1.0
  Se  Se23  1  0.259  0.131  0.530  1.0
  Se  Se24  1  0.131  0.259  0.030  1.0
  Se  Se25  1  0.741  0.869  0.470  1.0
  Se  Se26  1  0.509  0.756  0.822  1.0
  Se  Se27  1  0.244  0.491  0.678  1.0
  Se  Se28  1  0.491  0.244  0.178  1.0
  Se  Se29  1  0.756  0.509  0.322  1.0
[/CIF]
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The compound described by Na6Si2Se7 crystallizes in the monoclinic C2/c space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to two equivalent Se(2) and two equivalent Se(4) atoms. In the second Na site, Na(2) is bonded to two equivalent Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form NaSe6 octahedra that share corners with two equivalent Si(1)Se4 tetrahedra and edges with two equivalent Si(1)Se4 tetrahedra. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to one Se(1), one Se(4), two equivalent Se(2), and two equivalent Se(3) atoms. In the fourth Na site, Na(4) is bonded in a 6-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. Si(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form SiSe4 tetrahedra that share  a cornercorner with one Na(2)Se6 octahedra,  a cornercorner with one Si(1)Se4 tetrahedra, and  an edgeedge with one Na(2)Se6 octahedra. The corner-sharing octahedral tilt angles are 19°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted bent 120 degrees geometry to two equivalent Na(3), two equivalent Na(4), and two equivalent Si(1) atoms. In the second Se site, Se(2) is bonded to one Na(1), one Na(2), one Na(4), two equivalent Na(3), and one Si(1) atom to form a mixture of distorted corner and edge-sharing SeNa5Si octahedra. The corner-sharing octahedral tilt angles range from 0-78°. In the third Se site, Se(3) is bonded to one Na(2), two equivalent Na(3), two equivalent Na(4), and one Si(1) atom to form a mixture of corner and edge-sharing SeNa5Si octahedra. The corner-sharing octahedral tilt angles range from 0-4°. In the fourth Se site, Se(4) is bonded in a 6-coordinate geometry to one Na(1), one Na(2), one Na(3), two equivalent Na(4), and one Si(1) atom. is represented by the CIF card [CIF]
data_Na6Si2Se7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.156
_cell_length_b   7.156
_cell_length_c   15.721
_cell_angle_alpha   80.227
_cell_angle_beta   80.227
_cell_angle_gamma   98.038
_symmetry_Int_Tables_number   1
_cell_volume   770.007
_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  0.579  0.421  0.750  1.0
  Na  Na1  1  0.421  0.579  0.250  1.0
  Na  Na2  1  0.500  0.500  0.000  1.0
  Na  Na3  1  0.500  0.500  0.500  1.0
  Na  Na4  1  0.266  0.972  0.927  1.0
  Na  Na5  1  0.028  0.734  0.573  1.0
  Na  Na6  1  0.734  0.028  0.073  1.0
  Na  Na7  1  0.972  0.266  0.427  1.0
  Na  Na8  1  0.510  0.952  0.640  1.0
  Na  Na9  1  0.048  0.490  0.860  1.0
  Na  Na10  1  0.490  0.048  0.360  1.0
  Na  Na11  1  0.952  0.510  0.140  1.0
  Si  Si12  1  0.763  0.924  0.861  1.0
  Si  Si13  1  0.076  0.237  0.639  1.0
  Si  Si14  1  0.924  0.763  0.361  1.0
  Si  Si15  1  0.237  0.076  0.139  1.0
  Se  Se16  1  0.036  0.964  0.750  1.0
  Se  Se17  1  0.964  0.036  0.250  1.0
  Se  Se18  1  0.690  0.202  0.894  1.0
  Se  Se19  1  0.798  0.310  0.606  1.0
  Se  Se20  1  0.310  0.798  0.106  1.0
  Se  Se21  1  0.202  0.690  0.394  1.0
  Se  Se22  1  0.869  0.741  0.970  1.0
  Se  Se23  1  0.259  0.131  0.530  1.0
  Se  Se24  1  0.131  0.259  0.030  1.0
  Se  Se25  1  0.741  0.869  0.470  1.0
  Se  Se26  1  0.509  0.756  0.822  1.0
  Se  Se27  1  0.244  0.491  0.678  1.0
  Se  Se28  1  0.491  0.244  0.178  1.0
  Se  Se29  1  0.756  0.509  0.322  1.0
[/CIF]
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