The compound described by SiPb2Se4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Pb sites. In the first Pb site, Pb(1) is bonded in a 3-coordinate geometry to one Se(2), one Se(3), and one Se(4) atom. In the second Pb site, Pb(2) is bonded to one Se(2), one Se(3), one Se(4), and two equivalent Se(1) atoms to form PbSe5 square pyramids that share  a cornercorner with one Si(1)Se4 tetrahedra,  an edgeedge with one Pb(2)Se5 square pyramid, and edges with two equivalent Si(1)Se4 tetrahedra. 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 Pb(2)Se5 square pyramid and edges with two equivalent Pb(2)Se5 square pyramids. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted single-bond geometry to two equivalent Pb(2) and one Si(1) atom. In the second Se site, Se(2) is bonded in a distorted single-bond geometry to one Pb(1), one Pb(2), and one Si(1) atom. In the third Se site, Se(3) is bonded in a distorted single-bond geometry to one Pb(1), one Pb(2), and one Si(1) atom. In the fourth Se site, Se(4) is bonded in a distorted single-bond geometry to one Pb(1), one Pb(2), and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Si(PbSe2)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.286
_cell_length_b   8.690
_cell_length_c   13.850
_cell_angle_alpha   71.967
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   833.859
_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
  Si  Si0  1  0.747  0.203  0.356  1.0
  Si  Si1  1  0.247  0.797  0.144  1.0
  Si  Si2  1  0.253  0.797  0.644  1.0
  Si  Si3  1  0.753  0.203  0.856  1.0
  Pb  Pb4  1  0.641  0.557  0.138  1.0
  Pb  Pb5  1  0.141  0.443  0.362  1.0
  Pb  Pb6  1  0.359  0.443  0.862  1.0
  Pb  Pb7  1  0.859  0.557  0.638  1.0
  Pb  Pb8  1  0.647  0.056  0.127  1.0
  Pb  Pb9  1  0.147  0.944  0.373  1.0
  Pb  Pb10  1  0.353  0.944  0.873  1.0
  Pb  Pb11  1  0.853  0.056  0.627  1.0
  Se  Se12  1  0.765  0.934  0.445  1.0
  Se  Se13  1  0.265  0.066  0.055  1.0
  Se  Se14  1  0.235  0.066  0.555  1.0
  Se  Se15  1  0.735  0.934  0.945  1.0
  Se  Se16  1  0.523  0.269  0.738  1.0
  Se  Se17  1  0.023  0.731  0.762  1.0
  Se  Se18  1  0.477  0.731  0.262  1.0
  Se  Se19  1  0.977  0.269  0.238  1.0
  Se  Se20  1  0.519  0.746  0.734  1.0
  Se  Se21  1  0.019  0.254  0.766  1.0
  Se  Se22  1  0.481  0.254  0.266  1.0
  Se  Se23  1  0.981  0.746  0.234  1.0
  Se  Se24  1  0.725  0.365  0.957  1.0
  Se  Se25  1  0.225  0.635  0.543  1.0
  Se  Se26  1  0.275  0.635  0.043  1.0
  Se  Se27  1  0.775  0.365  0.457  1.0
[/CIF]
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The compound described by SiPb2Se4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Pb sites. In the first Pb site, Pb(1) is bonded in a 3-coordinate geometry to one Se(2), one Se(3), and one Se(4) atom. In the second Pb site, Pb(2) is bonded to one Se(2), one Se(3), one Se(4), and two equivalent Se(1) atoms to form PbSe5 square pyramids that share  a cornercorner with one Si(1)Se4 tetrahedra,  an edgeedge with one Pb(2)Se5 square pyramid, and edges with two equivalent Si(1)Se4 tetrahedra. 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 Pb(2)Se5 square pyramid and edges with two equivalent Pb(2)Se5 square pyramids. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted single-bond geometry to two equivalent Pb(2) and one Si(1) atom. In the second Se site, Se(2) is bonded in a distorted single-bond geometry to one Pb(1), one Pb(2), and one Si(1) atom. In the third Se site, Se(3) is bonded in a distorted single-bond geometry to one Pb(1), one Pb(2), and one Si(1) atom. In the fourth Se site, Se(4) is bonded in a distorted single-bond geometry to one Pb(1), one Pb(2), and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Si(PbSe2)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.286
_cell_length_b   8.690
_cell_length_c   13.850
_cell_angle_alpha   71.967
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   833.859
_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
  Si  Si0  1  0.747  0.203  0.356  1.0
  Si  Si1  1  0.247  0.797  0.144  1.0
  Si  Si2  1  0.253  0.797  0.644  1.0
  Si  Si3  1  0.753  0.203  0.856  1.0
  Pb  Pb4  1  0.641  0.557  0.138  1.0
  Pb  Pb5  1  0.141  0.443  0.362  1.0
  Pb  Pb6  1  0.359  0.443  0.862  1.0
  Pb  Pb7  1  0.859  0.557  0.638  1.0
  Pb  Pb8  1  0.647  0.056  0.127  1.0
  Pb  Pb9  1  0.147  0.944  0.373  1.0
  Pb  Pb10  1  0.353  0.944  0.873  1.0
  Pb  Pb11  1  0.853  0.056  0.627  1.0
  Se  Se12  1  0.765  0.934  0.445  1.0
  Se  Se13  1  0.265  0.066  0.055  1.0
  Se  Se14  1  0.235  0.066  0.555  1.0
  Se  Se15  1  0.735  0.934  0.945  1.0
  Se  Se16  1  0.523  0.269  0.738  1.0
  Se  Se17  1  0.023  0.731  0.762  1.0
  Se  Se18  1  0.477  0.731  0.262  1.0
  Se  Se19  1  0.977  0.269  0.238  1.0
  Se  Se20  1  0.519  0.746  0.734  1.0
  Se  Se21  1  0.019  0.254  0.766  1.0
  Se  Se22  1  0.481  0.254  0.266  1.0
  Se  Se23  1  0.981  0.746  0.234  1.0
  Se  Se24  1  0.725  0.365  0.957  1.0
  Se  Se25  1  0.225  0.635  0.543  1.0
  Se  Se26  1  0.275  0.635  0.043  1.0
  Se  Se27  1  0.775  0.365  0.457  1.0
[/CIF]
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