data_Si
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.49
_cell_length_b   4.49
_cell_length_c   3.74
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   116.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Si
_chemical_formula_sum   Si4
_cell_volume   67.74
_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  0.38  0.31  0.56  1.0
  Si  Si1  1  0.38  0.69  0.18  1.0
  Si  Si2  1  0.38  0.12  0.31  1.0
  Si  Si3  1  0.38  0.88  0.43  1.0

data_Si
_symmetry_space_group_name_H-M   P-1
_cell_length_a   3.74
_cell_length_b   4.49
_cell_length_c   4.49
_cell_angle_alpha   116.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   2
_chemical_formula_structural   Si
_chemical_formula_sum   Si4
_cell_volume   67.74
_cell_formula_units_Z   4
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-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  2  0.06  0.0  0.88  1.0
  Si  Si1  2  0.19  0.0  0.31  1.0

Si Si Si Si
Si is Hg_xSn structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of one tetrasilane molecule. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted single-bond geometry to one Si(2) atom. The Si(1)-Si(2) bond length is 1.28 Å. In the second Si site, Si(2) is bonded in a water-like geometry to one Si(1) and one Si(2) atom. The Si(2)-Si(2) bond length is 1.16 Å.