The compound described by Mg9Si5 crystallizes in the trigonal R-3c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(3), two equivalent Si(1), and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded to two equivalent Si(1) and two equivalent Si(2) atoms to form a mixture of distorted corner and edge-sharing MgSi4 tetrahedra. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to three equivalent Mg(2) and six equivalent Mg(1) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Mg(2) and six equivalent Mg(1) atoms. In the third Si site, Si(3) is bonded in a 6-coordinate geometry to six equivalent Mg(1) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg9Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   12.830
_cell_length_b   12.830
_cell_length_c   12.830
_cell_angle_alpha   32.541
_cell_angle_beta   32.541
_cell_angle_gamma   32.541
_symmetry_Int_Tables_number   1
_cell_volume   543.445
_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
  Mg  Mg0  1  0.349  0.888  0.675  1.0
  Mg  Mg1  1  0.996  0.250  0.504  1.0
  Mg  Mg2  1  0.888  0.675  0.349  1.0
  Mg  Mg3  1  0.250  0.504  0.996  1.0
  Mg  Mg4  1  0.675  0.349  0.888  1.0
  Mg  Mg5  1  0.504  0.996  0.250  1.0
  Mg  Mg6  1  0.849  0.175  0.388  1.0
  Mg  Mg7  1  0.496  0.004  0.750  1.0
  Mg  Mg8  1  0.175  0.388  0.849  1.0
  Mg  Mg9  1  0.004  0.750  0.496  1.0
  Mg  Mg10  1  0.388  0.849  0.175  1.0
  Mg  Mg11  1  0.750  0.496  0.004  1.0
  Mg  Mg12  1  0.612  0.151  0.825  1.0
  Mg  Mg13  1  0.651  0.112  0.325  1.0
  Mg  Mg14  1  0.151  0.825  0.612  1.0
  Mg  Mg15  1  0.112  0.325  0.651  1.0
  Mg  Mg16  1  0.825  0.612  0.151  1.0
  Mg  Mg17  1  0.325  0.651  0.112  1.0
  Si  Si18  1  0.079  0.079  0.079  1.0
  Si  Si19  1  0.193  0.193  0.193  1.0
  Si  Si20  1  0.921  0.921  0.921  1.0
  Si  Si21  1  0.000  0.000  0.000  1.0
  Si  Si22  1  0.807  0.807  0.807  1.0
  Si  Si23  1  0.307  0.307  0.307  1.0
  Si  Si24  1  0.421  0.421  0.421  1.0
  Si  Si25  1  0.693  0.693  0.693  1.0
  Si  Si26  1  0.579  0.579  0.579  1.0
  Si  Si27  1  0.500  0.500  0.500  1.0
[/CIF]
.
The compound described by Mg9Si5 crystallizes in the trigonal R-3c space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(3), two equivalent Si(1), and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded to two equivalent Si(1) and two equivalent Si(2) atoms to form a mixture of distorted corner and edge-sharing MgSi4 tetrahedra. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to three equivalent Mg(2) and six equivalent Mg(1) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Mg(2) and six equivalent Mg(1) atoms. In the third Si site, Si(3) is bonded in a 6-coordinate geometry to six equivalent Mg(1) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg9Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   12.830
_cell_length_b   12.830
_cell_length_c   12.830
_cell_angle_alpha   32.541
_cell_angle_beta   32.541
_cell_angle_gamma   32.541
_symmetry_Int_Tables_number   1
_cell_volume   543.445
_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
  Mg  Mg0  1  0.349  0.888  0.675  1.0
  Mg  Mg1  1  0.996  0.250  0.504  1.0
  Mg  Mg2  1  0.888  0.675  0.349  1.0
  Mg  Mg3  1  0.250  0.504  0.996  1.0
  Mg  Mg4  1  0.675  0.349  0.888  1.0
  Mg  Mg5  1  0.504  0.996  0.250  1.0
  Mg  Mg6  1  0.849  0.175  0.388  1.0
  Mg  Mg7  1  0.496  0.004  0.750  1.0
  Mg  Mg8  1  0.175  0.388  0.849  1.0
  Mg  Mg9  1  0.004  0.750  0.496  1.0
  Mg  Mg10  1  0.388  0.849  0.175  1.0
  Mg  Mg11  1  0.750  0.496  0.004  1.0
  Mg  Mg12  1  0.612  0.151  0.825  1.0
  Mg  Mg13  1  0.651  0.112  0.325  1.0
  Mg  Mg14  1  0.151  0.825  0.612  1.0
  Mg  Mg15  1  0.112  0.325  0.651  1.0
  Mg  Mg16  1  0.825  0.612  0.151  1.0
  Mg  Mg17  1  0.325  0.651  0.112  1.0
  Si  Si18  1  0.079  0.079  0.079  1.0
  Si  Si19  1  0.193  0.193  0.193  1.0
  Si  Si20  1  0.921  0.921  0.921  1.0
  Si  Si21  1  0.000  0.000  0.000  1.0
  Si  Si22  1  0.807  0.807  0.807  1.0
  Si  Si23  1  0.307  0.307  0.307  1.0
  Si  Si24  1  0.421  0.421  0.421  1.0
  Si  Si25  1  0.693  0.693  0.693  1.0
  Si  Si26  1  0.579  0.579  0.579  1.0
  Si  Si27  1  0.500  0.500  0.500  1.0
[/CIF]
.