The structure described by MgSi2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 9-coordinate geometry to two equivalent Si(2), two equivalent Si(3), two equivalent Si(4), and three equivalent Si(1) atoms. In the second Mg site, Mg(2) is bonded to two equivalent Si(2) and four equivalent Si(1) atoms to form distorted MgSi6 octahedra that share corners with two equivalent Mg(3)Si12 cuboctahedra and edges with two equivalent Mg(2)Si6 octahedra. In the third Mg site, Mg(3) is bonded to two equivalent Si(2), four equivalent Si(4), and six equivalent Si(3) atoms to form distorted MgSi12 cuboctahedra that share corners with two equivalent Mg(2)Si6 octahedra, edges with four equivalent Mg(3)Si12 cuboctahedra, and faces with two equivalent Mg(3)Si12 cuboctahedra. The corner-sharing octahedral tilt angles are 23°. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to two equivalent Mg(2), three equivalent Mg(1), one Si(4), and two equivalent Si(1) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(1), one Si(3), and two equivalent Si(4) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Mg(1), three equivalent Mg(3), one Si(2), one Si(4), and two equivalent Si(3) atoms. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(3), one Si(1), one Si(3), and two equivalent Si(2) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_MgSi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.638
_cell_length_b   5.638
_cell_length_c   11.137
_cell_angle_alpha   73.813
_cell_angle_beta   73.813
_cell_angle_gamma   39.421
_symmetry_Int_Tables_number   1
_cell_volume   214.688
_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
  Mg  Mg0  1  0.212  0.212  0.294  1.0
  Mg  Mg1  1  0.500  0.500  0.500  1.0
  Mg  Mg2  1  0.788  0.788  0.706  1.0
  Mg  Mg3  1  0.500  0.500  0.000  1.0
  Si  Si4  1  0.184  0.184  0.547  1.0
  Si  Si5  1  0.555  0.555  0.231  1.0
  Si  Si6  1  0.767  0.767  0.068  1.0
  Si  Si7  1  0.085  0.085  0.782  1.0
  Si  Si8  1  0.915  0.915  0.218  1.0
  Si  Si9  1  0.816  0.816  0.453  1.0
  Si  Si10  1  0.445  0.445  0.769  1.0
  Si  Si11  1  0.233  0.233  0.932  1.0
[/CIF]
.
The structure described by MgSi2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 9-coordinate geometry to two equivalent Si(2), two equivalent Si(3), two equivalent Si(4), and three equivalent Si(1) atoms. In the second Mg site, Mg(2) is bonded to two equivalent Si(2) and four equivalent Si(1) atoms to form distorted MgSi6 octahedra that share corners with two equivalent Mg(3)Si12 cuboctahedra and edges with two equivalent Mg(2)Si6 octahedra. In the third Mg site, Mg(3) is bonded to two equivalent Si(2), four equivalent Si(4), and six equivalent Si(3) atoms to form distorted MgSi12 cuboctahedra that share corners with two equivalent Mg(2)Si6 octahedra, edges with four equivalent Mg(3)Si12 cuboctahedra, and faces with two equivalent Mg(3)Si12 cuboctahedra. The corner-sharing octahedral tilt angles are 23°. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to two equivalent Mg(2), three equivalent Mg(1), one Si(4), and two equivalent Si(1) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(1), one Si(3), and two equivalent Si(4) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Mg(1), three equivalent Mg(3), one Si(2), one Si(4), and two equivalent Si(3) atoms. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(3), one Si(1), one Si(3), and two equivalent Si(2) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_MgSi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.638
_cell_length_b   5.638
_cell_length_c   11.137
_cell_angle_alpha   73.813
_cell_angle_beta   73.813
_cell_angle_gamma   39.421
_symmetry_Int_Tables_number   1
_cell_volume   214.688
_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
  Mg  Mg0  1  0.212  0.212  0.294  1.0
  Mg  Mg1  1  0.500  0.500  0.500  1.0
  Mg  Mg2  1  0.788  0.788  0.706  1.0
  Mg  Mg3  1  0.500  0.500  0.000  1.0
  Si  Si4  1  0.184  0.184  0.547  1.0
  Si  Si5  1  0.555  0.555  0.231  1.0
  Si  Si6  1  0.767  0.767  0.068  1.0
  Si  Si7  1  0.085  0.085  0.782  1.0
  Si  Si8  1  0.915  0.915  0.218  1.0
  Si  Si9  1  0.816  0.816  0.453  1.0
  Si  Si10  1  0.445  0.445  0.769  1.0
  Si  Si11  1  0.233  0.233  0.932  1.0
[/CIF]
.