The structure described by MgSi2 crystallizes in the monoclinic Cm space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(8), two equivalent Si(2), and two equivalent Si(5) atoms. In the second Mg site, Mg(2) is bonded to two equivalent Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(6) atoms to form MgSi8 hexagonal bipyramids that share corners with two equivalent Mg(4)Si5 tetrahedra, edges with four equivalent Mg(2)Si8 hexagonal bipyramids, and edges with four equivalent Mg(3)Si8 hexagonal bipyramids. In the third Mg site, Mg(3) is bonded to two equivalent Si(1), two equivalent Si(4), two equivalent Si(6), and two equivalent Si(7) atoms to form distorted edge-sharing MgSi8 hexagonal bipyramids. In the fourth Mg site, Mg(4) is bonded to one Si(5), two equivalent Si(3), and two equivalent Si(8) atoms to form distorted MgSi5 tetrahedra that share corners with two equivalent Mg(2)Si8 hexagonal bipyramids and corners with four equivalent Mg(4)Si5 tetrahedra. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), one Si(2), and two equivalent Si(6) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), one Si(1), and two equivalent Si(5) atoms. In the third Si site, Si(3) is bonded in a 5-coordinate geometry to two equivalent Mg(4), one Si(7), and two equivalent Si(8) atoms. In the fourth Si site, Si(4) is bonded in a 5-coordinate geometry to two equivalent Mg(3), one Si(8), and two equivalent Si(7) atoms. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Mg(4), two equivalent Mg(1), two equivalent Mg(2), and two equivalent Si(2) atoms. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), one Si(7), and two equivalent Si(1) atoms. In the seventh Si site, Si(7) is bonded in a distorted hexagonal planar geometry to two equivalent Mg(3), one Si(3), one Si(6), and two equivalent Si(4) atoms. In the eighth Si site, Si(8) is bonded in a 6-coordinate geometry to one Mg(1), two equivalent Mg(4), one Si(4), and two equivalent Si(3) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_MgSi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   12.390
_cell_length_b   12.390
_cell_length_c   5.387
_cell_angle_alpha   77.798
_cell_angle_beta   77.798
_cell_angle_gamma   17.368
_symmetry_Int_Tables_number   1
_cell_volume   241.145
_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  0.203  0.203  0.723  1.0
  Mg  Mg1  1  0.819  0.819  0.367  1.0
  Mg  Mg2  1  0.431  0.431  0.020  1.0
  Mg  Mg3  1  0.129  0.129  0.282  1.0
  Si  Si4  1  0.862  0.862  0.828  1.0
  Si  Si5  1  0.763  0.763  0.935  1.0
  Si  Si6  1  0.575  0.575  0.612  1.0
  Si  Si7  1  0.003  0.003  0.167  1.0
  Si  Si8  1  0.241  0.241  0.213  1.0
  Si  Si9  1  0.393  0.393  0.560  1.0
  Si  Si10  1  0.494  0.494  0.439  1.0
  Si  Si11  1  0.088  0.088  0.854  1.0
[/CIF]
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The structure described by MgSi2 crystallizes in the monoclinic Cm space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(8), two equivalent Si(2), and two equivalent Si(5) atoms. In the second Mg site, Mg(2) is bonded to two equivalent Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(6) atoms to form MgSi8 hexagonal bipyramids that share corners with two equivalent Mg(4)Si5 tetrahedra, edges with four equivalent Mg(2)Si8 hexagonal bipyramids, and edges with four equivalent Mg(3)Si8 hexagonal bipyramids. In the third Mg site, Mg(3) is bonded to two equivalent Si(1), two equivalent Si(4), two equivalent Si(6), and two equivalent Si(7) atoms to form distorted edge-sharing MgSi8 hexagonal bipyramids. In the fourth Mg site, Mg(4) is bonded to one Si(5), two equivalent Si(3), and two equivalent Si(8) atoms to form distorted MgSi5 tetrahedra that share corners with two equivalent Mg(2)Si8 hexagonal bipyramids and corners with four equivalent Mg(4)Si5 tetrahedra. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), one Si(2), and two equivalent Si(6) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), one Si(1), and two equivalent Si(5) atoms. In the third Si site, Si(3) is bonded in a 5-coordinate geometry to two equivalent Mg(4), one Si(7), and two equivalent Si(8) atoms. In the fourth Si site, Si(4) is bonded in a 5-coordinate geometry to two equivalent Mg(3), one Si(8), and two equivalent Si(7) atoms. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Mg(4), two equivalent Mg(1), two equivalent Mg(2), and two equivalent Si(2) atoms. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), one Si(7), and two equivalent Si(1) atoms. In the seventh Si site, Si(7) is bonded in a distorted hexagonal planar geometry to two equivalent Mg(3), one Si(3), one Si(6), and two equivalent Si(4) atoms. In the eighth Si site, Si(8) is bonded in a 6-coordinate geometry to one Mg(1), two equivalent Mg(4), one Si(4), and two equivalent Si(3) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_MgSi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   12.390
_cell_length_b   12.390
_cell_length_c   5.387
_cell_angle_alpha   77.798
_cell_angle_beta   77.798
_cell_angle_gamma   17.368
_symmetry_Int_Tables_number   1
_cell_volume   241.145
_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  0.203  0.203  0.723  1.0
  Mg  Mg1  1  0.819  0.819  0.367  1.0
  Mg  Mg2  1  0.431  0.431  0.020  1.0
  Mg  Mg3  1  0.129  0.129  0.282  1.0
  Si  Si4  1  0.862  0.862  0.828  1.0
  Si  Si5  1  0.763  0.763  0.935  1.0
  Si  Si6  1  0.575  0.575  0.612  1.0
  Si  Si7  1  0.003  0.003  0.167  1.0
  Si  Si8  1  0.241  0.241  0.213  1.0
  Si  Si9  1  0.393  0.393  0.560  1.0
  Si  Si10  1  0.494  0.494  0.439  1.0
  Si  Si11  1  0.088  0.088  0.854  1.0
[/CIF]
.