The structure described by MgSi2 crystallizes in the monoclinic Pm space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to one Si(3), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(8) atoms. In the second Mg site, Mg(2) is bonded in a 8-coordinate geometry to two equivalent Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(6) atoms. 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 in a 5-coordinate geometry to one Si(2), two equivalent Si(3), two equivalent Si(5), and two equivalent Si(8) atoms. 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 8-coordinate geometry to one Mg(4), 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 6-coordinate geometry to one Mg(1), 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 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), 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 7-coordinate geometry to two equivalent 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   3.710
_cell_length_b   5.310
_cell_length_c   12.160
_cell_angle_alpha   77.913
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   234.207
_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  0.000  0.252  0.202  1.0
  Mg  Mg1  1  0.500  0.629  0.955  1.0
  Mg  Mg2  1  0.000  0.003  0.714  1.0
  Mg  Mg3  1  0.500  0.708  0.301  1.0
  Si  Si4  1  0.500  0.176  0.860  1.0
  Si  Si5  1  0.500  0.070  0.061  1.0
  Si  Si6  1  0.000  0.386  0.432  1.0
  Si  Si7  1  0.500  0.843  0.572  1.0
  Si  Si8  1  0.000  0.778  0.112  1.0
  Si  Si9  1  0.000  0.455  0.800  1.0
  Si  Si10  1  0.000  0.564  0.596  1.0
  Si  Si11  1  0.500  0.137  0.396  1.0
[/CIF]
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The structure described by MgSi2 crystallizes in the monoclinic Pm space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to one Si(3), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(8) atoms. In the second Mg site, Mg(2) is bonded in a 8-coordinate geometry to two equivalent Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(6) atoms. 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 in a 5-coordinate geometry to one Si(2), two equivalent Si(3), two equivalent Si(5), and two equivalent Si(8) atoms. 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 8-coordinate geometry to one Mg(4), 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 6-coordinate geometry to one Mg(1), 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 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), 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 7-coordinate geometry to two equivalent 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   3.710
_cell_length_b   5.310
_cell_length_c   12.160
_cell_angle_alpha   77.913
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   234.207
_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  0.000  0.252  0.202  1.0
  Mg  Mg1  1  0.500  0.629  0.955  1.0
  Mg  Mg2  1  0.000  0.003  0.714  1.0
  Mg  Mg3  1  0.500  0.708  0.301  1.0
  Si  Si4  1  0.500  0.176  0.860  1.0
  Si  Si5  1  0.500  0.070  0.061  1.0
  Si  Si6  1  0.000  0.386  0.432  1.0
  Si  Si7  1  0.500  0.843  0.572  1.0
  Si  Si8  1  0.000  0.778  0.112  1.0
  Si  Si9  1  0.000  0.455  0.800  1.0
  Si  Si10  1  0.000  0.564  0.596  1.0
  Si  Si11  1  0.500  0.137  0.396  1.0
[/CIF]
.