The structure described by MgSi2 crystallizes in the triclinic P-1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(1), one Si(2), one Si(5), one Si(7), and one Si(8) atom to form distorted MgSi5 tetrahedra that share corners with three equivalent Si(6)Si4 tetrahedra and corners with two equivalent Si(4)Mg2Si3 trigonal bipyramids. In the second Mg site, Mg(2) is bonded in a 3-coordinate geometry to two equivalent Si(2), two equivalent Si(3), and two equivalent Si(5) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(1), one Si(2), one Si(3), one Si(4), one Si(5), and one Si(7) atom. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(4), one Si(5), one Si(8), two equivalent Si(2), and two equivalent Si(3) atoms. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(3), one Si(1), one Si(4), and one Si(6) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(3), two equivalent Mg(2), two equivalent Mg(4), one Si(3), and one Si(7) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(3), two equivalent Mg(2), two equivalent Mg(4), one Si(2), one Si(3), and one Si(5) atom. In the fourth Si site, Si(4) is bonded to one Mg(3), one Mg(4), one Si(1), one Si(6), and one Si(7) atom to form distorted SiMg2Si3 trigonal bipyramids that share corners with two equivalent Mg(1)Si5 tetrahedra and corners with two equivalent Si(6)Si4 tetrahedra. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(3), one Mg(4), two equivalent Mg(2), one Si(3), and one Si(8) atom. In the sixth Si site, Si(6) is bonded to one Si(1), one Si(4), one Si(7), and one Si(8) atom to form distorted SiSi4 tetrahedra that share corners with three equivalent Mg(1)Si5 tetrahedra and corners with two equivalent Si(4)Mg2Si3 trigonal bipyramids. In the seventh Si site, Si(7) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(3), one Si(2), one Si(4), one Si(6), and one Si(8) atom. In the eighth Si site, Si(8) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(4), one Si(5), one Si(6), and one Si(7) atom. is represented by the CIF card [CIF]
data_MgSi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.542
_cell_length_b   6.859
_cell_length_c   10.665
_cell_angle_alpha   94.147
_cell_angle_beta   89.495
_cell_angle_gamma   100.151
_symmetry_Int_Tables_number   1
_cell_volume   469.815
_cell_formula_units_Z   8
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  0.258  0.160  0.262  1.0
  Mg  Mg1  1  0.742  0.840  0.738  1.0
  Mg  Mg2  1  0.780  0.597  0.984  1.0
  Mg  Mg3  1  0.590  0.350  0.737  1.0
  Mg  Mg4  1  0.793  0.018  0.144  1.0
  Mg  Mg5  1  0.207  0.982  0.856  1.0
  Mg  Mg6  1  0.410  0.650  0.263  1.0
  Mg  Mg7  1  0.220  0.403  0.016  1.0
  Si  Si8  1  0.458  0.326  0.471  1.0
  Si  Si9  1  0.884  0.187  0.877  1.0
  Si  Si10  1  0.446  0.819  0.019  1.0
  Si  Si11  1  0.272  0.119  0.620  1.0
  Si  Si12  1  0.618  0.370  0.174  1.0
  Si  Si13  1  0.219  0.786  0.533  1.0
  Si  Si14  1  0.728  0.881  0.381  1.0
  Si  Si15  1  0.977  0.268  0.660  1.0
  Si  Si16  1  0.116  0.813  0.123  1.0
  Si  Si17  1  0.781  0.214  0.467  1.0
  Si  Si18  1  0.023  0.732  0.340  1.0
  Si  Si19  1  0.382  0.630  0.826  1.0
  Si  Si20  1  0.940  0.383  0.292  1.0
  Si  Si21  1  0.554  0.181  0.981  1.0
  Si  Si22  1  0.060  0.617  0.708  1.0
  Si  Si23  1  0.542  0.674  0.529  1.0
[/CIF]
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The structure described by MgSi2 crystallizes in the triclinic P-1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(1), one Si(2), one Si(5), one Si(7), and one Si(8) atom to form distorted MgSi5 tetrahedra that share corners with three equivalent Si(6)Si4 tetrahedra and corners with two equivalent Si(4)Mg2Si3 trigonal bipyramids. In the second Mg site, Mg(2) is bonded in a 3-coordinate geometry to two equivalent Si(2), two equivalent Si(3), and two equivalent Si(5) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(1), one Si(2), one Si(3), one Si(4), one Si(5), and one Si(7) atom. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(4), one Si(5), one Si(8), two equivalent Si(2), and two equivalent Si(3) atoms. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(3), one Si(1), one Si(4), and one Si(6) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(3), two equivalent Mg(2), two equivalent Mg(4), one Si(3), and one Si(7) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(3), two equivalent Mg(2), two equivalent Mg(4), one Si(2), one Si(3), and one Si(5) atom. In the fourth Si site, Si(4) is bonded to one Mg(3), one Mg(4), one Si(1), one Si(6), and one Si(7) atom to form distorted SiMg2Si3 trigonal bipyramids that share corners with two equivalent Mg(1)Si5 tetrahedra and corners with two equivalent Si(6)Si4 tetrahedra. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(3), one Mg(4), two equivalent Mg(2), one Si(3), and one Si(8) atom. In the sixth Si site, Si(6) is bonded to one Si(1), one Si(4), one Si(7), and one Si(8) atom to form distorted SiSi4 tetrahedra that share corners with three equivalent Mg(1)Si5 tetrahedra and corners with two equivalent Si(4)Mg2Si3 trigonal bipyramids. In the seventh Si site, Si(7) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(3), one Si(2), one Si(4), one Si(6), and one Si(8) atom. In the eighth Si site, Si(8) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(4), one Si(5), one Si(6), and one Si(7) atom. is represented by the CIF card [CIF]
data_MgSi2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.542
_cell_length_b   6.859
_cell_length_c   10.665
_cell_angle_alpha   94.147
_cell_angle_beta   89.495
_cell_angle_gamma   100.151
_symmetry_Int_Tables_number   1
_cell_volume   469.815
_cell_formula_units_Z   8
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  0.258  0.160  0.262  1.0
  Mg  Mg1  1  0.742  0.840  0.738  1.0
  Mg  Mg2  1  0.780  0.597  0.984  1.0
  Mg  Mg3  1  0.590  0.350  0.737  1.0
  Mg  Mg4  1  0.793  0.018  0.144  1.0
  Mg  Mg5  1  0.207  0.982  0.856  1.0
  Mg  Mg6  1  0.410  0.650  0.263  1.0
  Mg  Mg7  1  0.220  0.403  0.016  1.0
  Si  Si8  1  0.458  0.326  0.471  1.0
  Si  Si9  1  0.884  0.187  0.877  1.0
  Si  Si10  1  0.446  0.819  0.019  1.0
  Si  Si11  1  0.272  0.119  0.620  1.0
  Si  Si12  1  0.618  0.370  0.174  1.0
  Si  Si13  1  0.219  0.786  0.533  1.0
  Si  Si14  1  0.728  0.881  0.381  1.0
  Si  Si15  1  0.977  0.268  0.660  1.0
  Si  Si16  1  0.116  0.813  0.123  1.0
  Si  Si17  1  0.781  0.214  0.467  1.0
  Si  Si18  1  0.023  0.732  0.340  1.0
  Si  Si19  1  0.382  0.630  0.826  1.0
  Si  Si20  1  0.940  0.383  0.292  1.0
  Si  Si21  1  0.554  0.181  0.981  1.0
  Si  Si22  1  0.060  0.617  0.708  1.0
  Si  Si23  1  0.542  0.674  0.529  1.0
[/CIF]
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