The crystal structure described by Mg7Si4 crystallizes in the triclinic P1 space group. There are fourteen inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 3-coordinate geometry to one Si(3), one Si(6), and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(2), one Si(6), one Si(7), and two equivalent Si(3) atoms. In the third Mg site, Mg(3) is bonded in a 3-coordinate geometry to one Si(3), one Si(6), and one Si(7) atom. In the fourth Mg site, Mg(4) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(6), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a distorted water-like geometry to one Si(2) and one Si(3) atom. In the sixth Mg site, Mg(6) is bonded in a 5-coordinate geometry to one Si(1), one Si(4), one Si(5), and two equivalent Si(8) atoms. In the seventh Mg site, Mg(7) is bonded in a 3-coordinate geometry to one Si(4), one Si(5), and one Si(8) atom. In the eighth Mg site, Mg(8) is bonded in a 2-coordinate geometry to one Si(4), one Si(7), and one Si(8) atom. In the ninth Mg site, Mg(9) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), and one Si(5) atom. In the tenth Mg site, Mg(10) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the eleventh Mg site, Mg(11) is bonded in a 3-coordinate geometry to one Si(1), one Si(4), and two equivalent Si(5) atoms. In the twelfth Mg site, Mg(12) is bonded in a 4-coordinate geometry to one Si(5), one Si(8), and two equivalent Si(1) atoms. In the thirteenth Mg site, Mg(13) is bonded in a 2-coordinate geometry to one Si(3), one Si(4), one Si(6), and one Si(7) atom. In the fourteenth Mg site, Mg(14) is bonded in a 3-coordinate geometry to one Si(4), one Si(7), and one Si(8) atom. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(10), one Mg(11), one Mg(6), one Mg(9), two equivalent Mg(12), one Si(5), and one Si(8) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(10), one Mg(2), one Mg(4), one Mg(5), one Mg(9), two equivalent Mg(1), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(3), one Mg(4), one Mg(5), two equivalent Mg(2), and one Si(6) atom. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(14), one Mg(6), one Mg(7), one Mg(8), one Si(5), and one Si(8) atom. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(12), one Mg(6), one Mg(7), one Mg(9), two equivalent Mg(11), one Si(1), and one Si(4) atom. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(2), one Mg(3), one Mg(4), one Si(2), one Si(3), and one Si(7) atom. In the seventh Si site, Si(7) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(14), one Mg(2), one Mg(3), one Mg(8), two equivalent Mg(4), and one Si(6) atom. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to one Mg(12), one Mg(14), one Mg(7), one Mg(8), two equivalent Mg(6), one Si(1), and one Si(4) atom. is represented by the CIF file [CIF]
data_Mg7Si4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.343
_cell_length_b   6.153
_cell_length_c   13.925
_cell_angle_alpha   96.561
_cell_angle_beta   96.577
_cell_angle_gamma   97.985
_symmetry_Int_Tables_number   1
_cell_volume   446.389
_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  0.278  0.828  0.867  1.0
  Mg  Mg1  1  0.861  0.264  0.760  1.0
  Mg  Mg2  1  0.589  0.048  0.558  1.0
  Mg  Mg3  1  0.367  0.511  0.664  1.0
  Mg  Mg4  1  0.396  0.344  0.882  1.0
  Mg  Mg5  1  0.198  0.538  0.259  1.0
  Mg  Mg6  1  0.402  0.033  0.327  1.0
  Mg  Mg7  1  0.515  0.540  0.447  1.0
  Mg  Mg8  1  0.970  0.536  0.004  1.0
  Mg  Mg9  1  0.827  0.039  0.953  1.0
  Mg  Mg10  1  0.523  0.748  0.105  1.0
  Mg  Mg11  1  0.364  0.218  0.084  1.0
  Mg  Mg12  1  0.065  0.796  0.492  1.0
  Mg  Mg13  1  0.975  0.252  0.420  1.0
  Si  Si14  1  0.875  0.222  0.136  1.0
  Si  Si15  1  0.753  0.665  0.833  1.0
  Si  Si16  1  0.291  0.052  0.706  1.0
  Si  Si17  1  0.804  0.800  0.303  1.0
  Si  Si18  1  0.036  0.878  0.156  1.0
  Si  Si19  1  0.881  0.825  0.690  1.0
  Si  Si20  1  0.853  0.469  0.591  1.0
  Si  Si21  1  0.676  0.401  0.267  1.0
[/CIF]
.
The crystal structure described by Mg7Si4 crystallizes in the triclinic P1 space group. There are fourteen inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 3-coordinate geometry to one Si(3), one Si(6), and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(2), one Si(6), one Si(7), and two equivalent Si(3) atoms. In the third Mg site, Mg(3) is bonded in a 3-coordinate geometry to one Si(3), one Si(6), and one Si(7) atom. In the fourth Mg site, Mg(4) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(6), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a distorted water-like geometry to one Si(2) and one Si(3) atom. In the sixth Mg site, Mg(6) is bonded in a 5-coordinate geometry to one Si(1), one Si(4), one Si(5), and two equivalent Si(8) atoms. In the seventh Mg site, Mg(7) is bonded in a 3-coordinate geometry to one Si(4), one Si(5), and one Si(8) atom. In the eighth Mg site, Mg(8) is bonded in a 2-coordinate geometry to one Si(4), one Si(7), and one Si(8) atom. In the ninth Mg site, Mg(9) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), and one Si(5) atom. In the tenth Mg site, Mg(10) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the eleventh Mg site, Mg(11) is bonded in a 3-coordinate geometry to one Si(1), one Si(4), and two equivalent Si(5) atoms. In the twelfth Mg site, Mg(12) is bonded in a 4-coordinate geometry to one Si(5), one Si(8), and two equivalent Si(1) atoms. In the thirteenth Mg site, Mg(13) is bonded in a 2-coordinate geometry to one Si(3), one Si(4), one Si(6), and one Si(7) atom. In the fourteenth Mg site, Mg(14) is bonded in a 3-coordinate geometry to one Si(4), one Si(7), and one Si(8) atom. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(10), one Mg(11), one Mg(6), one Mg(9), two equivalent Mg(12), one Si(5), and one Si(8) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(10), one Mg(2), one Mg(4), one Mg(5), one Mg(9), two equivalent Mg(1), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(3), one Mg(4), one Mg(5), two equivalent Mg(2), and one Si(6) atom. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(14), one Mg(6), one Mg(7), one Mg(8), one Si(5), and one Si(8) atom. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(12), one Mg(6), one Mg(7), one Mg(9), two equivalent Mg(11), one Si(1), and one Si(4) atom. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(2), one Mg(3), one Mg(4), one Si(2), one Si(3), and one Si(7) atom. In the seventh Si site, Si(7) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(14), one Mg(2), one Mg(3), one Mg(8), two equivalent Mg(4), and one Si(6) atom. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to one Mg(12), one Mg(14), one Mg(7), one Mg(8), two equivalent Mg(6), one Si(1), and one Si(4) atom. is represented by the CIF file [CIF]
data_Mg7Si4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.343
_cell_length_b   6.153
_cell_length_c   13.925
_cell_angle_alpha   96.561
_cell_angle_beta   96.577
_cell_angle_gamma   97.985
_symmetry_Int_Tables_number   1
_cell_volume   446.389
_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  0.278  0.828  0.867  1.0
  Mg  Mg1  1  0.861  0.264  0.760  1.0
  Mg  Mg2  1  0.589  0.048  0.558  1.0
  Mg  Mg3  1  0.367  0.511  0.664  1.0
  Mg  Mg4  1  0.396  0.344  0.882  1.0
  Mg  Mg5  1  0.198  0.538  0.259  1.0
  Mg  Mg6  1  0.402  0.033  0.327  1.0
  Mg  Mg7  1  0.515  0.540  0.447  1.0
  Mg  Mg8  1  0.970  0.536  0.004  1.0
  Mg  Mg9  1  0.827  0.039  0.953  1.0
  Mg  Mg10  1  0.523  0.748  0.105  1.0
  Mg  Mg11  1  0.364  0.218  0.084  1.0
  Mg  Mg12  1  0.065  0.796  0.492  1.0
  Mg  Mg13  1  0.975  0.252  0.420  1.0
  Si  Si14  1  0.875  0.222  0.136  1.0
  Si  Si15  1  0.753  0.665  0.833  1.0
  Si  Si16  1  0.291  0.052  0.706  1.0
  Si  Si17  1  0.804  0.800  0.303  1.0
  Si  Si18  1  0.036  0.878  0.156  1.0
  Si  Si19  1  0.881  0.825  0.690  1.0
  Si  Si20  1  0.853  0.469  0.591  1.0
  Si  Si21  1  0.676  0.401  0.267  1.0
[/CIF]
.