The 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 2-coordinate geometry to one Si(3) and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one Si(2), one Si(6), and two equivalent Si(3) atoms. In the third Mg site, Mg(3) is bonded in a 3-coordinate geometry to one Si(3) and two equivalent Si(7) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(3), two equivalent Si(2), two equivalent Si(6), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a distorted water-like geometry to two equivalent Si(2) atoms. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to two equivalent Si(4) and two equivalent Si(8) atoms. In the seventh Mg site, Mg(7) is bonded in a 6-coordinate geometry to one Si(1), one Si(5), two equivalent Si(4), and two equivalent Si(8) atoms. In the eighth Mg site, Mg(8) is bonded in a 3-coordinate geometry to one Si(3) and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a distorted linear geometry to one Si(2) and one Si(5) atom. In the tenth Mg site, Mg(10) is bonded in a distorted single-bond geometry to one Si(1) atom. In the eleventh Mg site, Mg(11) is bonded in a 4-coordinate geometry to two equivalent Si(1) and two equivalent Si(5) atoms. In the twelfth Mg site, Mg(12) is bonded in a 6-coordinate geometry to one Si(4), one Si(8), two equivalent Si(1), and two equivalent Si(5) atoms. In the thirteenth Mg site, Mg(13) is bonded in a distorted single-bond geometry to one Si(4) atom. In the fourteenth Mg site, Mg(14) is bonded in a distorted linear geometry to 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(7), two equivalent Mg(11), two equivalent Mg(12), one Si(5), and one Si(8) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(9), two equivalent Mg(1), two equivalent Mg(4), two equivalent Mg(5), 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(3), one Mg(4), one Mg(8), two equivalent Mg(2), and two equivalent Si(6) atoms. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to one Mg(12), one Mg(13), two equivalent Mg(6), two equivalent Mg(7), 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(7), one Mg(9), two equivalent Mg(11), two equivalent Mg(12), one Si(1), and one Si(4) atom. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(2), two equivalent Mg(4), one Si(2), one Si(7), and two equivalent Si(3) atoms. In the seventh Si site, Si(7) is bonded in a 8-coordinate geometry to one Mg(14), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(8), 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), two equivalent Mg(6), two equivalent Mg(7), one Si(1), and one Si(4) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg7Si4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.288
_cell_length_b   6.254
_cell_length_c   16.847
_cell_angle_alpha   99.016
_cell_angle_beta   93.767
_cell_angle_gamma   89.795
_symmetry_Int_Tables_number   1
_cell_volume   445.210
_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  0.426  0.860  0.862  1.0
  Mg  Mg1  1  0.905  0.129  0.776  1.0
  Mg  Mg2  1  0.346  0.107  0.536  1.0
  Mg  Mg3  1  0.387  0.402  0.703  1.0
  Mg  Mg4  1  0.431  0.379  0.888  1.0
  Mg  Mg5  1  0.284  0.546  0.336  1.0
  Mg  Mg6  1  0.289  0.029  0.297  1.0
  Mg  Mg7  1  0.347  0.609  0.536  1.0
  Mg  Mg8  1  0.962  0.659  0.979  1.0
  Mg  Mg9  1  0.955  0.158  0.973  1.0
  Mg  Mg10  1  0.486  0.944  0.070  1.0
  Mg  Mg11  1  0.479  0.464  0.107  1.0
  Mg  Mg12  1  0.816  0.831  0.433  1.0
  Mg  Mg13  1  0.815  0.314  0.427  1.0
  Si  Si14  1  0.002  0.168  0.140  1.0
  Si  Si15  1  0.916  0.568  0.812  1.0
  Si  Si16  1  0.380  0.925  0.678  1.0
  Si  Si17  1  0.767  0.720  0.267  1.0
  Si  Si18  1  0.004  0.776  0.145  1.0
  Si  Si19  1  0.883  0.720  0.685  1.0
  Si  Si20  1  0.859  0.378  0.592  1.0
  Si  Si21  1  0.759  0.323  0.261  1.0
[/CIF]
.
The 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 2-coordinate geometry to one Si(3) and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one Si(2), one Si(6), and two equivalent Si(3) atoms. In the third Mg site, Mg(3) is bonded in a 3-coordinate geometry to one Si(3) and two equivalent Si(7) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(3), two equivalent Si(2), two equivalent Si(6), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a distorted water-like geometry to two equivalent Si(2) atoms. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to two equivalent Si(4) and two equivalent Si(8) atoms. In the seventh Mg site, Mg(7) is bonded in a 6-coordinate geometry to one Si(1), one Si(5), two equivalent Si(4), and two equivalent Si(8) atoms. In the eighth Mg site, Mg(8) is bonded in a 3-coordinate geometry to one Si(3) and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a distorted linear geometry to one Si(2) and one Si(5) atom. In the tenth Mg site, Mg(10) is bonded in a distorted single-bond geometry to one Si(1) atom. In the eleventh Mg site, Mg(11) is bonded in a 4-coordinate geometry to two equivalent Si(1) and two equivalent Si(5) atoms. In the twelfth Mg site, Mg(12) is bonded in a 6-coordinate geometry to one Si(4), one Si(8), two equivalent Si(1), and two equivalent Si(5) atoms. In the thirteenth Mg site, Mg(13) is bonded in a distorted single-bond geometry to one Si(4) atom. In the fourteenth Mg site, Mg(14) is bonded in a distorted linear geometry to 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(7), two equivalent Mg(11), two equivalent Mg(12), one Si(5), and one Si(8) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(9), two equivalent Mg(1), two equivalent Mg(4), two equivalent Mg(5), 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(3), one Mg(4), one Mg(8), two equivalent Mg(2), and two equivalent Si(6) atoms. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to one Mg(12), one Mg(13), two equivalent Mg(6), two equivalent Mg(7), 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(7), one Mg(9), two equivalent Mg(11), two equivalent Mg(12), one Si(1), and one Si(4) atom. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(2), two equivalent Mg(4), one Si(2), one Si(7), and two equivalent Si(3) atoms. In the seventh Si site, Si(7) is bonded in a 8-coordinate geometry to one Mg(14), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(8), 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), two equivalent Mg(6), two equivalent Mg(7), one Si(1), and one Si(4) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg7Si4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.288
_cell_length_b   6.254
_cell_length_c   16.847
_cell_angle_alpha   99.016
_cell_angle_beta   93.767
_cell_angle_gamma   89.795
_symmetry_Int_Tables_number   1
_cell_volume   445.210
_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  0.426  0.860  0.862  1.0
  Mg  Mg1  1  0.905  0.129  0.776  1.0
  Mg  Mg2  1  0.346  0.107  0.536  1.0
  Mg  Mg3  1  0.387  0.402  0.703  1.0
  Mg  Mg4  1  0.431  0.379  0.888  1.0
  Mg  Mg5  1  0.284  0.546  0.336  1.0
  Mg  Mg6  1  0.289  0.029  0.297  1.0
  Mg  Mg7  1  0.347  0.609  0.536  1.0
  Mg  Mg8  1  0.962  0.659  0.979  1.0
  Mg  Mg9  1  0.955  0.158  0.973  1.0
  Mg  Mg10  1  0.486  0.944  0.070  1.0
  Mg  Mg11  1  0.479  0.464  0.107  1.0
  Mg  Mg12  1  0.816  0.831  0.433  1.0
  Mg  Mg13  1  0.815  0.314  0.427  1.0
  Si  Si14  1  0.002  0.168  0.140  1.0
  Si  Si15  1  0.916  0.568  0.812  1.0
  Si  Si16  1  0.380  0.925  0.678  1.0
  Si  Si17  1  0.767  0.720  0.267  1.0
  Si  Si18  1  0.004  0.776  0.145  1.0
  Si  Si19  1  0.883  0.720  0.685  1.0
  Si  Si20  1  0.859  0.378  0.592  1.0
  Si  Si21  1  0.759  0.323  0.261  1.0
[/CIF]
.