The compound 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 distorted water-like geometry to one Si(2) and two equivalent Si(6) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(2), one Si(6), two equivalent Si(3), and two equivalent Si(7) atoms. In the third Mg site, Mg(3) is bonded in a distorted single-bond geometry to one Mg(7), two equivalent Mg(8), and one Si(3) atom. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Mg(8), one Si(2), two equivalent Si(3), two equivalent Si(6), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Si(3) and two equivalent Si(2) atoms. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to one Mg(8), two equivalent Mg(7), one Si(1), one Si(4), one Si(5), and one Si(8) atom. In the seventh Mg site, Mg(7) is bonded in a 13-coordinate geometry to one Mg(11), one Mg(3), one Mg(8), two equivalent Mg(14), two equivalent Mg(6), 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 12-coordinate geometry to one Mg(4), one Mg(6), one Mg(7), two equivalent Mg(13), two equivalent Mg(14), two equivalent Mg(3), one Si(3), and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), one Si(5), and one Si(6) atom. In the tenth Mg site, Mg(10) is bonded in a 4-coordinate geometry to one Si(1), one Si(2), one Si(5), and one Si(6) atom. In the eleventh Mg site, Mg(11) is bonded in a 4-coordinate geometry to one Mg(7), one Si(4), one Si(5), one Si(8), and two equivalent Si(1) atoms. In the twelfth Mg site, Mg(12) is bonded in a 5-coordinate geometry to one Si(4), two equivalent Si(1), and two equivalent Si(5) atoms. In the thirteenth Mg site, Mg(13) is bonded in a 2-coordinate geometry to two equivalent Mg(8), one Si(4), one Si(7), and one Si(8) atom. In the fourteenth Mg site, Mg(14) is bonded in a 3-coordinate geometry to two equivalent Mg(7), two equivalent Mg(8), 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 10-coordinate geometry to one Mg(10), one Mg(6), one Mg(7), one Mg(9), 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(1), one Mg(10), one Mg(2), one Mg(4), one Mg(9), two equivalent Mg(5), one Si(3), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(3), one Mg(5), one Mg(8), two equivalent Mg(2), two equivalent Mg(4), one Si(2), and one Si(7) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(11), one Mg(12), one Mg(13), one Mg(14), one 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 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(6), one Mg(7), one Mg(9), two equivalent Mg(12), one Si(1), and one Si(4) atom. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(2), one Mg(9), two equivalent Mg(1), two equivalent Mg(4), one Si(2), and one Si(7) atom. In the seventh Si site, Si(7) is bonded in a 10-coordinate geometry to one Mg(13), one Mg(14), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(8), one Si(3), and one Si(6) atom. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(14), one Mg(6), two equivalent Mg(7), 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   5.157
_cell_length_b   5.983
_cell_length_c   14.265
_cell_angle_alpha   92.751
_cell_angle_beta   94.934
_cell_angle_gamma   96.500
_symmetry_Int_Tables_number   1
_cell_volume   434.917
_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  0.632  0.094  0.091  1.0
  Mg  Mg1  1  0.292  0.456  0.361  1.0
  Mg  Mg2  1  0.771  0.428  0.494  1.0
  Mg  Mg3  1  0.721  0.126  0.300  1.0
  Mg  Mg4  1  0.521  0.606  0.158  1.0
  Mg  Mg5  1  0.791  0.715  0.693  1.0
  Mg  Mg6  1  0.823  0.217  0.694  1.0
  Mg  Mg7  1  0.740  0.921  0.486  1.0
  Mg  Mg8  1  0.138  0.271  0.007  1.0
  Mg  Mg9  1  0.036  0.760  0.048  1.0
  Mg  Mg10  1  0.585  0.234  0.885  1.0
  Mg  Mg11  1  0.514  0.736  0.906  1.0
  Mg  Mg12  1  0.265  0.699  0.567  1.0
  Mg  Mg13  1  0.262  0.198  0.549  1.0
  Si  Si14  1  0.032  0.946  0.859  1.0
  Si  Si15  1  0.011  0.436  0.185  1.0
  Si  Si16  1  0.828  0.630  0.323  1.0
  Si  Si17  1  0.326  0.448  0.733  1.0
  Si  Si18  1  0.008  0.533  0.858  1.0
  Si  Si19  1  0.201  0.070  0.201  1.0
  Si  Si20  1  0.191  0.953  0.373  1.0
  Si  Si21  1  0.309  0.019  0.725  1.0
[/CIF]
.
The compound 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 distorted water-like geometry to one Si(2) and two equivalent Si(6) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(2), one Si(6), two equivalent Si(3), and two equivalent Si(7) atoms. In the third Mg site, Mg(3) is bonded in a distorted single-bond geometry to one Mg(7), two equivalent Mg(8), and one Si(3) atom. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Mg(8), one Si(2), two equivalent Si(3), two equivalent Si(6), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Si(3) and two equivalent Si(2) atoms. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to one Mg(8), two equivalent Mg(7), one Si(1), one Si(4), one Si(5), and one Si(8) atom. In the seventh Mg site, Mg(7) is bonded in a 13-coordinate geometry to one Mg(11), one Mg(3), one Mg(8), two equivalent Mg(14), two equivalent Mg(6), 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 12-coordinate geometry to one Mg(4), one Mg(6), one Mg(7), two equivalent Mg(13), two equivalent Mg(14), two equivalent Mg(3), one Si(3), and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), one Si(5), and one Si(6) atom. In the tenth Mg site, Mg(10) is bonded in a 4-coordinate geometry to one Si(1), one Si(2), one Si(5), and one Si(6) atom. In the eleventh Mg site, Mg(11) is bonded in a 4-coordinate geometry to one Mg(7), one Si(4), one Si(5), one Si(8), and two equivalent Si(1) atoms. In the twelfth Mg site, Mg(12) is bonded in a 5-coordinate geometry to one Si(4), two equivalent Si(1), and two equivalent Si(5) atoms. In the thirteenth Mg site, Mg(13) is bonded in a 2-coordinate geometry to two equivalent Mg(8), one Si(4), one Si(7), and one Si(8) atom. In the fourteenth Mg site, Mg(14) is bonded in a 3-coordinate geometry to two equivalent Mg(7), two equivalent Mg(8), 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 10-coordinate geometry to one Mg(10), one Mg(6), one Mg(7), one Mg(9), 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(1), one Mg(10), one Mg(2), one Mg(4), one Mg(9), two equivalent Mg(5), one Si(3), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(3), one Mg(5), one Mg(8), two equivalent Mg(2), two equivalent Mg(4), one Si(2), and one Si(7) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(11), one Mg(12), one Mg(13), one Mg(14), one 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 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(6), one Mg(7), one Mg(9), two equivalent Mg(12), one Si(1), and one Si(4) atom. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(2), one Mg(9), two equivalent Mg(1), two equivalent Mg(4), one Si(2), and one Si(7) atom. In the seventh Si site, Si(7) is bonded in a 10-coordinate geometry to one Mg(13), one Mg(14), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(8), one Si(3), and one Si(6) atom. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(14), one Mg(6), two equivalent Mg(7), 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   5.157
_cell_length_b   5.983
_cell_length_c   14.265
_cell_angle_alpha   92.751
_cell_angle_beta   94.934
_cell_angle_gamma   96.500
_symmetry_Int_Tables_number   1
_cell_volume   434.917
_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  0.632  0.094  0.091  1.0
  Mg  Mg1  1  0.292  0.456  0.361  1.0
  Mg  Mg2  1  0.771  0.428  0.494  1.0
  Mg  Mg3  1  0.721  0.126  0.300  1.0
  Mg  Mg4  1  0.521  0.606  0.158  1.0
  Mg  Mg5  1  0.791  0.715  0.693  1.0
  Mg  Mg6  1  0.823  0.217  0.694  1.0
  Mg  Mg7  1  0.740  0.921  0.486  1.0
  Mg  Mg8  1  0.138  0.271  0.007  1.0
  Mg  Mg9  1  0.036  0.760  0.048  1.0
  Mg  Mg10  1  0.585  0.234  0.885  1.0
  Mg  Mg11  1  0.514  0.736  0.906  1.0
  Mg  Mg12  1  0.265  0.699  0.567  1.0
  Mg  Mg13  1  0.262  0.198  0.549  1.0
  Si  Si14  1  0.032  0.946  0.859  1.0
  Si  Si15  1  0.011  0.436  0.185  1.0
  Si  Si16  1  0.828  0.630  0.323  1.0
  Si  Si17  1  0.326  0.448  0.733  1.0
  Si  Si18  1  0.008  0.533  0.858  1.0
  Si  Si19  1  0.201  0.070  0.201  1.0
  Si  Si20  1  0.191  0.953  0.373  1.0
  Si  Si21  1  0.309  0.019  0.725  1.0
[/CIF]
.