The crystal structure described by Mg6Si5 crystallizes in the triclinic P1 space group. There are twelve inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(7), one Si(9), and two equivalent Si(4) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one Si(1), one Si(4), one Si(5), and two equivalent Si(6) atoms. In the third Mg site, Mg(3) is bonded in a 7-coordinate geometry to one Si(3), one Si(8), two equivalent Si(10), two equivalent Si(2), and two equivalent Si(6) atoms. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(5), one Si(9), and two equivalent Si(4) atoms. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Si(4), one Si(8), one Si(9), and two equivalent Si(1) atoms. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), and two equivalent Si(3) atoms. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), two equivalent Si(10), and two equivalent Si(7) atoms. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(5), one Si(6), two equivalent Si(1), and two equivalent Si(2) atoms. In the ninth Mg site, Mg(9) is bonded in a 3-coordinate geometry to one Si(1), two equivalent Si(5), and two equivalent Si(9) atoms. In the tenth Mg site, Mg(10) is bonded in a 5-coordinate geometry to one Si(9), two equivalent Si(3), and two equivalent Si(7) atoms. In the eleventh Mg site, Mg(11) is bonded in a 2-coordinate geometry to two equivalent Si(10) and two equivalent Si(7) atoms. In the twelfth Mg site, Mg(12) is bonded in a distorted trigonal non-coplanar geometry to one Si(3) and two equivalent Si(9) atoms. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(7), one Mg(9), two equivalent Mg(5), two equivalent Mg(8), and two equivalent Si(8) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(6), one Mg(7), two equivalent Mg(3), two equivalent Mg(8), one Si(6), and two equivalent Si(3) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(12), one Mg(3), two equivalent Mg(10), two equivalent Mg(6), one Si(7), and two equivalent Si(2) atoms. In the fourth Si site, Si(4) is bonded in a 6-coordinate geometry to one Mg(2), one Mg(5), two equivalent Mg(1), two equivalent Mg(4), and one Si(5) atom. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(4), one Mg(8), two equivalent Mg(9), one Si(4), and one Si(6) atom. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(8), two equivalent Mg(2), two equivalent Mg(3), one Si(2), one Si(5), and one Si(8) atom. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(10), two equivalent Mg(11), two equivalent Mg(7), one Si(10), and one Si(3) atom. In the eighth Si site, Si(8) is bonded in a 5-coordinate geometry to one Mg(3), one Mg(5), one Si(10), one Si(6), and two equivalent Si(1) atoms. In the ninth Si site, Si(9) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(10), one Mg(4), one Mg(5), two equivalent Mg(12), and two equivalent Mg(9) atoms. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(6), two equivalent Mg(11), two equivalent Mg(3), two equivalent Mg(7), one Si(7), and one Si(8) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg6Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.309
_cell_length_b   8.518
_cell_length_c   12.057
_cell_angle_alpha   79.077
_cell_angle_beta   83.157
_cell_angle_gamma   79.557
_symmetry_Int_Tables_number   1
_cell_volume   425.692
_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  0.018  0.366  0.902  1.0
  Mg  Mg1  1  0.098  0.616  0.656  1.0
  Mg  Mg2  1  0.105  0.731  0.374  1.0
  Mg  Mg3  1  0.866  0.743  0.914  1.0
  Mg  Mg4  1  0.619  0.334  0.711  1.0
  Mg  Mg5  1  0.648  0.857  0.171  1.0
  Mg  Mg6  1  0.328  0.328  0.333  1.0
  Mg  Mg7  1  0.841  0.091  0.503  1.0
  Mg  Mg8  1  0.146  0.049  0.731  1.0
  Mg  Mg9  1  0.520  0.222  0.078  1.0
  Mg  Mg10  1  0.317  0.600  0.103  1.0
  Mg  Mg11  1  0.165  0.978  0.007  1.0
  Si  Si12  1  0.187  0.332  0.560  1.0
  Si  Si13  1  0.478  0.995  0.362  1.0
  Si  Si14  1  0.032  0.061  0.232  1.0
  Si  Si15  1  0.465  0.583  0.836  1.0
  Si  Si16  1  0.626  0.836  0.699  1.0
  Si  Si17  1  0.533  0.779  0.520  1.0
  Si  Si18  1  0.936  0.358  0.160  1.0
  Si  Si19  1  0.686  0.493  0.485  1.0
  Si  Si20  1  0.661  0.091  0.887  1.0
  Si  Si21  1  0.721  0.557  0.282  1.0
[/CIF]
.
The crystal structure described by Mg6Si5 crystallizes in the triclinic P1 space group. There are twelve inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(7), one Si(9), and two equivalent Si(4) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one Si(1), one Si(4), one Si(5), and two equivalent Si(6) atoms. In the third Mg site, Mg(3) is bonded in a 7-coordinate geometry to one Si(3), one Si(8), two equivalent Si(10), two equivalent Si(2), and two equivalent Si(6) atoms. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(5), one Si(9), and two equivalent Si(4) atoms. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Si(4), one Si(8), one Si(9), and two equivalent Si(1) atoms. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), and two equivalent Si(3) atoms. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), two equivalent Si(10), and two equivalent Si(7) atoms. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(5), one Si(6), two equivalent Si(1), and two equivalent Si(2) atoms. In the ninth Mg site, Mg(9) is bonded in a 3-coordinate geometry to one Si(1), two equivalent Si(5), and two equivalent Si(9) atoms. In the tenth Mg site, Mg(10) is bonded in a 5-coordinate geometry to one Si(9), two equivalent Si(3), and two equivalent Si(7) atoms. In the eleventh Mg site, Mg(11) is bonded in a 2-coordinate geometry to two equivalent Si(10) and two equivalent Si(7) atoms. In the twelfth Mg site, Mg(12) is bonded in a distorted trigonal non-coplanar geometry to one Si(3) and two equivalent Si(9) atoms. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(7), one Mg(9), two equivalent Mg(5), two equivalent Mg(8), and two equivalent Si(8) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(6), one Mg(7), two equivalent Mg(3), two equivalent Mg(8), one Si(6), and two equivalent Si(3) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(12), one Mg(3), two equivalent Mg(10), two equivalent Mg(6), one Si(7), and two equivalent Si(2) atoms. In the fourth Si site, Si(4) is bonded in a 6-coordinate geometry to one Mg(2), one Mg(5), two equivalent Mg(1), two equivalent Mg(4), and one Si(5) atom. In the fifth Si site, Si(5) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(4), one Mg(8), two equivalent Mg(9), one Si(4), and one Si(6) atom. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(8), two equivalent Mg(2), two equivalent Mg(3), one Si(2), one Si(5), and one Si(8) atom. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(10), two equivalent Mg(11), two equivalent Mg(7), one Si(10), and one Si(3) atom. In the eighth Si site, Si(8) is bonded in a 5-coordinate geometry to one Mg(3), one Mg(5), one Si(10), one Si(6), and two equivalent Si(1) atoms. In the ninth Si site, Si(9) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(10), one Mg(4), one Mg(5), two equivalent Mg(12), and two equivalent Mg(9) atoms. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(6), two equivalent Mg(11), two equivalent Mg(3), two equivalent Mg(7), one Si(7), and one Si(8) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Mg6Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.309
_cell_length_b   8.518
_cell_length_c   12.057
_cell_angle_alpha   79.077
_cell_angle_beta   83.157
_cell_angle_gamma   79.557
_symmetry_Int_Tables_number   1
_cell_volume   425.692
_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  0.018  0.366  0.902  1.0
  Mg  Mg1  1  0.098  0.616  0.656  1.0
  Mg  Mg2  1  0.105  0.731  0.374  1.0
  Mg  Mg3  1  0.866  0.743  0.914  1.0
  Mg  Mg4  1  0.619  0.334  0.711  1.0
  Mg  Mg5  1  0.648  0.857  0.171  1.0
  Mg  Mg6  1  0.328  0.328  0.333  1.0
  Mg  Mg7  1  0.841  0.091  0.503  1.0
  Mg  Mg8  1  0.146  0.049  0.731  1.0
  Mg  Mg9  1  0.520  0.222  0.078  1.0
  Mg  Mg10  1  0.317  0.600  0.103  1.0
  Mg  Mg11  1  0.165  0.978  0.007  1.0
  Si  Si12  1  0.187  0.332  0.560  1.0
  Si  Si13  1  0.478  0.995  0.362  1.0
  Si  Si14  1  0.032  0.061  0.232  1.0
  Si  Si15  1  0.465  0.583  0.836  1.0
  Si  Si16  1  0.626  0.836  0.699  1.0
  Si  Si17  1  0.533  0.779  0.520  1.0
  Si  Si18  1  0.936  0.358  0.160  1.0
  Si  Si19  1  0.686  0.493  0.485  1.0
  Si  Si20  1  0.661  0.091  0.887  1.0
  Si  Si21  1  0.721  0.557  0.282  1.0
[/CIF]
.