The structure described by Mg9Si5 crystallizes in the triclinic P1 space group. There are eighteen inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(3), one Si(4), one Si(6), and one Si(8) atom. In the second Mg site, Mg(2) is bonded in a 3-coordinate geometry to one Si(2), one Si(6), and one Si(9) atom. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to one Si(4), one Si(6), one Si(8), and one Si(9) atom. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), and one Si(9) atom. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Si(3), one Si(8), and one Si(9) atom. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to one Si(10), one Si(3), one Si(6), and one Si(9) atom. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. In the eighth Mg site, Mg(8) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the ninth Mg site, Mg(9) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. In the tenth Mg site, Mg(10) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the eleventh Mg site, Mg(11) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. In the twelfth Mg site, Mg(12) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the thirteenth Mg site, Mg(13) is bonded in a 4-coordinate geometry to one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the fourteenth Mg site, Mg(14) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the sixteenth Mg site, Mg(16) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the seventeenth Mg site, Mg(17) is bonded to one Si(10), one Si(2), one Si(3), and one Si(5) atom to form distorted corner-sharing MgSi4 tetrahedra. In the eighteenth Mg site, Mg(18) is bonded in a distorted trigonal non-coplanar geometry to one Si(4), one Si(7), and one Si(8) atom. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(7), one Mg(8), one Mg(9), and one Si(4) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(4), one Mg(7), and one Mg(9) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(17), one Mg(4), one Mg(5), one Mg(6), and one Si(6) atom. In the fourth Si site, Si(4) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(3), and one Si(1) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(13), one Mg(15), one Mg(17), one Mg(7), one Mg(8), and one Mg(9) atom. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(2), one Mg(3), one Mg(6), and one Si(3) atom. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(7), one Mg(8), and one Mg(9) atom. In the eighth Si site, Si(8) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(10), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(3), one Mg(5), and one Mg(8) atom. In the ninth Si site, Si(9) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(15), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and one Si(10) atom. In the tenth Si site, Si(10) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(15), one Mg(17), one Mg(4), one Mg(6), one Mg(7), one Mg(9), and one Si(9) atom. is represented by the CIF file [CIF]
data_Mg9Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.255
_cell_length_b   7.267
_cell_length_c   12.397
_cell_angle_alpha   101.986
_cell_angle_beta   84.784
_cell_angle_gamma   118.865
_symmetry_Int_Tables_number   1
_cell_volume   559.870
_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  0.215  0.014  0.296  1.0
  Mg  Mg1  1  0.890  0.772  0.465  1.0
  Mg  Mg2  1  0.659  0.820  0.293  1.0
  Mg  Mg3  1  0.317  0.057  0.534  1.0
  Mg  Mg4  1  0.210  0.629  0.366  1.0
  Mg  Mg5  1  0.815  0.282  0.453  1.0
  Mg  Mg6  1  0.684  0.970  0.819  1.0
  Mg  Mg7  1  0.297  0.889  0.988  1.0
  Mg  Mg8  1  0.336  0.186  0.818  1.0
  Mg  Mg9  1  0.591  0.660  0.993  1.0
  Mg  Mg10  1  0.909  0.561  0.823  1.0
  Mg  Mg11  1  0.059  0.363  0.986  1.0
  Mg  Mg12  1  0.248  0.695  0.639  1.0
  Mg  Mg13  1  0.653  0.134  0.172  1.0
  Mg  Mg14  1  0.573  0.537  0.633  1.0
  Mg  Mg15  1  0.369  0.351  0.155  1.0
  Mg  Mg16  1  0.037  0.231  0.662  1.0
  Mg  Mg17  1  0.897  0.613  0.162  1.0
  Si  Si18  1  0.978  0.953  0.948  1.0
  Si  Si19  1  0.982  0.852  0.685  1.0
  Si  Si20  1  0.235  0.340  0.465  1.0
  Si  Si21  1  0.965  0.025  0.151  1.0
  Si  Si22  1  0.316  0.572  0.819  1.0
  Si  Si23  1  0.570  0.410  0.354  1.0
  Si  Si24  1  0.644  0.302  0.989  1.0
  Si  Si25  1  0.318  0.702  0.155  1.0
  Si  Si26  1  0.581  0.884  0.512  1.0
  Si  Si27  1  0.650  0.196  0.664  1.0
[/CIF]
.
The structure described by Mg9Si5 crystallizes in the triclinic P1 space group. There are eighteen inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(3), one Si(4), one Si(6), and one Si(8) atom. In the second Mg site, Mg(2) is bonded in a 3-coordinate geometry to one Si(2), one Si(6), and one Si(9) atom. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to one Si(4), one Si(6), one Si(8), and one Si(9) atom. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), and one Si(9) atom. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Si(3), one Si(8), and one Si(9) atom. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to one Si(10), one Si(3), one Si(6), and one Si(9) atom. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. In the eighth Mg site, Mg(8) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the ninth Mg site, Mg(9) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. In the tenth Mg site, Mg(10) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the eleventh Mg site, Mg(11) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. In the twelfth Mg site, Mg(12) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the thirteenth Mg site, Mg(13) is bonded in a 4-coordinate geometry to one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the fourteenth Mg site, Mg(14) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the sixteenth Mg site, Mg(16) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the seventeenth Mg site, Mg(17) is bonded to one Si(10), one Si(2), one Si(3), and one Si(5) atom to form distorted corner-sharing MgSi4 tetrahedra. In the eighteenth Mg site, Mg(18) is bonded in a distorted trigonal non-coplanar geometry to one Si(4), one Si(7), and one Si(8) atom. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(7), one Mg(8), one Mg(9), and one Si(4) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(4), one Mg(7), and one Mg(9) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(17), one Mg(4), one Mg(5), one Mg(6), and one Si(6) atom. In the fourth Si site, Si(4) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(3), and one Si(1) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(13), one Mg(15), one Mg(17), one Mg(7), one Mg(8), and one Mg(9) atom. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(2), one Mg(3), one Mg(6), and one Si(3) atom. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(7), one Mg(8), and one Mg(9) atom. In the eighth Si site, Si(8) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(10), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(3), one Mg(5), and one Mg(8) atom. In the ninth Si site, Si(9) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(15), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and one Si(10) atom. In the tenth Si site, Si(10) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(15), one Mg(17), one Mg(4), one Mg(6), one Mg(7), one Mg(9), and one Si(9) atom. is represented by the CIF file [CIF]
data_Mg9Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.255
_cell_length_b   7.267
_cell_length_c   12.397
_cell_angle_alpha   101.986
_cell_angle_beta   84.784
_cell_angle_gamma   118.865
_symmetry_Int_Tables_number   1
_cell_volume   559.870
_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  0.215  0.014  0.296  1.0
  Mg  Mg1  1  0.890  0.772  0.465  1.0
  Mg  Mg2  1  0.659  0.820  0.293  1.0
  Mg  Mg3  1  0.317  0.057  0.534  1.0
  Mg  Mg4  1  0.210  0.629  0.366  1.0
  Mg  Mg5  1  0.815  0.282  0.453  1.0
  Mg  Mg6  1  0.684  0.970  0.819  1.0
  Mg  Mg7  1  0.297  0.889  0.988  1.0
  Mg  Mg8  1  0.336  0.186  0.818  1.0
  Mg  Mg9  1  0.591  0.660  0.993  1.0
  Mg  Mg10  1  0.909  0.561  0.823  1.0
  Mg  Mg11  1  0.059  0.363  0.986  1.0
  Mg  Mg12  1  0.248  0.695  0.639  1.0
  Mg  Mg13  1  0.653  0.134  0.172  1.0
  Mg  Mg14  1  0.573  0.537  0.633  1.0
  Mg  Mg15  1  0.369  0.351  0.155  1.0
  Mg  Mg16  1  0.037  0.231  0.662  1.0
  Mg  Mg17  1  0.897  0.613  0.162  1.0
  Si  Si18  1  0.978  0.953  0.948  1.0
  Si  Si19  1  0.982  0.852  0.685  1.0
  Si  Si20  1  0.235  0.340  0.465  1.0
  Si  Si21  1  0.965  0.025  0.151  1.0
  Si  Si22  1  0.316  0.572  0.819  1.0
  Si  Si23  1  0.570  0.410  0.354  1.0
  Si  Si24  1  0.644  0.302  0.989  1.0
  Si  Si25  1  0.318  0.702  0.155  1.0
  Si  Si26  1  0.581  0.884  0.512  1.0
  Si  Si27  1  0.650  0.196  0.664  1.0
[/CIF]
.