The crystal 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 5-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(6), and one Si(9) atom. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(6), and one Si(9) atom. In the fourth Mg site, Mg(4) is bonded in a 3-coordinate geometry to one Si(2), one Si(3), and one Si(9) atom. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(6), and one Si(9) atom. In the sixth Mg site, Mg(6) is bonded to one Si(10), one Si(2), one Si(3), and one Si(9) atom to form distorted corner-sharing MgSi4 tetrahedra. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(5), one Si(7), and one Si(8) atom. In the eighth Mg site, Mg(8) is bonded in a distorted see-saw-like geometry to one Si(1), one Si(4), one Si(7), and one Si(8) atom. In the ninth Mg site, Mg(9) is bonded in a distorted single-bond geometry to one Si(5), one Si(7), and one Si(8) atom. In the tenth Mg site, Mg(10) is bonded in a 3-coordinate geometry to one Si(1), one Si(4), one Si(5), one Si(7), and one Si(8) atom. In the eleventh Mg site, Mg(11) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(7), and one Si(8) atom. In the twelfth Mg site, Mg(12) is bonded in a 3-coordinate geometry to one Si(1), one Si(4), one Si(5), one Si(7), and one Si(8) atom. In the thirteenth Mg site, Mg(13) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(2), and one Si(3) atom. In the fourteenth Mg site, Mg(14) is bonded to one Si(4), one Si(6), one Si(7), one Si(8), and one Si(9) atom to form distorted corner-sharing MgSi5 tetrahedra. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(3), and one Si(5) atom. In the sixteenth Mg site, Mg(16) is bonded in a 4-coordinate geometry to one Si(4), one Si(6), one Si(7), one Si(8), and one Si(9) atom. In the seventeenth Mg site, Mg(17) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), and one Si(5) atom. In the eighteenth Mg site, Mg(18) is bonded in a 4-coordinate geometry to one Si(4), one Si(6), one Si(7), and one Si(9) atom. There are ten 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(12), one Mg(13), one Mg(15), one Mg(7), one Mg(8), and one Si(5) atom. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(3), one Mg(4), one Mg(5), and one Mg(6) atom. In the fourth Si site, Si(4) 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 fifth Si site, Si(5) is bonded in a 10-coordinate geometry to one Mg(10), one Mg(12), one Mg(15), one Mg(17), one Mg(2), one Mg(7), one Mg(9), one Si(1), one Si(10), and one Si(8) atom. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(3), one Mg(5), 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(10), one Mg(11), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(7), one Mg(8), one Mg(9), and one Si(6) atom. In the eighth Si site, Si(8) 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(7), one Mg(8), one Mg(9), and one Si(5) atom. In the ninth Si site, Si(9) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(2), one Mg(3), one Mg(4), one Mg(5), and one Mg(6) atom. In the tenth Si site, Si(10) is bonded in a 5-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(17), one Mg(6), one Mg(7), and one Si(5) atom. is represented by the CIF file [CIF]
data_Mg9Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.245
_cell_length_b   7.316
_cell_length_c   12.351
_cell_angle_alpha   73.119
_cell_angle_beta   81.163
_cell_angle_gamma   61.473
_symmetry_Int_Tables_number   1
_cell_volume   550.256
_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  0.213  0.839  0.355  1.0
  Mg  Mg1  1  0.877  0.127  0.537  1.0
  Mg  Mg2  1  0.013  0.501  0.356  1.0
  Mg  Mg3  1  0.391  0.379  0.533  1.0
  Mg  Mg4  1  0.665  0.068  0.358  1.0
  Mg  Mg5  1  0.616  0.662  0.507  1.0
  Mg  Mg6  1  0.394  0.204  0.824  1.0
  Mg  Mg7  1  0.231  0.979  0.036  1.0
  Mg  Mg8  1  0.942  0.463  0.872  1.0
  Mg  Mg9  1  0.025  0.702  0.018  1.0
  Mg  Mg10  1  0.451  0.593  0.903  1.0
  Mg  Mg11  1  0.745  0.148  0.982  1.0
  Mg  Mg12  1  0.039  0.326  0.651  1.0
  Mg  Mg13  1  0.613  0.840  0.187  1.0
  Mg  Mg14  1  0.211  0.715  0.683  1.0
  Mg  Mg15  1  0.903  0.327  0.157  1.0
  Mg  Mg16  1  0.580  0.863  0.688  1.0
  Mg  Mg17  1  0.390  0.510  0.181  1.0
  Si  Si18  1  0.136  0.982  0.831  1.0
  Si  Si19  1  0.292  0.072  0.497  1.0
  Si  Si20  1  0.960  0.726  0.522  1.0
  Si  Si21  1  0.962  0.890  0.190  1.0
  Si  Si22  1  0.821  0.971  0.792  1.0
  Si  Si23  1  0.294  0.177  0.261  1.0
  Si  Si24  1  0.309  0.302  0.036  1.0
  Si  Si25  1  0.648  0.772  0.972  1.0
  Si  Si26  1  0.637  0.465  0.348  1.0
  Si  Si27  1  0.641  0.398  0.724  1.0
[/CIF]
.
The crystal 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 5-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(6), and one Si(9) atom. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(6), and one Si(9) atom. In the fourth Mg site, Mg(4) is bonded in a 3-coordinate geometry to one Si(2), one Si(3), and one Si(9) atom. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(6), and one Si(9) atom. In the sixth Mg site, Mg(6) is bonded to one Si(10), one Si(2), one Si(3), and one Si(9) atom to form distorted corner-sharing MgSi4 tetrahedra. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(5), one Si(7), and one Si(8) atom. In the eighth Mg site, Mg(8) is bonded in a distorted see-saw-like geometry to one Si(1), one Si(4), one Si(7), and one Si(8) atom. In the ninth Mg site, Mg(9) is bonded in a distorted single-bond geometry to one Si(5), one Si(7), and one Si(8) atom. In the tenth Mg site, Mg(10) is bonded in a 3-coordinate geometry to one Si(1), one Si(4), one Si(5), one Si(7), and one Si(8) atom. In the eleventh Mg site, Mg(11) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(7), and one Si(8) atom. In the twelfth Mg site, Mg(12) is bonded in a 3-coordinate geometry to one Si(1), one Si(4), one Si(5), one Si(7), and one Si(8) atom. In the thirteenth Mg site, Mg(13) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(2), and one Si(3) atom. In the fourteenth Mg site, Mg(14) is bonded to one Si(4), one Si(6), one Si(7), one Si(8), and one Si(9) atom to form distorted corner-sharing MgSi5 tetrahedra. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(3), and one Si(5) atom. In the sixteenth Mg site, Mg(16) is bonded in a 4-coordinate geometry to one Si(4), one Si(6), one Si(7), one Si(8), and one Si(9) atom. In the seventeenth Mg site, Mg(17) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), and one Si(5) atom. In the eighteenth Mg site, Mg(18) is bonded in a 4-coordinate geometry to one Si(4), one Si(6), one Si(7), and one Si(9) atom. There are ten 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(12), one Mg(13), one Mg(15), one Mg(7), one Mg(8), and one Si(5) atom. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(3), one Mg(4), one Mg(5), and one Mg(6) atom. In the fourth Si site, Si(4) 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 fifth Si site, Si(5) is bonded in a 10-coordinate geometry to one Mg(10), one Mg(12), one Mg(15), one Mg(17), one Mg(2), one Mg(7), one Mg(9), one Si(1), one Si(10), and one Si(8) atom. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(3), one Mg(5), 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(10), one Mg(11), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(7), one Mg(8), one Mg(9), and one Si(6) atom. In the eighth Si site, Si(8) 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(7), one Mg(8), one Mg(9), and one Si(5) atom. In the ninth Si site, Si(9) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(2), one Mg(3), one Mg(4), one Mg(5), and one Mg(6) atom. In the tenth Si site, Si(10) is bonded in a 5-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(17), one Mg(6), one Mg(7), and one Si(5) atom. is represented by the CIF file [CIF]
data_Mg9Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.245
_cell_length_b   7.316
_cell_length_c   12.351
_cell_angle_alpha   73.119
_cell_angle_beta   81.163
_cell_angle_gamma   61.473
_symmetry_Int_Tables_number   1
_cell_volume   550.256
_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  0.213  0.839  0.355  1.0
  Mg  Mg1  1  0.877  0.127  0.537  1.0
  Mg  Mg2  1  0.013  0.501  0.356  1.0
  Mg  Mg3  1  0.391  0.379  0.533  1.0
  Mg  Mg4  1  0.665  0.068  0.358  1.0
  Mg  Mg5  1  0.616  0.662  0.507  1.0
  Mg  Mg6  1  0.394  0.204  0.824  1.0
  Mg  Mg7  1  0.231  0.979  0.036  1.0
  Mg  Mg8  1  0.942  0.463  0.872  1.0
  Mg  Mg9  1  0.025  0.702  0.018  1.0
  Mg  Mg10  1  0.451  0.593  0.903  1.0
  Mg  Mg11  1  0.745  0.148  0.982  1.0
  Mg  Mg12  1  0.039  0.326  0.651  1.0
  Mg  Mg13  1  0.613  0.840  0.187  1.0
  Mg  Mg14  1  0.211  0.715  0.683  1.0
  Mg  Mg15  1  0.903  0.327  0.157  1.0
  Mg  Mg16  1  0.580  0.863  0.688  1.0
  Mg  Mg17  1  0.390  0.510  0.181  1.0
  Si  Si18  1  0.136  0.982  0.831  1.0
  Si  Si19  1  0.292  0.072  0.497  1.0
  Si  Si20  1  0.960  0.726  0.522  1.0
  Si  Si21  1  0.962  0.890  0.190  1.0
  Si  Si22  1  0.821  0.971  0.792  1.0
  Si  Si23  1  0.294  0.177  0.261  1.0
  Si  Si24  1  0.309  0.302  0.036  1.0
  Si  Si25  1  0.648  0.772  0.972  1.0
  Si  Si26  1  0.637  0.465  0.348  1.0
  Si  Si27  1  0.641  0.398  0.724  1.0
[/CIF]
.