The material structure described by Mg5Si9 crystallizes in the triclinic P1 space group. There are ten inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to one Si(10), one Si(11), one Si(14), one Si(15), one Si(17), one Si(2), and one Si(8) atom. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(10), one Si(13), one Si(17), one Si(18), one Si(3), and one Si(7) atom. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(10), one Si(14), one Si(17), one Si(18), and one Si(3) atom. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to one Si(13), one Si(17), one Si(18), one Si(3), one Si(5), and one Si(7) atom. In the fifth Mg site, Mg(5) is bonded in a 4-coordinate geometry to one Si(10), one Si(14), one Si(17), one Si(18), one Si(6), and one Si(8) atom. In the sixth Mg site, Mg(6) is bonded in a distorted square pyramidal geometry to one Si(10), one Si(13), one Si(17), one Si(18), and one Si(3) atom. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(12), one Si(13), one Si(16), one Si(5), one Si(7), and one Si(9) atom. In the eighth Mg site, Mg(8) is bonded in a 8-coordinate geometry to one Si(11), one Si(12), one Si(14), one Si(15), one Si(16), one Si(2), one Si(4), and one Si(8) atom. In the ninth Mg site, Mg(9) is bonded in a 4-coordinate geometry to one Si(12), one Si(13), one Si(15), one Si(3), one Si(5), one Si(7), and one Si(9) atom. In the tenth Mg site, Mg(10) is bonded in a 5-coordinate geometry to one Si(12), one Si(15), one Si(16), one Si(6), and one Si(8) atom. There are eighteen inequivalent Si sites. In the first Si site, Si(1) is bonded in a 4-coordinate geometry to one Si(12), one Si(13), one Si(16), and one Si(5) atom. In the second Si site, Si(2) is bonded in a distorted hexagonal planar geometry to one Mg(1), one Mg(8), one Si(11), one Si(14), one Si(15), and one Si(16) atom. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), one Mg(4), one Mg(6), one Mg(9), one Si(7), and one Si(9) atom. In the fourth Si site, Si(4) is bonded in a 5-coordinate geometry to one Mg(8), one Si(10), one Si(11), one Si(14), and one Si(17) atom. In the fifth Si site, Si(5) is bonded in a 6-coordinate geometry to one Mg(4), one Mg(7), one Mg(9), one Si(1), one Si(18), and one Si(7) atom. In the sixth Si site, Si(6) is bonded in a 6-coordinate geometry to one Mg(10), one Mg(5), one Si(10), one Si(11), one Si(15), and one Si(8) atom. In the seventh Si site, Si(7) is bonded in a 8-coordinate geometry to one Mg(2), one Mg(4), one Mg(7), one Mg(9), one Si(13), one Si(3), one Si(5), and one Si(9) atom. In the eighth Si site, Si(8) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(10), one Mg(5), one Mg(8), one Si(14), one Si(17), and one Si(6) atom. In the ninth Si site, Si(9) is bonded in a 6-coordinate geometry to one Mg(7), one Mg(9), one Si(12), one Si(16), one Si(3), and one Si(7) atom. In the tenth Si site, Si(10) is bonded in a distorted pentagonal bipyramidal geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(5), one Mg(6), one Si(4), and one Si(6) atom. In the eleventh Si site, Si(11) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(8), one Si(12), one Si(2), one Si(4), and one Si(6) atom. In the twelfth Si site, Si(12) is bonded in a 7-coordinate geometry to one Mg(10), one Mg(7), one Mg(8), one Mg(9), one Si(1), one Si(11), and one Si(9) atom. In the thirteenth Si site, Si(13) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(4), one Mg(6), one Mg(7), one Mg(9), one Si(1), and one Si(7) atom. In the fourteenth Si site, Si(14) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(3), one Mg(5), one Mg(8), one Si(2), one Si(4), and one Si(8) atom. In the fifteenth Si site, Si(15) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(10), one Mg(8), one Mg(9), one Si(2), and one Si(6) atom. In the sixteenth Si site, Si(16) is bonded in a 6-coordinate geometry to one Mg(10), one Mg(7), one Mg(8), one Si(1), one Si(2), and one Si(9) atom. In the seventeenth Si site, Si(17) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), one Si(4), and one Si(8) atom. In the eighteenth Si site, Si(18) is bonded in a 6-coordinate geometry to one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and one Si(5) atom. is represented by the CIF file [CIF]
data_Mg5Si9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.890
_cell_length_b   7.461
_cell_length_c   12.642
_cell_angle_alpha   83.827
_cell_angle_beta   77.663
_cell_angle_gamma   60.258
_symmetry_Int_Tables_number   1
_cell_volume   551.221
_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  0.484  0.052  0.722  1.0
  Mg  Mg1  1  0.225  0.904  0.435  1.0
  Mg  Mg2  1  0.490  0.409  0.535  1.0
  Mg  Mg3  1  0.782  0.565  0.375  1.0
  Mg  Mg4  1  0.035  0.340  0.567  1.0
  Mg  Mg5  1  0.736  0.939  0.470  1.0
  Mg  Mg6  1  0.418  0.763  0.170  1.0
  Mg  Mg7  1  0.841  0.812  0.890  1.0
  Mg  Mg8  1  0.606  0.233  0.129  1.0
  Mg  Mg9  1  0.492  0.594  0.942  1.0
  Si  Si10  1  0.901  0.739  0.143  1.0
  Si  Si11  1  0.151  0.344  0.897  1.0
  Si  Si12  1  0.852  0.192  0.330  1.0
  Si  Si13  1  0.186  0.807  0.708  1.0
  Si  Si14  1  0.210  0.530  0.239  1.0
  Si  Si15  1  0.762  0.272  0.783  1.0
  Si  Si16  1  0.211  0.205  0.271  1.0
  Si  Si17  1  0.744  0.605  0.744  1.0
  Si  Si18  1  0.020  0.187  0.140  1.0
  Si  Si19  1  0.878  0.074  0.622  1.0
  Si  Si20  1  0.100  0.057  0.852  1.0
  Si  Si21  1  0.095  0.911  0.031  1.0
  Si  Si22  1  0.583  0.937  0.284  1.0
  Si  Si23  1  0.143  0.497  0.723  1.0
  Si  Si24  1  0.519  0.213  0.931  1.0
  Si  Si25  1  0.847  0.511  0.047  1.0
  Si  Si26  1  0.546  0.722  0.594  1.0
  Si  Si27  1  0.143  0.586  0.427  1.0
[/CIF]
.
The material structure described by Mg5Si9 crystallizes in the triclinic P1 space group. There are ten inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to one Si(10), one Si(11), one Si(14), one Si(15), one Si(17), one Si(2), and one Si(8) atom. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(10), one Si(13), one Si(17), one Si(18), one Si(3), and one Si(7) atom. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(10), one Si(14), one Si(17), one Si(18), and one Si(3) atom. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to one Si(13), one Si(17), one Si(18), one Si(3), one Si(5), and one Si(7) atom. In the fifth Mg site, Mg(5) is bonded in a 4-coordinate geometry to one Si(10), one Si(14), one Si(17), one Si(18), one Si(6), and one Si(8) atom. In the sixth Mg site, Mg(6) is bonded in a distorted square pyramidal geometry to one Si(10), one Si(13), one Si(17), one Si(18), and one Si(3) atom. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(12), one Si(13), one Si(16), one Si(5), one Si(7), and one Si(9) atom. In the eighth Mg site, Mg(8) is bonded in a 8-coordinate geometry to one Si(11), one Si(12), one Si(14), one Si(15), one Si(16), one Si(2), one Si(4), and one Si(8) atom. In the ninth Mg site, Mg(9) is bonded in a 4-coordinate geometry to one Si(12), one Si(13), one Si(15), one Si(3), one Si(5), one Si(7), and one Si(9) atom. In the tenth Mg site, Mg(10) is bonded in a 5-coordinate geometry to one Si(12), one Si(15), one Si(16), one Si(6), and one Si(8) atom. There are eighteen inequivalent Si sites. In the first Si site, Si(1) is bonded in a 4-coordinate geometry to one Si(12), one Si(13), one Si(16), and one Si(5) atom. In the second Si site, Si(2) is bonded in a distorted hexagonal planar geometry to one Mg(1), one Mg(8), one Si(11), one Si(14), one Si(15), and one Si(16) atom. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), one Mg(4), one Mg(6), one Mg(9), one Si(7), and one Si(9) atom. In the fourth Si site, Si(4) is bonded in a 5-coordinate geometry to one Mg(8), one Si(10), one Si(11), one Si(14), and one Si(17) atom. In the fifth Si site, Si(5) is bonded in a 6-coordinate geometry to one Mg(4), one Mg(7), one Mg(9), one Si(1), one Si(18), and one Si(7) atom. In the sixth Si site, Si(6) is bonded in a 6-coordinate geometry to one Mg(10), one Mg(5), one Si(10), one Si(11), one Si(15), and one Si(8) atom. In the seventh Si site, Si(7) is bonded in a 8-coordinate geometry to one Mg(2), one Mg(4), one Mg(7), one Mg(9), one Si(13), one Si(3), one Si(5), and one Si(9) atom. In the eighth Si site, Si(8) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(10), one Mg(5), one Mg(8), one Si(14), one Si(17), and one Si(6) atom. In the ninth Si site, Si(9) is bonded in a 6-coordinate geometry to one Mg(7), one Mg(9), one Si(12), one Si(16), one Si(3), and one Si(7) atom. In the tenth Si site, Si(10) is bonded in a distorted pentagonal bipyramidal geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(5), one Mg(6), one Si(4), and one Si(6) atom. In the eleventh Si site, Si(11) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(8), one Si(12), one Si(2), one Si(4), and one Si(6) atom. In the twelfth Si site, Si(12) is bonded in a 7-coordinate geometry to one Mg(10), one Mg(7), one Mg(8), one Mg(9), one Si(1), one Si(11), and one Si(9) atom. In the thirteenth Si site, Si(13) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(4), one Mg(6), one Mg(7), one Mg(9), one Si(1), and one Si(7) atom. In the fourteenth Si site, Si(14) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(3), one Mg(5), one Mg(8), one Si(2), one Si(4), and one Si(8) atom. In the fifteenth Si site, Si(15) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(10), one Mg(8), one Mg(9), one Si(2), and one Si(6) atom. In the sixteenth Si site, Si(16) is bonded in a 6-coordinate geometry to one Mg(10), one Mg(7), one Mg(8), one Si(1), one Si(2), and one Si(9) atom. In the seventeenth Si site, Si(17) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), one Si(4), and one Si(8) atom. In the eighteenth Si site, Si(18) is bonded in a 6-coordinate geometry to one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and one Si(5) atom. is represented by the CIF file [CIF]
data_Mg5Si9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.890
_cell_length_b   7.461
_cell_length_c   12.642
_cell_angle_alpha   83.827
_cell_angle_beta   77.663
_cell_angle_gamma   60.258
_symmetry_Int_Tables_number   1
_cell_volume   551.221
_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  0.484  0.052  0.722  1.0
  Mg  Mg1  1  0.225  0.904  0.435  1.0
  Mg  Mg2  1  0.490  0.409  0.535  1.0
  Mg  Mg3  1  0.782  0.565  0.375  1.0
  Mg  Mg4  1  0.035  0.340  0.567  1.0
  Mg  Mg5  1  0.736  0.939  0.470  1.0
  Mg  Mg6  1  0.418  0.763  0.170  1.0
  Mg  Mg7  1  0.841  0.812  0.890  1.0
  Mg  Mg8  1  0.606  0.233  0.129  1.0
  Mg  Mg9  1  0.492  0.594  0.942  1.0
  Si  Si10  1  0.901  0.739  0.143  1.0
  Si  Si11  1  0.151  0.344  0.897  1.0
  Si  Si12  1  0.852  0.192  0.330  1.0
  Si  Si13  1  0.186  0.807  0.708  1.0
  Si  Si14  1  0.210  0.530  0.239  1.0
  Si  Si15  1  0.762  0.272  0.783  1.0
  Si  Si16  1  0.211  0.205  0.271  1.0
  Si  Si17  1  0.744  0.605  0.744  1.0
  Si  Si18  1  0.020  0.187  0.140  1.0
  Si  Si19  1  0.878  0.074  0.622  1.0
  Si  Si20  1  0.100  0.057  0.852  1.0
  Si  Si21  1  0.095  0.911  0.031  1.0
  Si  Si22  1  0.583  0.937  0.284  1.0
  Si  Si23  1  0.143  0.497  0.723  1.0
  Si  Si24  1  0.519  0.213  0.931  1.0
  Si  Si25  1  0.847  0.511  0.047  1.0
  Si  Si26  1  0.546  0.722  0.594  1.0
  Si  Si27  1  0.143  0.586  0.427  1.0
[/CIF]
.