The material 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 2-coordinate geometry to one Mg(3), one Si(10), one Si(14), and one Si(8) atom. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Mg(3), one Si(10), one Si(13), one Si(18), and one Si(7) atom. In the third Mg site, Mg(3) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(2), one Mg(4), one Mg(5), one Si(10), one Si(14), and one Si(17) atom. In the fourth Mg site, Mg(4) is bonded in a 3-coordinate geometry to one Mg(3), one Si(10), one Si(13), and one Si(18) atom. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Mg(3), one Si(18), one Si(4), and one Si(6) atom. In the sixth Mg site, Mg(6) is bonded in a 2-coordinate geometry to one Si(17), one Si(18), one Si(3), and one Si(9) atom. In the seventh Mg site, Mg(7) is bonded in a 4-coordinate geometry to one Si(1), one Si(15), one Si(3), and one Si(5) atom. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(15), one Si(16), one Si(2), and one Si(6) atom. In the ninth Mg site, Mg(9) is bonded in a 5-coordinate geometry to one Si(1), one Si(11), one Si(13), one Si(16), and one Si(7) atom. In the tenth Mg site, Mg(10) is bonded in a 2-coordinate geometry to one Si(14), one Si(17), one Si(2), and one Si(4) atom. There are eighteen inequivalent Si sites. In the first Si site, Si(1) is bonded in a 4-coordinate geometry to one Mg(7), one Mg(9), one Si(12), and one Si(7) atom. In the second Si site, Si(2) is bonded in a 4-coordinate geometry to one Mg(10), one Mg(8), one Si(11), and one Si(14) atom. In the third Si site, Si(3) is bonded in a distorted single-bond geometry to one Mg(6), one Mg(7), one Si(18), one Si(5), and one Si(9) atom. In the fourth Si site, Si(4) is bonded in a 5-coordinate geometry to one Mg(10), one Mg(5), one Si(10), one Si(14), and one Si(17) atom. In the fifth Si site, Si(5) is bonded in a 5-coordinate geometry to one Mg(7), one Si(12), one Si(18), one Si(3), and one Si(9) atom. In the sixth Si site, Si(6) is bonded in a distorted single-bond geometry to one Mg(5), one Mg(8), and one Si(14) atom. In the seventh Si site, Si(7) is bonded in a 4-coordinate geometry to one Mg(2), one Mg(9), one Si(1), and one Si(9) atom. In the eighth Si site, Si(8) is bonded in a distorted single-bond geometry to one Mg(1) and one Si(14) atom. In the ninth Si site, Si(9) is bonded in a 4-coordinate geometry to one Mg(6), one Si(3), one Si(5), and one Si(7) atom. In the tenth Si site, Si(10) is bonded in a 2-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), and one Si(4) atom. In the eleventh Si site, Si(11) is bonded in a 1-coordinate geometry to one Mg(9) and one Si(2) atom. In the twelfth Si site, Si(12) is bonded in a 2-coordinate geometry to one Si(1), one Si(16), and one Si(5) atom. In the thirteenth Si site, Si(13) is bonded in a 3-coordinate geometry to one Mg(2), one Mg(4), and one Mg(9) atom. In the fourteenth Si site, Si(14) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(10), one Mg(3), one Si(2), one Si(4), one Si(6), and one Si(8) atom. In the fifteenth Si site, Si(15) is bonded in a 2-coordinate geometry to one Mg(7) and one Mg(8) atom. In the sixteenth Si site, Si(16) is bonded in a 3-coordinate geometry to one Mg(8), one Mg(9), and one Si(12) atom. In the seventeenth Si site, Si(17) is bonded in a 2-coordinate geometry to one Mg(10), one Mg(3), one Mg(6), and one Si(4) atom. In the eighteenth Si site, Si(18) is bonded in a 6-coordinate geometry to one Mg(2), one Mg(4), one Mg(5), one Mg(6), one Si(3), 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   6.053
_cell_length_b   6.861
_cell_length_c   13.568
_cell_angle_alpha   104.505
_cell_angle_beta   93.154
_cell_angle_gamma   106.827
_symmetry_Int_Tables_number   1
_cell_volume   517.228
_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  0.410  0.782  0.690  1.0
  Mg  Mg1  1  0.763  0.404  0.406  1.0
  Mg  Mg2  1  0.622  0.632  0.538  1.0
  Mg  Mg3  1  0.239  0.332  0.401  1.0
  Mg  Mg4  1  0.961  0.034  0.606  1.0
  Mg  Mg5  1  0.204  0.864  0.452  1.0
  Mg  Mg6  1  0.541  0.536  0.124  1.0
  Mg  Mg7  1  0.173  0.354  0.926  1.0
  Mg  Mg8  1  0.494  0.017  0.086  1.0
  Mg  Mg9  1  0.402  0.257  0.759  1.0
  Si  Si10  1  0.150  0.182  0.134  1.0
  Si  Si11  1  0.597  0.569  0.886  1.0
  Si  Si12  1  0.444  0.754  0.330  1.0
  Si  Si13  1  0.843  0.333  0.686  1.0
  Si  Si14  1  0.803  0.863  0.255  1.0
  Si  Si15  1  0.948  0.068  0.822  1.0
  Si  Si16  1  0.848  0.268  0.212  1.0
  Si  Si17  1  0.177  0.827  0.829  1.0
  Si  Si18  1  0.032  0.630  0.244  1.0
  Si  Si19  1  0.137  0.484  0.575  1.0
  Si  Si20  1  0.642  0.908  0.924  1.0
  Si  Si21  1  0.970  0.864  0.076  1.0
  Si  Si22  1  0.450  0.136  0.283  1.0
  Si  Si23  1  0.815  0.635  0.744  1.0
  Si  Si24  1  0.835  0.386  0.021  1.0
  Si  Si25  1  0.175  0.687  0.011  1.0
  Si  Si26  1  0.505  0.177  0.574  1.0
  Si  Si27  1  0.821  0.016  0.404  1.0
[/CIF]
.
The material 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 2-coordinate geometry to one Mg(3), one Si(10), one Si(14), and one Si(8) atom. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Mg(3), one Si(10), one Si(13), one Si(18), and one Si(7) atom. In the third Mg site, Mg(3) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(2), one Mg(4), one Mg(5), one Si(10), one Si(14), and one Si(17) atom. In the fourth Mg site, Mg(4) is bonded in a 3-coordinate geometry to one Mg(3), one Si(10), one Si(13), and one Si(18) atom. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Mg(3), one Si(18), one Si(4), and one Si(6) atom. In the sixth Mg site, Mg(6) is bonded in a 2-coordinate geometry to one Si(17), one Si(18), one Si(3), and one Si(9) atom. In the seventh Mg site, Mg(7) is bonded in a 4-coordinate geometry to one Si(1), one Si(15), one Si(3), and one Si(5) atom. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(15), one Si(16), one Si(2), and one Si(6) atom. In the ninth Mg site, Mg(9) is bonded in a 5-coordinate geometry to one Si(1), one Si(11), one Si(13), one Si(16), and one Si(7) atom. In the tenth Mg site, Mg(10) is bonded in a 2-coordinate geometry to one Si(14), one Si(17), one Si(2), and one Si(4) atom. There are eighteen inequivalent Si sites. In the first Si site, Si(1) is bonded in a 4-coordinate geometry to one Mg(7), one Mg(9), one Si(12), and one Si(7) atom. In the second Si site, Si(2) is bonded in a 4-coordinate geometry to one Mg(10), one Mg(8), one Si(11), and one Si(14) atom. In the third Si site, Si(3) is bonded in a distorted single-bond geometry to one Mg(6), one Mg(7), one Si(18), one Si(5), and one Si(9) atom. In the fourth Si site, Si(4) is bonded in a 5-coordinate geometry to one Mg(10), one Mg(5), one Si(10), one Si(14), and one Si(17) atom. In the fifth Si site, Si(5) is bonded in a 5-coordinate geometry to one Mg(7), one Si(12), one Si(18), one Si(3), and one Si(9) atom. In the sixth Si site, Si(6) is bonded in a distorted single-bond geometry to one Mg(5), one Mg(8), and one Si(14) atom. In the seventh Si site, Si(7) is bonded in a 4-coordinate geometry to one Mg(2), one Mg(9), one Si(1), and one Si(9) atom. In the eighth Si site, Si(8) is bonded in a distorted single-bond geometry to one Mg(1) and one Si(14) atom. In the ninth Si site, Si(9) is bonded in a 4-coordinate geometry to one Mg(6), one Si(3), one Si(5), and one Si(7) atom. In the tenth Si site, Si(10) is bonded in a 2-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), and one Si(4) atom. In the eleventh Si site, Si(11) is bonded in a 1-coordinate geometry to one Mg(9) and one Si(2) atom. In the twelfth Si site, Si(12) is bonded in a 2-coordinate geometry to one Si(1), one Si(16), and one Si(5) atom. In the thirteenth Si site, Si(13) is bonded in a 3-coordinate geometry to one Mg(2), one Mg(4), and one Mg(9) atom. In the fourteenth Si site, Si(14) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(10), one Mg(3), one Si(2), one Si(4), one Si(6), and one Si(8) atom. In the fifteenth Si site, Si(15) is bonded in a 2-coordinate geometry to one Mg(7) and one Mg(8) atom. In the sixteenth Si site, Si(16) is bonded in a 3-coordinate geometry to one Mg(8), one Mg(9), and one Si(12) atom. In the seventeenth Si site, Si(17) is bonded in a 2-coordinate geometry to one Mg(10), one Mg(3), one Mg(6), and one Si(4) atom. In the eighteenth Si site, Si(18) is bonded in a 6-coordinate geometry to one Mg(2), one Mg(4), one Mg(5), one Mg(6), one Si(3), 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   6.053
_cell_length_b   6.861
_cell_length_c   13.568
_cell_angle_alpha   104.505
_cell_angle_beta   93.154
_cell_angle_gamma   106.827
_symmetry_Int_Tables_number   1
_cell_volume   517.228
_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  0.410  0.782  0.690  1.0
  Mg  Mg1  1  0.763  0.404  0.406  1.0
  Mg  Mg2  1  0.622  0.632  0.538  1.0
  Mg  Mg3  1  0.239  0.332  0.401  1.0
  Mg  Mg4  1  0.961  0.034  0.606  1.0
  Mg  Mg5  1  0.204  0.864  0.452  1.0
  Mg  Mg6  1  0.541  0.536  0.124  1.0
  Mg  Mg7  1  0.173  0.354  0.926  1.0
  Mg  Mg8  1  0.494  0.017  0.086  1.0
  Mg  Mg9  1  0.402  0.257  0.759  1.0
  Si  Si10  1  0.150  0.182  0.134  1.0
  Si  Si11  1  0.597  0.569  0.886  1.0
  Si  Si12  1  0.444  0.754  0.330  1.0
  Si  Si13  1  0.843  0.333  0.686  1.0
  Si  Si14  1  0.803  0.863  0.255  1.0
  Si  Si15  1  0.948  0.068  0.822  1.0
  Si  Si16  1  0.848  0.268  0.212  1.0
  Si  Si17  1  0.177  0.827  0.829  1.0
  Si  Si18  1  0.032  0.630  0.244  1.0
  Si  Si19  1  0.137  0.484  0.575  1.0
  Si  Si20  1  0.642  0.908  0.924  1.0
  Si  Si21  1  0.970  0.864  0.076  1.0
  Si  Si22  1  0.450  0.136  0.283  1.0
  Si  Si23  1  0.815  0.635  0.744  1.0
  Si  Si24  1  0.835  0.386  0.021  1.0
  Si  Si25  1  0.175  0.687  0.011  1.0
  Si  Si26  1  0.505  0.177  0.574  1.0
  Si  Si27  1  0.821  0.016  0.404  1.0
[/CIF]
.