The crystal structure described by Mg5Si6 crystallizes in the monoclinic Pm space group. There are ten inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted T-shaped geometry to one Si(1), one Si(2), and one Si(6) atom. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(12), one Si(3), one Si(8), and two equivalent Si(4) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(4), one Si(5), two equivalent Si(12), and two equivalent Si(8) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(10), one Si(4), one Si(6), two equivalent Si(11), two equivalent Si(3), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a 7-coordinate geometry to one Si(11), one Si(7), two equivalent Si(10), two equivalent Si(2), and two equivalent Si(6) atoms. In the sixth Mg site, Mg(6) is bonded in a 5-coordinate geometry to one Si(12), one Si(8), two equivalent Si(1), and two equivalent Si(5) atoms. In the seventh Mg site, Mg(7) is bonded in a 4-coordinate geometry to one Si(12), one Si(3), and two equivalent Si(4) atoms. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(4), two equivalent Si(11), two equivalent Si(3), and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a 8-coordinate geometry to two equivalent Si(1), two equivalent Si(10), two equivalent Si(2), and two equivalent Si(6) atoms. In the tenth Mg site, Mg(10) is bonded in a 8-coordinate geometry to two equivalent Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(9) atoms. There are twelve inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(10), two equivalent Mg(6), two equivalent Mg(9), one Si(2), and one Si(9) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(10), two equivalent Mg(5), two equivalent Mg(9), one Si(1), and one Si(10) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(7), two equivalent Mg(4), two equivalent Mg(8), one Si(11), and two equivalent Si(4) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(3), one Mg(4), one Mg(8), two equivalent Mg(2), two equivalent Mg(7), and two equivalent Si(3) atoms. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(3), two equivalent Mg(10), two equivalent Mg(6), one Si(9), and two equivalent Si(12) atoms. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(4), two equivalent Mg(5), two equivalent Mg(9), one Si(10), and two equivalent Si(11) atoms. In the seventh Si site, Si(7) is bonded in a 8-coordinate geometry to one Mg(5), two equivalent Mg(4), two equivalent Mg(8), one Si(11), and two equivalent Si(10) atoms. In the eighth Si site, Si(8) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(6), two equivalent Mg(3), one Si(12), and two equivalent Si(9) atoms. In the ninth Si site, Si(9) is bonded in a 6-coordinate geometry to two equivalent Mg(10), one Si(1), one Si(5), and two equivalent Si(8) atoms. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(4), two equivalent Mg(5), two equivalent Mg(9), one Si(2), one Si(6), and two equivalent Si(7) atoms. In the eleventh Si site, Si(11) is bonded in a 9-coordinate geometry to one Mg(5), two equivalent Mg(4), two equivalent Mg(8), one Si(3), one Si(7), and two equivalent Si(6) atoms. In the twelfth Si site, Si(12) is bonded in a 8-coordinate geometry to one Mg(2), one Mg(6), one Mg(7), two equivalent Mg(3), one Si(8), and two equivalent Si(5) atoms. is represented by the CIF file [CIF]
data_Mg5Si6
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.847
_cell_length_b   6.927
_cell_length_c   15.792
_cell_angle_alpha   81.997
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   416.731
_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  0.000  0.022  0.006  1.0
  Mg  Mg1  1  0.500  0.594  0.571  1.0
  Mg  Mg2  1  0.000  0.959  0.678  1.0
  Mg  Mg3  1  0.000  0.104  0.329  1.0
  Mg  Mg4  1  0.500  0.156  0.155  1.0
  Mg  Mg5  1  0.500  0.918  0.857  1.0
  Mg  Mg6  1  0.500  0.204  0.516  1.0
  Mg  Mg7  1  0.000  0.530  0.417  1.0
  Mg  Mg8  1  0.500  0.680  0.079  1.0
  Mg  Mg9  1  0.500  0.352  0.929  1.0
  Si  Si10  1  0.000  0.667  0.951  1.0
  Si  Si11  1  0.000  0.382  0.057  1.0
  Si  Si12  1  0.500  0.854  0.422  1.0
  Si  Si13  1  0.000  0.900  0.510  1.0
  Si  Si14  1  0.000  0.210  0.806  1.0
  Si  Si15  1  0.000  0.844  0.189  1.0
  Si  Si16  1  0.500  0.402  0.297  1.0
  Si  Si17  1  0.500  0.657  0.729  1.0
  Si  Si18  1  0.000  0.569  0.813  1.0
  Si  Si19  1  0.000  0.467  0.200  1.0
  Si  Si20  1  0.500  0.762  0.283  1.0
  Si  Si21  1  0.500  0.265  0.704  1.0
[/CIF]
.
The crystal structure described by Mg5Si6 crystallizes in the monoclinic Pm space group. There are ten inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted T-shaped geometry to one Si(1), one Si(2), and one Si(6) atom. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(12), one Si(3), one Si(8), and two equivalent Si(4) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(4), one Si(5), two equivalent Si(12), and two equivalent Si(8) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(10), one Si(4), one Si(6), two equivalent Si(11), two equivalent Si(3), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a 7-coordinate geometry to one Si(11), one Si(7), two equivalent Si(10), two equivalent Si(2), and two equivalent Si(6) atoms. In the sixth Mg site, Mg(6) is bonded in a 5-coordinate geometry to one Si(12), one Si(8), two equivalent Si(1), and two equivalent Si(5) atoms. In the seventh Mg site, Mg(7) is bonded in a 4-coordinate geometry to one Si(12), one Si(3), and two equivalent Si(4) atoms. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(4), two equivalent Si(11), two equivalent Si(3), and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a 8-coordinate geometry to two equivalent Si(1), two equivalent Si(10), two equivalent Si(2), and two equivalent Si(6) atoms. In the tenth Mg site, Mg(10) is bonded in a 8-coordinate geometry to two equivalent Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(9) atoms. There are twelve inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(10), two equivalent Mg(6), two equivalent Mg(9), one Si(2), and one Si(9) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(10), two equivalent Mg(5), two equivalent Mg(9), one Si(1), and one Si(10) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(7), two equivalent Mg(4), two equivalent Mg(8), one Si(11), and two equivalent Si(4) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(3), one Mg(4), one Mg(8), two equivalent Mg(2), two equivalent Mg(7), and two equivalent Si(3) atoms. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(3), two equivalent Mg(10), two equivalent Mg(6), one Si(9), and two equivalent Si(12) atoms. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(4), two equivalent Mg(5), two equivalent Mg(9), one Si(10), and two equivalent Si(11) atoms. In the seventh Si site, Si(7) is bonded in a 8-coordinate geometry to one Mg(5), two equivalent Mg(4), two equivalent Mg(8), one Si(11), and two equivalent Si(10) atoms. In the eighth Si site, Si(8) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(6), two equivalent Mg(3), one Si(12), and two equivalent Si(9) atoms. In the ninth Si site, Si(9) is bonded in a 6-coordinate geometry to two equivalent Mg(10), one Si(1), one Si(5), and two equivalent Si(8) atoms. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(4), two equivalent Mg(5), two equivalent Mg(9), one Si(2), one Si(6), and two equivalent Si(7) atoms. In the eleventh Si site, Si(11) is bonded in a 9-coordinate geometry to one Mg(5), two equivalent Mg(4), two equivalent Mg(8), one Si(3), one Si(7), and two equivalent Si(6) atoms. In the twelfth Si site, Si(12) is bonded in a 8-coordinate geometry to one Mg(2), one Mg(6), one Mg(7), two equivalent Mg(3), one Si(8), and two equivalent Si(5) atoms. is represented by the CIF file [CIF]
data_Mg5Si6
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.847
_cell_length_b   6.927
_cell_length_c   15.792
_cell_angle_alpha   81.997
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   416.731
_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  0.000  0.022  0.006  1.0
  Mg  Mg1  1  0.500  0.594  0.571  1.0
  Mg  Mg2  1  0.000  0.959  0.678  1.0
  Mg  Mg3  1  0.000  0.104  0.329  1.0
  Mg  Mg4  1  0.500  0.156  0.155  1.0
  Mg  Mg5  1  0.500  0.918  0.857  1.0
  Mg  Mg6  1  0.500  0.204  0.516  1.0
  Mg  Mg7  1  0.000  0.530  0.417  1.0
  Mg  Mg8  1  0.500  0.680  0.079  1.0
  Mg  Mg9  1  0.500  0.352  0.929  1.0
  Si  Si10  1  0.000  0.667  0.951  1.0
  Si  Si11  1  0.000  0.382  0.057  1.0
  Si  Si12  1  0.500  0.854  0.422  1.0
  Si  Si13  1  0.000  0.900  0.510  1.0
  Si  Si14  1  0.000  0.210  0.806  1.0
  Si  Si15  1  0.000  0.844  0.189  1.0
  Si  Si16  1  0.500  0.402  0.297  1.0
  Si  Si17  1  0.500  0.657  0.729  1.0
  Si  Si18  1  0.000  0.569  0.813  1.0
  Si  Si19  1  0.000  0.467  0.200  1.0
  Si  Si20  1  0.500  0.762  0.283  1.0
  Si  Si21  1  0.500  0.265  0.704  1.0
[/CIF]
.