The structure described by Mg5Si6 crystallizes in the monoclinic Cm space group. There are ten inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), one Si(6), and two equivalent Si(5) atoms. In the second Mg site, Mg(2) is bonded in a rectangular see-saw-like geometry to one Si(3), one Si(4), one Si(7), and one Si(8) atom. In the third Mg site, Mg(3) is bonded in a 8-coordinate geometry to two equivalent Si(12), two equivalent Si(4), two equivalent Si(8), and two equivalent Si(9) atoms. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to one Si(10), 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 8-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 7-coordinate geometry to one Si(5), two equivalent Si(1), two equivalent Si(12), and two equivalent Si(8) atoms. In the seventh Mg site, Mg(7) is bonded in a 6-coordinate geometry to two equivalent Si(3), two equivalent Si(4), and two equivalent Si(8) atoms. In the eighth Mg site, Mg(8) is bonded in a 8-coordinate geometry to two equivalent Si(11), two equivalent Si(3), two equivalent Si(4), and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a 9-coordinate geometry to one Si(5), 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 5-coordinate geometry to one Si(5), two equivalent Si(1), and two equivalent Si(2) atoms. There are twelve inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to one Mg(1), two equivalent Mg(10), two equivalent Mg(6), two equivalent Mg(9), one Si(2), and two equivalent Si(5) atoms. 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), two equivalent Mg(4), two equivalent Mg(7), two equivalent Mg(8), one Si(11), and one Si(4) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(2), two equivalent Mg(3), two equivalent Mg(7), two equivalent Mg(8), one Si(12), and one Si(3) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(6), one Mg(9), two equivalent Mg(1), two equivalent Si(1), and two equivalent Si(9) 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 9-coordinate geometry to one Mg(2), 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 8-coordinate geometry to one Mg(2), two equivalent Mg(3), two equivalent Mg(6), two equivalent Mg(7), and one Si(9) atom. In the ninth Si site, Si(9) is bonded in a 6-coordinate geometry to two equivalent Mg(3), one Si(12), one Si(8), and two equivalent Si(5) 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 6-coordinate geometry to two equivalent Mg(3), two equivalent Mg(6), one Si(4), and one Si(9) atom. is represented by the CIF file [CIF]
data_Mg5Si6
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   15.026
_cell_length_b   15.026
_cell_length_c   6.953
_cell_angle_alpha   76.661
_cell_angle_beta   76.661
_cell_angle_gamma   15.257
_symmetry_Int_Tables_number   1
_cell_volume   401.735
_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  0.701  0.701  0.230  1.0
  Mg  Mg1  1  0.440  0.440  0.363  1.0
  Mg  Mg2  1  0.020  0.020  0.451  1.0
  Mg  Mg3  1  0.866  0.866  0.253  1.0
  Mg  Mg4  1  0.274  0.274  0.348  1.0
  Mg  Mg5  1  0.083  0.083  0.941  1.0
  Mg  Mg6  1  0.981  0.981  0.998  1.0
  Mg  Mg7  1  0.905  0.905  0.713  1.0
  Mg  Mg8  1  0.230  0.230  0.877  1.0
  Mg  Mg9  1  0.154  0.154  0.574  1.0
  Si  Si10  1  0.656  0.656  0.895  1.0
  Si  Si11  1  0.719  0.719  0.595  1.0
  Si  Si12  1  0.415  0.415  0.008  1.0
  Si  Si13  1  0.474  0.474  0.699  1.0
  Si  Si14  1  0.140  0.140  0.192  1.0
  Si  Si15  1  0.790  0.790  0.018  1.0
  Si  Si16  1  0.346  0.346  0.573  1.0
  Si  Si17  1  0.529  0.529  0.147  1.0
  Si  Si18  1  0.589  0.589  0.328  1.0
  Si  Si19  1  0.796  0.796  0.650  1.0
  Si  Si20  1  0.340  0.340  0.944  1.0
  Si  Si21  1  0.557  0.557  0.699  1.0
[/CIF]
.
The structure described by Mg5Si6 crystallizes in the monoclinic Cm space group. There are ten inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), one Si(6), and two equivalent Si(5) atoms. In the second Mg site, Mg(2) is bonded in a rectangular see-saw-like geometry to one Si(3), one Si(4), one Si(7), and one Si(8) atom. In the third Mg site, Mg(3) is bonded in a 8-coordinate geometry to two equivalent Si(12), two equivalent Si(4), two equivalent Si(8), and two equivalent Si(9) atoms. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to one Si(10), 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 8-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 7-coordinate geometry to one Si(5), two equivalent Si(1), two equivalent Si(12), and two equivalent Si(8) atoms. In the seventh Mg site, Mg(7) is bonded in a 6-coordinate geometry to two equivalent Si(3), two equivalent Si(4), and two equivalent Si(8) atoms. In the eighth Mg site, Mg(8) is bonded in a 8-coordinate geometry to two equivalent Si(11), two equivalent Si(3), two equivalent Si(4), and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a 9-coordinate geometry to one Si(5), 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 5-coordinate geometry to one Si(5), two equivalent Si(1), and two equivalent Si(2) atoms. There are twelve inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to one Mg(1), two equivalent Mg(10), two equivalent Mg(6), two equivalent Mg(9), one Si(2), and two equivalent Si(5) atoms. 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), two equivalent Mg(4), two equivalent Mg(7), two equivalent Mg(8), one Si(11), and one Si(4) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(2), two equivalent Mg(3), two equivalent Mg(7), two equivalent Mg(8), one Si(12), and one Si(3) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(6), one Mg(9), two equivalent Mg(1), two equivalent Si(1), and two equivalent Si(9) 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 9-coordinate geometry to one Mg(2), 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 8-coordinate geometry to one Mg(2), two equivalent Mg(3), two equivalent Mg(6), two equivalent Mg(7), and one Si(9) atom. In the ninth Si site, Si(9) is bonded in a 6-coordinate geometry to two equivalent Mg(3), one Si(12), one Si(8), and two equivalent Si(5) 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 6-coordinate geometry to two equivalent Mg(3), two equivalent Mg(6), one Si(4), and one Si(9) atom. is represented by the CIF file [CIF]
data_Mg5Si6
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   15.026
_cell_length_b   15.026
_cell_length_c   6.953
_cell_angle_alpha   76.661
_cell_angle_beta   76.661
_cell_angle_gamma   15.257
_symmetry_Int_Tables_number   1
_cell_volume   401.735
_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  0.701  0.701  0.230  1.0
  Mg  Mg1  1  0.440  0.440  0.363  1.0
  Mg  Mg2  1  0.020  0.020  0.451  1.0
  Mg  Mg3  1  0.866  0.866  0.253  1.0
  Mg  Mg4  1  0.274  0.274  0.348  1.0
  Mg  Mg5  1  0.083  0.083  0.941  1.0
  Mg  Mg6  1  0.981  0.981  0.998  1.0
  Mg  Mg7  1  0.905  0.905  0.713  1.0
  Mg  Mg8  1  0.230  0.230  0.877  1.0
  Mg  Mg9  1  0.154  0.154  0.574  1.0
  Si  Si10  1  0.656  0.656  0.895  1.0
  Si  Si11  1  0.719  0.719  0.595  1.0
  Si  Si12  1  0.415  0.415  0.008  1.0
  Si  Si13  1  0.474  0.474  0.699  1.0
  Si  Si14  1  0.140  0.140  0.192  1.0
  Si  Si15  1  0.790  0.790  0.018  1.0
  Si  Si16  1  0.346  0.346  0.573  1.0
  Si  Si17  1  0.529  0.529  0.147  1.0
  Si  Si18  1  0.589  0.589  0.328  1.0
  Si  Si19  1  0.796  0.796  0.650  1.0
  Si  Si20  1  0.340  0.340  0.944  1.0
  Si  Si21  1  0.557  0.557  0.699  1.0
[/CIF]
.