The material described by Mg6Si5 crystallizes in the monoclinic Pm space group. There are twelve inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(9), two equivalent Si(3), and two equivalent Si(4) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one Si(1), one Si(6), two equivalent Si(5), and two equivalent Si(8) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(3), one Si(7), two equivalent Si(10), and two equivalent Si(2) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(9), two equivalent Si(4), two equivalent Si(5), and two equivalent Si(8) atoms. In the fifth Mg site, Mg(5) is bonded to one Si(1), two equivalent Si(4), and two equivalent Si(5) atoms to form distorted MgSi5 trigonal bipyramids that share edges with two equivalent Mg(9)Si4 tetrahedra and edges with two equivalent Mg(5)Si5 trigonal bipyramids. In the sixth Mg site, Mg(6) is bonded in a 6-coordinate geometry to one Si(10), one Si(6), two equivalent Si(3), and two equivalent Si(7) atoms. In the seventh Mg site, Mg(7) is bonded in a 8-coordinate geometry to one Si(7), one Si(8), two equivalent Si(1), two equivalent Si(10), and two equivalent Si(2) atoms. In the eighth Mg site, Mg(8) is bonded in a 7-coordinate geometry to one Si(5), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(6) atoms. In the ninth Mg site, Mg(9) is bonded to one Si(4), one Si(5), and two equivalent Si(9) atoms to form distorted MgSi4 tetrahedra that share corners with two equivalent Mg(10)Si4 tetrahedra, corners with two equivalent Mg(9)Si4 tetrahedra, and edges with two equivalent Mg(5)Si5 trigonal bipyramids. In the tenth Mg site, Mg(10) is bonded to one Si(10), one Si(9), and two equivalent Si(3) atoms to form distorted corner-sharing MgSi4 tetrahedra. In the eleventh Mg site, Mg(11) is bonded in a 6-coordinate geometry to one Si(3), one Si(7), two equivalent Si(10), and two equivalent Si(9) atoms. In the twelfth Mg site, Mg(12) is bonded in a 4-coordinate geometry to one Si(3), one Si(4), and two equivalent Si(9) atoms. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(5), two equivalent Mg(7), two equivalent Mg(8), one Si(2), and two equivalent Si(8) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Mg(3), two equivalent Mg(7), two equivalent Mg(8), one Si(1), one Si(10), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(11), one Mg(12), one Mg(3), two equivalent Mg(1), two equivalent Mg(10), and two equivalent Mg(6) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(12), one Mg(9), two equivalent Mg(1), two equivalent Mg(4), two equivalent Mg(5), and one Si(8) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(8), one Mg(9), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), and one Si(8) atom. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(6), two equivalent Mg(8), one Si(2), and two equivalent Si(7) atoms. In the seventh Si site, Si(7) is bonded in a 7-coordinate geometry to one Mg(11), one Mg(3), one Mg(7), two equivalent Mg(6), and two equivalent Si(6) atoms. In the eighth Si site, Si(8) is bonded in a distorted q6 geometry to one Mg(7), two equivalent Mg(2), two equivalent Mg(4), one Si(4), one Si(5), and two equivalent Si(1) atoms. In the ninth Si site, Si(9) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(10), one Mg(4), two equivalent Mg(11), two equivalent Mg(12), and two equivalent Mg(9) atoms. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(6), two equivalent Mg(11), two equivalent Mg(3), two equivalent Mg(7), and one Si(2) atom. is represented by the CIF card [CIF]
data_Mg6Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.180
_cell_length_b   7.113
_cell_length_c   14.023
_cell_angle_alpha   83.134
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   413.922
_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  0.500  0.389  0.064  1.0
  Mg  Mg1  1  0.500  0.787  0.436  1.0
  Mg  Mg2  1  0.000  0.267  0.739  1.0
  Mg  Mg3  1  0.500  0.968  0.215  1.0
  Mg  Mg4  1  0.500  0.462  0.290  1.0
  Mg  Mg5  1  0.500  0.560  0.824  1.0
  Mg  Mg6  1  0.000  0.002  0.568  1.0
  Mg  Mg7  1  0.000  0.461  0.488  1.0
  Mg  Mg8  1  0.000  0.649  0.132  1.0
  Mg  Mg9  1  0.500  0.142  0.895  1.0
  Mg  Mg10  1  0.000  0.817  0.883  1.0
  Mg  Mg11  1  0.000  0.058  0.052  1.0
  Si  Si12  1  0.500  0.173  0.439  1.0
  Si  Si13  1  0.500  0.244  0.604  1.0
  Si  Si14  1  0.000  0.383  0.925  1.0
  Si  Si15  1  0.000  0.269  0.198  1.0
  Si  Si16  1  0.000  0.737  0.320  1.0
  Si  Si17  1  0.500  0.579  0.616  1.0
  Si  Si18  1  0.000  0.700  0.696  1.0
  Si  Si19  1  0.000  0.077  0.354  1.0
  Si  Si20  1  0.500  0.813  0.027  1.0
  Si  Si21  1  0.500  0.968  0.732  1.0
[/CIF]
.
The material described by Mg6Si5 crystallizes in the monoclinic Pm space group. There are twelve inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(9), two equivalent Si(3), and two equivalent Si(4) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to one Si(1), one Si(6), two equivalent Si(5), and two equivalent Si(8) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(3), one Si(7), two equivalent Si(10), and two equivalent Si(2) atoms. In the fourth Mg site, Mg(4) is bonded in a 7-coordinate geometry to one Si(9), two equivalent Si(4), two equivalent Si(5), and two equivalent Si(8) atoms. In the fifth Mg site, Mg(5) is bonded to one Si(1), two equivalent Si(4), and two equivalent Si(5) atoms to form distorted MgSi5 trigonal bipyramids that share edges with two equivalent Mg(9)Si4 tetrahedra and edges with two equivalent Mg(5)Si5 trigonal bipyramids. In the sixth Mg site, Mg(6) is bonded in a 6-coordinate geometry to one Si(10), one Si(6), two equivalent Si(3), and two equivalent Si(7) atoms. In the seventh Mg site, Mg(7) is bonded in a 8-coordinate geometry to one Si(7), one Si(8), two equivalent Si(1), two equivalent Si(10), and two equivalent Si(2) atoms. In the eighth Mg site, Mg(8) is bonded in a 7-coordinate geometry to one Si(5), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(6) atoms. In the ninth Mg site, Mg(9) is bonded to one Si(4), one Si(5), and two equivalent Si(9) atoms to form distorted MgSi4 tetrahedra that share corners with two equivalent Mg(10)Si4 tetrahedra, corners with two equivalent Mg(9)Si4 tetrahedra, and edges with two equivalent Mg(5)Si5 trigonal bipyramids. In the tenth Mg site, Mg(10) is bonded to one Si(10), one Si(9), and two equivalent Si(3) atoms to form distorted corner-sharing MgSi4 tetrahedra. In the eleventh Mg site, Mg(11) is bonded in a 6-coordinate geometry to one Si(3), one Si(7), two equivalent Si(10), and two equivalent Si(9) atoms. In the twelfth Mg site, Mg(12) is bonded in a 4-coordinate geometry to one Si(3), one Si(4), and two equivalent Si(9) atoms. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(5), two equivalent Mg(7), two equivalent Mg(8), one Si(2), and two equivalent Si(8) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Mg(3), two equivalent Mg(7), two equivalent Mg(8), one Si(1), one Si(10), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(11), one Mg(12), one Mg(3), two equivalent Mg(1), two equivalent Mg(10), and two equivalent Mg(6) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(12), one Mg(9), two equivalent Mg(1), two equivalent Mg(4), two equivalent Mg(5), and one Si(8) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(8), one Mg(9), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), and one Si(8) atom. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(6), two equivalent Mg(8), one Si(2), and two equivalent Si(7) atoms. In the seventh Si site, Si(7) is bonded in a 7-coordinate geometry to one Mg(11), one Mg(3), one Mg(7), two equivalent Mg(6), and two equivalent Si(6) atoms. In the eighth Si site, Si(8) is bonded in a distorted q6 geometry to one Mg(7), two equivalent Mg(2), two equivalent Mg(4), one Si(4), one Si(5), and two equivalent Si(1) atoms. In the ninth Si site, Si(9) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(10), one Mg(4), two equivalent Mg(11), two equivalent Mg(12), and two equivalent Mg(9) atoms. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(6), two equivalent Mg(11), two equivalent Mg(3), two equivalent Mg(7), and one Si(2) atom. is represented by the CIF card [CIF]
data_Mg6Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.180
_cell_length_b   7.113
_cell_length_c   14.023
_cell_angle_alpha   83.134
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   413.922
_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  0.500  0.389  0.064  1.0
  Mg  Mg1  1  0.500  0.787  0.436  1.0
  Mg  Mg2  1  0.000  0.267  0.739  1.0
  Mg  Mg3  1  0.500  0.968  0.215  1.0
  Mg  Mg4  1  0.500  0.462  0.290  1.0
  Mg  Mg5  1  0.500  0.560  0.824  1.0
  Mg  Mg6  1  0.000  0.002  0.568  1.0
  Mg  Mg7  1  0.000  0.461  0.488  1.0
  Mg  Mg8  1  0.000  0.649  0.132  1.0
  Mg  Mg9  1  0.500  0.142  0.895  1.0
  Mg  Mg10  1  0.000  0.817  0.883  1.0
  Mg  Mg11  1  0.000  0.058  0.052  1.0
  Si  Si12  1  0.500  0.173  0.439  1.0
  Si  Si13  1  0.500  0.244  0.604  1.0
  Si  Si14  1  0.000  0.383  0.925  1.0
  Si  Si15  1  0.000  0.269  0.198  1.0
  Si  Si16  1  0.000  0.737  0.320  1.0
  Si  Si17  1  0.500  0.579  0.616  1.0
  Si  Si18  1  0.000  0.700  0.696  1.0
  Si  Si19  1  0.000  0.077  0.354  1.0
  Si  Si20  1  0.500  0.813  0.027  1.0
  Si  Si21  1  0.500  0.968  0.732  1.0
[/CIF]
.