The compound described by Mg9Si5 crystallizes in the triclinic P1 space group. There are eighteen inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(10), one Si(3), one Si(6), and one Si(9) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the third Mg site, Mg(3) is bonded to one Si(10), one Si(3), one Si(6), and one Si(9) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(5), and one Si(9) atom. In the fifth Mg site, Mg(5) is bonded to one Si(10), one Si(3), one Si(6), and one Si(9) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the sixth Mg site, Mg(6) is bonded to one Si(10), one Si(2), one Si(5), and one Si(9) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the seventh Mg site, Mg(7) is bonded in a distorted single-bond geometry to one Si(5) and one Si(7) atom. In the eighth Mg site, Mg(8) is bonded in a distorted trigonal non-coplanar geometry to one Si(4), one Si(6), and one Si(8) atom. In the ninth Mg site, Mg(9) is bonded in a distorted trigonal non-coplanar geometry to one Si(1), one Si(7), and one Si(8) atom. In the tenth Mg site, Mg(10) is bonded in a distorted trigonal non-coplanar geometry to one Si(4), one Si(6), and one Si(8) atom. In the eleventh Mg site, Mg(11) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), and one Si(7) atom. In the twelfth Mg site, Mg(12) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form distorted corner-sharing MgSi4 trigonal pyramids. In the thirteenth Mg site, Mg(13) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(2), and one Si(5) atom. In the fourteenth Mg site, Mg(14) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), one Si(8), and one Si(9) atom. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(2), and one Si(5) atom. In the sixteenth Mg site, Mg(16) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), one Si(8), and one Si(9) atom. In the seventeenth Mg site, Mg(17) is bonded in a distorted trigonal non-coplanar geometry to one Si(1), one Si(7), and one Si(8) atom. In the eighteenth Mg site, Mg(18) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), one Si(8), and one Si(9) atom. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(9), one Si(2), and one Si(5) atom. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(2), one Mg(4), one Mg(6), and one Si(1) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(2), one Mg(3), one Mg(5), and one Si(4) atom. In the fourth Si site, Si(4) is bonded in a 6-coordinate geometry to one Mg(10), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(8), and one Si(3) atom. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(15), one Mg(2), one Mg(4), one Mg(6), one Mg(7), one Si(1), and one Si(7) atom. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(10), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(3), one Mg(5), and one Mg(8) atom. In the seventh Si site, Si(7) is bonded in a 6-coordinate geometry to one Mg(11), one Mg(12), one Mg(17), one Mg(7), one Mg(9), and one Si(5) atom. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to one Mg(10), one Mg(12), one Mg(14), one Mg(16), one Mg(17), one Mg(18), one Mg(8), and one Mg(9) atom. In the ninth Si site, Si(9) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(2), one Mg(3), one Mg(4), one Mg(5), and one Mg(6) atom. In the tenth Si site, Si(10) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(2), one Mg(3), one Mg(4), one Mg(5), and one Mg(6) atom. is represented by the CIF card [CIF]
data_Mg9Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.183
_cell_length_b   7.194
_cell_length_c   13.195
_cell_angle_alpha   87.630
_cell_angle_beta   103.113
_cell_angle_gamma   119.516
_symmetry_Int_Tables_number   1
_cell_volume   575.948
_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  0.922  0.343  0.376  1.0
  Mg  Mg1  1  0.133  0.777  0.517  1.0
  Mg  Mg2  1  0.407  0.115  0.376  1.0
  Mg  Mg3  1  0.717  0.978  0.534  1.0
  Mg  Mg4  1  0.674  0.623  0.369  1.0
  Mg  Mg5  1  0.401  0.455  0.543  1.0
  Mg  Mg6  1  0.895  0.102  0.866  1.0
  Mg  Mg7  1  0.778  0.295  0.057  1.0
  Mg  Mg8  1  0.451  0.876  0.936  1.0
  Mg  Mg9  1  0.208  0.030  0.052  1.0
  Mg  Mg10  1  0.363  0.237  0.852  1.0
  Mg  Mg11  1  0.518  0.560  0.054  1.0
  Mg  Mg12  1  0.087  0.419  0.694  1.0
  Mg  Mg13  1  0.004  0.701  0.218  1.0
  Mg  Mg14  1  0.585  0.200  0.690  1.0
  Mg  Mg15  1  0.535  0.915  0.216  1.0
  Mg  Mg16  1  0.939  0.579  0.863  1.0
  Mg  Mg17  1  0.216  0.369  0.217  1.0
  Si  Si18  1  0.216  0.843  0.739  1.0
  Si  Si19  1  0.139  0.089  0.637  1.0
  Si  Si20  1  0.979  0.017  0.332  1.0
  Si  Si21  1  0.865  0.974  0.129  1.0
  Si  Si22  1  0.495  0.780  0.694  1.0
  Si  Si23  1  0.584  0.326  0.210  1.0
  Si  Si24  1  0.620  0.670  0.857  1.0
  Si  Si25  1  0.178  0.632  0.062  1.0
  Si  Si26  1  0.337  0.696  0.380  1.0
  Si  Si27  1  0.753  0.398  0.529  1.0
[/CIF]
.
The compound described by Mg9Si5 crystallizes in the triclinic P1 space group. There are eighteen inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(10), one Si(3), one Si(6), and one Si(9) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the third Mg site, Mg(3) is bonded to one Si(10), one Si(3), one Si(6), and one Si(9) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(5), and one Si(9) atom. In the fifth Mg site, Mg(5) is bonded to one Si(10), one Si(3), one Si(6), and one Si(9) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the sixth Mg site, Mg(6) is bonded to one Si(10), one Si(2), one Si(5), and one Si(9) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the seventh Mg site, Mg(7) is bonded in a distorted single-bond geometry to one Si(5) and one Si(7) atom. In the eighth Mg site, Mg(8) is bonded in a distorted trigonal non-coplanar geometry to one Si(4), one Si(6), and one Si(8) atom. In the ninth Mg site, Mg(9) is bonded in a distorted trigonal non-coplanar geometry to one Si(1), one Si(7), and one Si(8) atom. In the tenth Mg site, Mg(10) is bonded in a distorted trigonal non-coplanar geometry to one Si(4), one Si(6), and one Si(8) atom. In the eleventh Mg site, Mg(11) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), and one Si(7) atom. In the twelfth Mg site, Mg(12) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form distorted corner-sharing MgSi4 trigonal pyramids. In the thirteenth Mg site, Mg(13) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(2), and one Si(5) atom. In the fourteenth Mg site, Mg(14) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), one Si(8), and one Si(9) atom. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(2), and one Si(5) atom. In the sixteenth Mg site, Mg(16) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), one Si(8), and one Si(9) atom. In the seventeenth Mg site, Mg(17) is bonded in a distorted trigonal non-coplanar geometry to one Si(1), one Si(7), and one Si(8) atom. In the eighteenth Mg site, Mg(18) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), one Si(8), and one Si(9) atom. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(9), one Si(2), and one Si(5) atom. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(2), one Mg(4), one Mg(6), and one Si(1) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(2), one Mg(3), one Mg(5), and one Si(4) atom. In the fourth Si site, Si(4) is bonded in a 6-coordinate geometry to one Mg(10), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(8), and one Si(3) atom. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(15), one Mg(2), one Mg(4), one Mg(6), one Mg(7), one Si(1), and one Si(7) atom. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(10), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(3), one Mg(5), and one Mg(8) atom. In the seventh Si site, Si(7) is bonded in a 6-coordinate geometry to one Mg(11), one Mg(12), one Mg(17), one Mg(7), one Mg(9), and one Si(5) atom. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to one Mg(10), one Mg(12), one Mg(14), one Mg(16), one Mg(17), one Mg(18), one Mg(8), and one Mg(9) atom. In the ninth Si site, Si(9) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(2), one Mg(3), one Mg(4), one Mg(5), and one Mg(6) atom. In the tenth Si site, Si(10) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(2), one Mg(3), one Mg(4), one Mg(5), and one Mg(6) atom. is represented by the CIF card [CIF]
data_Mg9Si5
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.183
_cell_length_b   7.194
_cell_length_c   13.195
_cell_angle_alpha   87.630
_cell_angle_beta   103.113
_cell_angle_gamma   119.516
_symmetry_Int_Tables_number   1
_cell_volume   575.948
_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  0.922  0.343  0.376  1.0
  Mg  Mg1  1  0.133  0.777  0.517  1.0
  Mg  Mg2  1  0.407  0.115  0.376  1.0
  Mg  Mg3  1  0.717  0.978  0.534  1.0
  Mg  Mg4  1  0.674  0.623  0.369  1.0
  Mg  Mg5  1  0.401  0.455  0.543  1.0
  Mg  Mg6  1  0.895  0.102  0.866  1.0
  Mg  Mg7  1  0.778  0.295  0.057  1.0
  Mg  Mg8  1  0.451  0.876  0.936  1.0
  Mg  Mg9  1  0.208  0.030  0.052  1.0
  Mg  Mg10  1  0.363  0.237  0.852  1.0
  Mg  Mg11  1  0.518  0.560  0.054  1.0
  Mg  Mg12  1  0.087  0.419  0.694  1.0
  Mg  Mg13  1  0.004  0.701  0.218  1.0
  Mg  Mg14  1  0.585  0.200  0.690  1.0
  Mg  Mg15  1  0.535  0.915  0.216  1.0
  Mg  Mg16  1  0.939  0.579  0.863  1.0
  Mg  Mg17  1  0.216  0.369  0.217  1.0
  Si  Si18  1  0.216  0.843  0.739  1.0
  Si  Si19  1  0.139  0.089  0.637  1.0
  Si  Si20  1  0.979  0.017  0.332  1.0
  Si  Si21  1  0.865  0.974  0.129  1.0
  Si  Si22  1  0.495  0.780  0.694  1.0
  Si  Si23  1  0.584  0.326  0.210  1.0
  Si  Si24  1  0.620  0.670  0.857  1.0
  Si  Si25  1  0.178  0.632  0.062  1.0
  Si  Si26  1  0.337  0.696  0.380  1.0
  Si  Si27  1  0.753  0.398  0.529  1.0
[/CIF]
.