The structure described by Na8Si7O18 crystallizes in the triclinic P1 space group. There are eight inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to one O(1), one O(12), one O(2), and one O(6) atom. In the second Na site, Na(2) is bonded in a trigonal non-coplanar geometry to one O(4), one O(7), and one O(9) atom. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(1), one O(17), one O(2), one O(4), and one O(5) atom. In the fourth Na site, Na(4) is bonded in a distorted rectangular see-saw-like geometry to one O(10), one O(12), one O(3), and one O(6) atom. In the fifth Na site, Na(5) is bonded in a 4-coordinate geometry to one O(10), one O(12), one O(15), and one O(7) atom. In the sixth Na site, Na(6) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(4), and one O(5) atom. In the seventh Na site, Na(7) is bonded in a distorted T-shaped geometry to one O(3), one O(6), and one O(9) atom. In the eighth Na site, Na(8) is bonded in a 6-coordinate geometry to one O(10), one O(12), one O(13), one O(16), one O(18), and one O(9) atom. There are seven inequivalent Si sites. In the first Si site, Si(1) is bonded in a bent 120 degrees geometry to one O(11) and one O(8) atom. In the second Si site, Si(2) is bonded in a tetrahedral geometry to one O(11), one O(17), one O(18), and one O(4) atom. In the third Si site, Si(3) is bonded to one O(10), one O(13), one O(14), and one O(2) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4) is bonded in a bent 120 degrees geometry to one O(15) and one O(6) atom. In the fifth Si site, Si(5) is bonded to one O(1), one O(14), one O(15), and one O(8) atom to form corner-sharing SiO4 tetrahedra. In the sixth Si site, Si(6) is bonded in a tetrahedral geometry to one O(16), one O(5), one O(7), and one O(9) atom. In the seventh Si site, Si(7) is bonded in a water-like geometry to one O(18) and one O(3) atom. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal pyramidal geometry to one Na(1), one Na(3), one Na(6), and one Si(5) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(3), one Na(6), and one Si(3) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Na(4), one Na(7), and one Si(7) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), one Na(3), one Na(6), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Na(3), one Na(6), and one Si(6) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Na(1), one Na(4), one Na(7), and one Si(4) atom. In the seventh O site, O(7) is bonded in a trigonal non-coplanar geometry to one Na(2), one Na(5), and one Si(6) atom. In the eighth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Si(1) and one Si(5) atom. In the ninth O site, O(9) is bonded in a distorted tetrahedral geometry to one Na(2), one Na(7), one Na(8), and one Si(6) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Na(4), one Na(5), one Na(8), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Na(1), one Na(4), one Na(5), one Na(8), and one O(13) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one Na(8), one Si(3), and one O(12) atom. In the fourteenth O site, O(14) is bonded in a bent 120 degrees geometry to one Si(3) and one Si(5) atom. In the fifteenth O site, O(15) is bonded in a trigonal planar geometry to one Na(5), one Si(4), and one Si(5) atom. In the sixteenth O site, O(16) is bonded in a 2-coordinate geometry to one Na(8) and one Si(6) atom. In the seventeenth O site, O(17) is bonded in a distorted single-bond geometry to one Na(3) and one Si(2) atom. In the eighteenth O site, O(18) is bonded in a 3-coordinate geometry to one Na(8), one Si(2), and one Si(7) atom. is represented by the CIF file [CIF]
data_Na8Si7O18
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.278
_cell_length_b   9.069
_cell_length_c   10.971
_cell_angle_alpha   103.327
_cell_angle_beta   101.116
_cell_angle_gamma   104.509
_symmetry_Int_Tables_number   1
_cell_volume   567.209
_cell_formula_units_Z   1
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
  Na  Na0  1  0.272  0.704  0.263  1.0
  Na  Na1  1  0.583  0.311  0.724  1.0
  Na  Na2  1  0.466  0.549  0.966  1.0
  Na  Na3  1  0.947  0.873  0.463  1.0
  Na  Na4  1  0.404  0.485  0.480  1.0
  Na  Na5  1  0.960  0.435  0.991  1.0
  Na  Na6  1  0.578  0.110  0.485  1.0
  Na  Na7  1  0.920  0.567  0.549  1.0
  Si  Si8  1  0.972  0.020  0.011  1.0
  Si  Si9  1  0.941  0.691  0.856  1.0
  Si  Si10  1  0.790  0.540  0.265  1.0
  Si  Si11  1  0.120  0.089  0.258  1.0
  Si  Si12  1  0.349  0.334  0.154  1.0
  Si  Si13  1  0.096  0.365  0.686  1.0
  Si  Si14  1  0.785  0.932  0.752  1.0
  O  O15  1  0.287  0.485  0.130  1.0
  O  O16  1  0.879  0.636  0.170  1.0
  O  O17  1  0.707  0.963  0.618  1.0
  O  O18  1  0.755  0.544  0.864  1.0
  O  O19  1  0.125  0.331  0.825  1.0
  O  O20  1  0.204  0.995  0.352  1.0
  O  O21  1  0.260  0.313  0.598  1.0
  O  O22  1  0.200  0.167  0.032  1.0
  O  O23  1  0.836  0.335  0.602  1.0
  O  O24  1  0.689  0.623  0.379  1.0
  O  O25  1  0.021  0.848  0.986  1.0
  O  O26  1  0.171  0.630  0.433  1.0
  O  O27  1  0.005  0.479  0.344  1.0
  O  O28  1  0.620  0.352  0.175  1.0
  O  O29  1  0.289  0.270  0.282  1.0
  O  O30  1  0.217  0.581  0.724  1.0
  O  O31  1  0.203  0.679  0.852  1.0
  O  O32  1  0.849  0.763  0.732  1.0
[/CIF]
.
The structure described by Na8Si7O18 crystallizes in the triclinic P1 space group. There are eight inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to one O(1), one O(12), one O(2), and one O(6) atom. In the second Na site, Na(2) is bonded in a trigonal non-coplanar geometry to one O(4), one O(7), and one O(9) atom. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(1), one O(17), one O(2), one O(4), and one O(5) atom. In the fourth Na site, Na(4) is bonded in a distorted rectangular see-saw-like geometry to one O(10), one O(12), one O(3), and one O(6) atom. In the fifth Na site, Na(5) is bonded in a 4-coordinate geometry to one O(10), one O(12), one O(15), and one O(7) atom. In the sixth Na site, Na(6) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(4), and one O(5) atom. In the seventh Na site, Na(7) is bonded in a distorted T-shaped geometry to one O(3), one O(6), and one O(9) atom. In the eighth Na site, Na(8) is bonded in a 6-coordinate geometry to one O(10), one O(12), one O(13), one O(16), one O(18), and one O(9) atom. There are seven inequivalent Si sites. In the first Si site, Si(1) is bonded in a bent 120 degrees geometry to one O(11) and one O(8) atom. In the second Si site, Si(2) is bonded in a tetrahedral geometry to one O(11), one O(17), one O(18), and one O(4) atom. In the third Si site, Si(3) is bonded to one O(10), one O(13), one O(14), and one O(2) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4) is bonded in a bent 120 degrees geometry to one O(15) and one O(6) atom. In the fifth Si site, Si(5) is bonded to one O(1), one O(14), one O(15), and one O(8) atom to form corner-sharing SiO4 tetrahedra. In the sixth Si site, Si(6) is bonded in a tetrahedral geometry to one O(16), one O(5), one O(7), and one O(9) atom. In the seventh Si site, Si(7) is bonded in a water-like geometry to one O(18) and one O(3) atom. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal pyramidal geometry to one Na(1), one Na(3), one Na(6), and one Si(5) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(3), one Na(6), and one Si(3) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Na(4), one Na(7), and one Si(7) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), one Na(3), one Na(6), and one Si(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Na(3), one Na(6), and one Si(6) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Na(1), one Na(4), one Na(7), and one Si(4) atom. In the seventh O site, O(7) is bonded in a trigonal non-coplanar geometry to one Na(2), one Na(5), and one Si(6) atom. In the eighth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Si(1) and one Si(5) atom. In the ninth O site, O(9) is bonded in a distorted tetrahedral geometry to one Na(2), one Na(7), one Na(8), and one Si(6) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Na(4), one Na(5), one Na(8), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Na(1), one Na(4), one Na(5), one Na(8), and one O(13) atom. In the thirteenth O site, O(13) is bonded in a distorted single-bond geometry to one Na(8), one Si(3), and one O(12) atom. In the fourteenth O site, O(14) is bonded in a bent 120 degrees geometry to one Si(3) and one Si(5) atom. In the fifteenth O site, O(15) is bonded in a trigonal planar geometry to one Na(5), one Si(4), and one Si(5) atom. In the sixteenth O site, O(16) is bonded in a 2-coordinate geometry to one Na(8) and one Si(6) atom. In the seventeenth O site, O(17) is bonded in a distorted single-bond geometry to one Na(3) and one Si(2) atom. In the eighteenth O site, O(18) is bonded in a 3-coordinate geometry to one Na(8), one Si(2), and one Si(7) atom. is represented by the CIF file [CIF]
data_Na8Si7O18
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.278
_cell_length_b   9.069
_cell_length_c   10.971
_cell_angle_alpha   103.327
_cell_angle_beta   101.116
_cell_angle_gamma   104.509
_symmetry_Int_Tables_number   1
_cell_volume   567.209
_cell_formula_units_Z   1
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
  Na  Na0  1  0.272  0.704  0.263  1.0
  Na  Na1  1  0.583  0.311  0.724  1.0
  Na  Na2  1  0.466  0.549  0.966  1.0
  Na  Na3  1  0.947  0.873  0.463  1.0
  Na  Na4  1  0.404  0.485  0.480  1.0
  Na  Na5  1  0.960  0.435  0.991  1.0
  Na  Na6  1  0.578  0.110  0.485  1.0
  Na  Na7  1  0.920  0.567  0.549  1.0
  Si  Si8  1  0.972  0.020  0.011  1.0
  Si  Si9  1  0.941  0.691  0.856  1.0
  Si  Si10  1  0.790  0.540  0.265  1.0
  Si  Si11  1  0.120  0.089  0.258  1.0
  Si  Si12  1  0.349  0.334  0.154  1.0
  Si  Si13  1  0.096  0.365  0.686  1.0
  Si  Si14  1  0.785  0.932  0.752  1.0
  O  O15  1  0.287  0.485  0.130  1.0
  O  O16  1  0.879  0.636  0.170  1.0
  O  O17  1  0.707  0.963  0.618  1.0
  O  O18  1  0.755  0.544  0.864  1.0
  O  O19  1  0.125  0.331  0.825  1.0
  O  O20  1  0.204  0.995  0.352  1.0
  O  O21  1  0.260  0.313  0.598  1.0
  O  O22  1  0.200  0.167  0.032  1.0
  O  O23  1  0.836  0.335  0.602  1.0
  O  O24  1  0.689  0.623  0.379  1.0
  O  O25  1  0.021  0.848  0.986  1.0
  O  O26  1  0.171  0.630  0.433  1.0
  O  O27  1  0.005  0.479  0.344  1.0
  O  O28  1  0.620  0.352  0.175  1.0
  O  O29  1  0.289  0.270  0.282  1.0
  O  O30  1  0.217  0.581  0.724  1.0
  O  O31  1  0.203  0.679  0.852  1.0
  O  O32  1  0.849  0.763  0.732  1.0
[/CIF]
.