The material described by K2Ca4Si8O21 crystallizes in the triclinic P-1 space group. K(1) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(2), one O(6), two equivalent O(11), and two equivalent O(9) atoms. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(10), one O(3), one O(4), one O(5), one O(8), and one O(9) atom. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(10), one O(4), one O(7), two equivalent O(3), and two equivalent O(5) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(11), one O(3), one O(6), and one O(8) atom to form corner-sharing SiO4 tetrahedra. In the third Si site, Si(3) is bonded to one O(1), one O(11), one O(2), and one O(9) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(10), one O(2), one O(7), and one O(8) atom to form corner-sharing SiO4 tetrahedra. There are eleven inequivalent O sites. In the first O site, O(11) is bonded in a 2-coordinate geometry to two equivalent K(1), one Si(2), and one Si(3) atom. In the second O site, O(1) is bonded in a linear geometry to two equivalent K(1) and two equivalent Si(3) atoms. In the third O site, O(2) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(3), and one Si(4) atom. In the fourth O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Ca(2), and one Si(2) atom. In the fifth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ca(2), and one Si(1) atom. In the sixth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the seventh O site, O(6) is bonded in a 2-coordinate geometry to one K(1), one Si(1), and one Si(2) atom. In the eighth O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(2), one Si(1), and one Si(4) atom. In the ninth O site, O(8) is bonded in a 3-coordinate geometry to one Ca(1), one Si(2), and one Si(4) atom. In the tenth O site, O(9) is bonded in a 4-coordinate geometry to two equivalent K(1), one Ca(1), and one Si(3) atom. In the eleventh O site, O(10) is bonded in a 4-coordinate geometry to one K(1), one Ca(1), one Ca(2), and one Si(4) atom. is represented by the CIF file [CIF]
data_K2Ca4Si8O21
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.883
_cell_length_b   7.194
_cell_length_c   11.333
_cell_angle_alpha   96.692
_cell_angle_beta   105.319
_cell_angle_gamma   109.127
_symmetry_Int_Tables_number   1
_cell_volume   498.487
_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
  K  K0  1  0.740  0.708  0.430  1.0
  K  K1  1  0.260  0.292  0.570  1.0
  Ca  Ca2  1  0.662  0.785  0.817  1.0
  Ca  Ca3  1  0.338  0.215  0.183  1.0
  Ca  Ca4  1  0.371  0.733  0.043  1.0
  Ca  Ca5  1  0.629  0.267  0.957  1.0
  Si  Si6  1  0.098  0.239  0.887  1.0
  Si  Si7  1  0.902  0.761  0.113  1.0
  Si  Si8  1  0.176  0.901  0.745  1.0
  Si  Si9  1  0.824  0.099  0.255  1.0
  Si  Si10  1  0.663  0.200  0.471  1.0
  Si  Si11  1  0.337  0.800  0.529  1.0
  Si  Si12  1  0.872  0.470  0.743  1.0
  Si  Si13  1  0.128  0.530  0.257  1.0
  O  O14  1  0.500  0.000  0.500  1.0
  O  O15  1  0.846  0.344  0.605  1.0
  O  O16  1  0.154  0.656  0.395  1.0
  O  O17  1  0.389  0.912  0.851  1.0
  O  O18  1  0.611  0.088  0.149  1.0
  O  O19  1  0.874  0.124  0.912  1.0
  O  O20  1  0.126  0.876  0.088  1.0
  O  O21  1  0.674  0.693  0.003  1.0
  O  O22  1  0.326  0.307  0.997  1.0
  O  O23  1  0.117  0.105  0.762  1.0
  O  O24  1  0.883  0.895  0.238  1.0
  O  O25  1  0.087  0.455  0.845  1.0
  O  O26  1  0.913  0.545  0.155  1.0
  O  O27  1  0.952  0.715  0.740  1.0
  O  O28  1  0.048  0.285  0.260  1.0
  O  O29  1  0.468  0.687  0.609  1.0
  O  O30  1  0.532  0.313  0.391  1.0
  O  O31  1  0.342  0.585  0.217  1.0
  O  O32  1  0.658  0.415  0.783  1.0
  O  O33  1  0.187  0.881  0.600  1.0
  O  O34  1  0.813  0.119  0.400  1.0
[/CIF]
.
The material described by K2Ca4Si8O21 crystallizes in the triclinic P-1 space group. K(1) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(2), one O(6), two equivalent O(11), and two equivalent O(9) atoms. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(10), one O(3), one O(4), one O(5), one O(8), and one O(9) atom. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(10), one O(4), one O(7), two equivalent O(3), and two equivalent O(5) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(11), one O(3), one O(6), and one O(8) atom to form corner-sharing SiO4 tetrahedra. In the third Si site, Si(3) is bonded to one O(1), one O(11), one O(2), and one O(9) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4) is bonded to one O(10), one O(2), one O(7), and one O(8) atom to form corner-sharing SiO4 tetrahedra. There are eleven inequivalent O sites. In the first O site, O(11) is bonded in a 2-coordinate geometry to two equivalent K(1), one Si(2), and one Si(3) atom. In the second O site, O(1) is bonded in a linear geometry to two equivalent K(1) and two equivalent Si(3) atoms. In the third O site, O(2) is bonded in a distorted bent 150 degrees geometry to one K(1), one Si(3), and one Si(4) atom. In the fourth O site, O(3) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Ca(2), and one Si(2) atom. In the fifth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1), one Ca(2), and one Si(1) atom. In the sixth O site, O(5) is bonded in a 3-coordinate geometry to one Ca(1), two equivalent Ca(2), and one Si(1) atom. In the seventh O site, O(6) is bonded in a 2-coordinate geometry to one K(1), one Si(1), and one Si(2) atom. In the eighth O site, O(7) is bonded in a distorted trigonal planar geometry to one Ca(2), one Si(1), and one Si(4) atom. In the ninth O site, O(8) is bonded in a 3-coordinate geometry to one Ca(1), one Si(2), and one Si(4) atom. In the tenth O site, O(9) is bonded in a 4-coordinate geometry to two equivalent K(1), one Ca(1), and one Si(3) atom. In the eleventh O site, O(10) is bonded in a 4-coordinate geometry to one K(1), one Ca(1), one Ca(2), and one Si(4) atom. is represented by the CIF file [CIF]
data_K2Ca4Si8O21
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.883
_cell_length_b   7.194
_cell_length_c   11.333
_cell_angle_alpha   96.692
_cell_angle_beta   105.319
_cell_angle_gamma   109.127
_symmetry_Int_Tables_number   1
_cell_volume   498.487
_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
  K  K0  1  0.740  0.708  0.430  1.0
  K  K1  1  0.260  0.292  0.570  1.0
  Ca  Ca2  1  0.662  0.785  0.817  1.0
  Ca  Ca3  1  0.338  0.215  0.183  1.0
  Ca  Ca4  1  0.371  0.733  0.043  1.0
  Ca  Ca5  1  0.629  0.267  0.957  1.0
  Si  Si6  1  0.098  0.239  0.887  1.0
  Si  Si7  1  0.902  0.761  0.113  1.0
  Si  Si8  1  0.176  0.901  0.745  1.0
  Si  Si9  1  0.824  0.099  0.255  1.0
  Si  Si10  1  0.663  0.200  0.471  1.0
  Si  Si11  1  0.337  0.800  0.529  1.0
  Si  Si12  1  0.872  0.470  0.743  1.0
  Si  Si13  1  0.128  0.530  0.257  1.0
  O  O14  1  0.500  0.000  0.500  1.0
  O  O15  1  0.846  0.344  0.605  1.0
  O  O16  1  0.154  0.656  0.395  1.0
  O  O17  1  0.389  0.912  0.851  1.0
  O  O18  1  0.611  0.088  0.149  1.0
  O  O19  1  0.874  0.124  0.912  1.0
  O  O20  1  0.126  0.876  0.088  1.0
  O  O21  1  0.674  0.693  0.003  1.0
  O  O22  1  0.326  0.307  0.997  1.0
  O  O23  1  0.117  0.105  0.762  1.0
  O  O24  1  0.883  0.895  0.238  1.0
  O  O25  1  0.087  0.455  0.845  1.0
  O  O26  1  0.913  0.545  0.155  1.0
  O  O27  1  0.952  0.715  0.740  1.0
  O  O28  1  0.048  0.285  0.260  1.0
  O  O29  1  0.468  0.687  0.609  1.0
  O  O30  1  0.532  0.313  0.391  1.0
  O  O31  1  0.342  0.585  0.217  1.0
  O  O32  1  0.658  0.415  0.783  1.0
  O  O33  1  0.187  0.881  0.600  1.0
  O  O34  1  0.813  0.119  0.400  1.0
[/CIF]
.