The material described by Na2SrSi2O6 crystallizes in the monoclinic C2/m space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to four equivalent O(4) and four equivalent O(5) atoms to form distorted NaO8 hexagonal bipyramids that share corners with eight equivalent Na(2)O8 hexagonal bipyramids, edges with four equivalent Sr(2)O8 hexagonal bipyramids, edges with two equivalent Si(2)O4 tetrahedra, and edges with four equivalent Si(1)O4 tetrahedra. In the second Na site, Na(2) is bonded to two equivalent O(3), two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms to form distorted NaO8 hexagonal bipyramids that share corners with four equivalent Na(1)O8 hexagonal bipyramids, corners with four equivalent Na(2)O8 hexagonal bipyramids, edges with two equivalent Na(3)O8 hexagonal bipyramids, edges with two equivalent Sr(2)O8 hexagonal bipyramids, edges with two equivalent Si(2)O4 tetrahedra, and edges with four equivalent Si(1)O4 tetrahedra. In the third Na site, Na(3) is bonded to two equivalent O(3), two equivalent O(6), and four equivalent O(1) atoms to form distorted NaO8 hexagonal bipyramids that share corners with four equivalent Sr(2)O8 hexagonal bipyramids, corners with two equivalent Si(2)O4 tetrahedra, edges with four equivalent Na(2)O8 hexagonal bipyramids, edges with two equivalent Sr(1)O6 octahedra, and edges with four equivalent Si(1)O4 tetrahedra. In the fourth Na site, Na(4) is bonded in a 6-coordinate geometry to one O(2), one O(6), two equivalent O(1), and two equivalent O(5) atoms. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form SrO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Na(3)O8 hexagonal bipyramids, and edges with four equivalent Sr(2)O8 hexagonal bipyramids. In the second Sr site, Sr(2) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form SrO8 hexagonal bipyramids that share corners with two equivalent Na(3)O8 hexagonal bipyramids, corners with two equivalent Sr(2)O8 hexagonal bipyramids, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Na(1)O8 hexagonal bipyramids, edges with two equivalent Na(2)O8 hexagonal bipyramids, edges with two equivalent Sr(1)O6 octahedra, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Sr(2)O8 hexagonal bipyramid,  a cornercorner with one Sr(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  an edgeedge with one Na(1)O8 hexagonal bipyramid,  an edgeedge with one Na(3)O8 hexagonal bipyramid,  an edgeedge with one Sr(2)O8 hexagonal bipyramid, and edges with two equivalent Na(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 48°. In the second Si site, Si(2) is bonded to one O(2), one O(6), and two equivalent O(4) atoms to form SiO4 tetrahedra that share  a cornercorner with one Na(3)O8 hexagonal bipyramid,  a cornercorner with one Sr(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Na(1)O8 hexagonal bipyramid, edges with two equivalent Na(2)O8 hexagonal bipyramids, and edges with two equivalent Sr(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 51°. There are six inequivalent O sites. In the first O site, O(3) is bonded in a 2-coordinate geometry to one Na(3), two equivalent Na(2), and two equivalent Si(1) atoms. In the second O site, O(4) is bonded in a 2-coordinate geometry to one Na(1), one Na(2), one Sr(2), one Si(1), and one Si(2) atom. In the third O site, O(5) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), one Na(4), one Sr(2), and one Si(1) atom. In the fourth O site, O(6) is bonded in a 5-coordinate geometry to one Na(3), one Na(4), two equivalent Na(2), and one Si(2) atom. In the fifth O site, O(1) is bonded in a 5-coordinate geometry to one Na(3), one Na(4), one Sr(1), one Sr(2), and one Si(1) atom. In the sixth O site, O(2) is bonded in a 5-coordinate geometry to one Na(4), one Sr(1), two equivalent Sr(2), and one Si(2) atom. is represented by the CIF card [CIF]
data_Na2Sr(SiO3)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.760
_cell_length_b   7.760
_cell_length_c   7.757
_cell_angle_alpha   88.418
_cell_angle_beta   88.418
_cell_angle_gamma   89.366
_symmetry_Int_Tables_number   1
_cell_volume   466.705
_cell_formula_units_Z   3
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  0.500  0.500  0.000  1.0
  Na  Na1  1  0.500  0.000  0.500  1.0
  Na  Na2  1  0.000  0.500  0.500  1.0
  Na  Na3  1  0.000  0.000  0.500  1.0
  Na  Na4  1  0.253  0.253  0.268  1.0
  Na  Na5  1  0.747  0.747  0.732  1.0
  Sr  Sr6  1  0.000  0.000  0.000  1.0
  Sr  Sr7  1  0.000  0.500  0.000  1.0
  Sr  Sr8  1  0.500  0.000  0.000  1.0
  Si  Si9  1  0.260  0.712  0.712  1.0
  Si  Si10  1  0.714  0.714  0.264  1.0
  Si  Si11  1  0.712  0.260  0.712  1.0
  Si  Si12  1  0.740  0.288  0.288  1.0
  Si  Si13  1  0.286  0.286  0.736  1.0
  Si  Si14  1  0.288  0.740  0.288  1.0
  O  O15  1  0.076  0.774  0.793  1.0
  O  O16  1  0.782  0.782  0.075  1.0
  O  O17  1  0.774  0.076  0.793  1.0
  O  O18  1  0.924  0.226  0.207  1.0
  O  O19  1  0.218  0.218  0.925  1.0
  O  O20  1  0.226  0.924  0.207  1.0
  O  O21  1  0.253  0.747  0.500  1.0
  O  O22  1  0.746  0.501  0.253  1.0
  O  O23  1  0.499  0.254  0.747  1.0
  O  O24  1  0.254  0.499  0.747  1.0
  O  O25  1  0.501  0.746  0.253  1.0
  O  O26  1  0.747  0.253  0.500  1.0
  O  O27  1  0.437  0.786  0.783  1.0
  O  O28  1  0.788  0.788  0.437  1.0
  O  O29  1  0.786  0.437  0.783  1.0
  O  O30  1  0.563  0.214  0.217  1.0
  O  O31  1  0.212  0.212  0.563  1.0
  O  O32  1  0.214  0.563  0.217  1.0
[/CIF]
.
The material described by Na2SrSi2O6 crystallizes in the monoclinic C2/m space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to four equivalent O(4) and four equivalent O(5) atoms to form distorted NaO8 hexagonal bipyramids that share corners with eight equivalent Na(2)O8 hexagonal bipyramids, edges with four equivalent Sr(2)O8 hexagonal bipyramids, edges with two equivalent Si(2)O4 tetrahedra, and edges with four equivalent Si(1)O4 tetrahedra. In the second Na site, Na(2) is bonded to two equivalent O(3), two equivalent O(4), two equivalent O(5), and two equivalent O(6) atoms to form distorted NaO8 hexagonal bipyramids that share corners with four equivalent Na(1)O8 hexagonal bipyramids, corners with four equivalent Na(2)O8 hexagonal bipyramids, edges with two equivalent Na(3)O8 hexagonal bipyramids, edges with two equivalent Sr(2)O8 hexagonal bipyramids, edges with two equivalent Si(2)O4 tetrahedra, and edges with four equivalent Si(1)O4 tetrahedra. In the third Na site, Na(3) is bonded to two equivalent O(3), two equivalent O(6), and four equivalent O(1) atoms to form distorted NaO8 hexagonal bipyramids that share corners with four equivalent Sr(2)O8 hexagonal bipyramids, corners with two equivalent Si(2)O4 tetrahedra, edges with four equivalent Na(2)O8 hexagonal bipyramids, edges with two equivalent Sr(1)O6 octahedra, and edges with four equivalent Si(1)O4 tetrahedra. In the fourth Na site, Na(4) is bonded in a 6-coordinate geometry to one O(2), one O(6), two equivalent O(1), and two equivalent O(5) atoms. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form SrO6 octahedra that share corners with two equivalent Si(2)O4 tetrahedra, corners with four equivalent Si(1)O4 tetrahedra, edges with two equivalent Na(3)O8 hexagonal bipyramids, and edges with four equivalent Sr(2)O8 hexagonal bipyramids. In the second Sr site, Sr(2) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form SrO8 hexagonal bipyramids that share corners with two equivalent Na(3)O8 hexagonal bipyramids, corners with two equivalent Sr(2)O8 hexagonal bipyramids, corners with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Na(1)O8 hexagonal bipyramids, edges with two equivalent Na(2)O8 hexagonal bipyramids, edges with two equivalent Sr(1)O6 octahedra, edges with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Sr(2)O8 hexagonal bipyramid,  a cornercorner with one Sr(1)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra,  an edgeedge with one Na(1)O8 hexagonal bipyramid,  an edgeedge with one Na(3)O8 hexagonal bipyramid,  an edgeedge with one Sr(2)O8 hexagonal bipyramid, and edges with two equivalent Na(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 48°. In the second Si site, Si(2) is bonded to one O(2), one O(6), and two equivalent O(4) atoms to form SiO4 tetrahedra that share  a cornercorner with one Na(3)O8 hexagonal bipyramid,  a cornercorner with one Sr(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Na(1)O8 hexagonal bipyramid, edges with two equivalent Na(2)O8 hexagonal bipyramids, and edges with two equivalent Sr(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 51°. There are six inequivalent O sites. In the first O site, O(3) is bonded in a 2-coordinate geometry to one Na(3), two equivalent Na(2), and two equivalent Si(1) atoms. In the second O site, O(4) is bonded in a 2-coordinate geometry to one Na(1), one Na(2), one Sr(2), one Si(1), and one Si(2) atom. In the third O site, O(5) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), one Na(4), one Sr(2), and one Si(1) atom. In the fourth O site, O(6) is bonded in a 5-coordinate geometry to one Na(3), one Na(4), two equivalent Na(2), and one Si(2) atom. In the fifth O site, O(1) is bonded in a 5-coordinate geometry to one Na(3), one Na(4), one Sr(1), one Sr(2), and one Si(1) atom. In the sixth O site, O(2) is bonded in a 5-coordinate geometry to one Na(4), one Sr(1), two equivalent Sr(2), and one Si(2) atom. is represented by the CIF card [CIF]
data_Na2Sr(SiO3)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.760
_cell_length_b   7.760
_cell_length_c   7.757
_cell_angle_alpha   88.418
_cell_angle_beta   88.418
_cell_angle_gamma   89.366
_symmetry_Int_Tables_number   1
_cell_volume   466.705
_cell_formula_units_Z   3
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  0.500  0.500  0.000  1.0
  Na  Na1  1  0.500  0.000  0.500  1.0
  Na  Na2  1  0.000  0.500  0.500  1.0
  Na  Na3  1  0.000  0.000  0.500  1.0
  Na  Na4  1  0.253  0.253  0.268  1.0
  Na  Na5  1  0.747  0.747  0.732  1.0
  Sr  Sr6  1  0.000  0.000  0.000  1.0
  Sr  Sr7  1  0.000  0.500  0.000  1.0
  Sr  Sr8  1  0.500  0.000  0.000  1.0
  Si  Si9  1  0.260  0.712  0.712  1.0
  Si  Si10  1  0.714  0.714  0.264  1.0
  Si  Si11  1  0.712  0.260  0.712  1.0
  Si  Si12  1  0.740  0.288  0.288  1.0
  Si  Si13  1  0.286  0.286  0.736  1.0
  Si  Si14  1  0.288  0.740  0.288  1.0
  O  O15  1  0.076  0.774  0.793  1.0
  O  O16  1  0.782  0.782  0.075  1.0
  O  O17  1  0.774  0.076  0.793  1.0
  O  O18  1  0.924  0.226  0.207  1.0
  O  O19  1  0.218  0.218  0.925  1.0
  O  O20  1  0.226  0.924  0.207  1.0
  O  O21  1  0.253  0.747  0.500  1.0
  O  O22  1  0.746  0.501  0.253  1.0
  O  O23  1  0.499  0.254  0.747  1.0
  O  O24  1  0.254  0.499  0.747  1.0
  O  O25  1  0.501  0.746  0.253  1.0
  O  O26  1  0.747  0.253  0.500  1.0
  O  O27  1  0.437  0.786  0.783  1.0
  O  O28  1  0.788  0.788  0.437  1.0
  O  O29  1  0.786  0.437  0.783  1.0
  O  O30  1  0.563  0.214  0.217  1.0
  O  O31  1  0.212  0.212  0.563  1.0
  O  O32  1  0.214  0.563  0.217  1.0
[/CIF]
.