The structure described by Na2BaTi2(Si2O7)2 crystallizes in the orthorhombic Ima2 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 9-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(3), and four equivalent O(4) atoms. Ba(1) is bonded to one O(2), one O(5), two equivalent O(6), four equivalent O(7), and four equivalent O(8) atoms to form distorted BaO12 cuboctahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, edges with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Si(2)O4 tetrahedra, faces with two equivalent Ba(1)O12 cuboctahedra, and faces with two equivalent Ti(1)O6 octahedra. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(2), one O(5), two equivalent O(1), and two equivalent O(8) atoms to form distorted TiO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and faces with two equivalent Ba(1)O12 cuboctahedra. In the second Ti site, Ti(2) is bonded in a 6-coordinate geometry to one O(2), one O(5), two equivalent O(3), and two equivalent O(7) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ba(1)O12 cuboctahedra, corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 28-45°. In the second Si site, Si(2) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ba(1)O12 cuboctahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Ba(1)O12 cuboctahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Ti(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ba(1), one Ti(1), and one Ti(2) atom. In the third O site, O(3) is bonded to one Na(1), one Na(2), one Ti(2), and one Si(2) atom to form a mixture of distorted corner and edge-sharing ONa2TiSi trigonal pyramids. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Na(2), one Si(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Na(2), two equivalent Na(1), one Ba(1), one Ti(1), and one Ti(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Ba(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Ti(2), and one Si(2) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Ti(1), and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_BaNa2Ti2(Si2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.698
_cell_length_b   9.698
_cell_length_c   9.698
_cell_angle_alpha   129.873
_cell_angle_beta   114.192
_cell_angle_gamma   87.084
_symmetry_Int_Tables_number   1
_cell_volume   608.680
_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
  Ba  Ba0  1  0.001  0.728  0.227  1.0
  Ba  Ba1  1  0.999  0.226  0.727  1.0
  Na  Na2  1  0.000  0.978  0.978  1.0
  Na  Na3  1  0.593  0.812  0.719  1.0
  Na  Na4  1  0.407  0.126  0.219  1.0
  Na  Na5  1  0.500  0.978  0.478  1.0
  Ti  Ti6  1  0.218  0.172  0.454  1.0
  Ti  Ti7  1  0.782  0.236  0.954  1.0
  Ti  Ti8  1  0.781  0.737  0.456  1.0
  Ti  Ti9  1  0.219  0.675  0.956  1.0
  Si  Si10  1  0.616  0.432  0.758  1.0
  Si  Si11  1  0.826  0.537  0.653  1.0
  Si  Si12  1  0.174  0.827  0.711  1.0
  Si  Si13  1  0.174  0.432  0.316  1.0
  Si  Si14  1  0.616  0.827  0.153  1.0
  Si  Si15  1  0.384  0.142  0.816  1.0
  Si  Si16  1  0.384  0.537  0.211  1.0
  Si  Si17  1  0.826  0.142  0.258  1.0
  O  O18  1  0.183  0.266  0.317  1.0
  O  O19  1  0.216  0.463  0.747  1.0
  O  O20  1  0.449  0.266  0.583  1.0
  O  O21  1  0.551  0.134  0.817  1.0
  O  O22  1  0.185  0.831  0.885  1.0
  O  O23  1  0.815  0.700  0.646  1.0
  O  O24  1  0.662  0.487  0.648  1.0
  O  O25  1  0.797  0.041  0.745  1.0
  O  O26  1  0.821  0.342  0.449  1.0
  O  O27  1  0.019  0.879  0.622  1.0
  O  O28  1  0.607  0.627  0.949  1.0
  O  O29  1  0.981  0.602  0.860  1.0
  O  O30  1  0.243  0.602  0.122  1.0
  O  O31  1  0.446  0.831  0.146  1.0
  O  O32  1  0.240  0.092  0.613  1.0
  O  O33  1  0.980  0.092  0.352  1.0
  O  O34  1  0.661  0.986  0.148  1.0
  O  O35  1  0.179  0.627  0.521  1.0
  O  O36  1  0.393  0.342  0.021  1.0
  O  O37  1  0.020  0.372  0.113  1.0
  O  O38  1  0.817  0.134  0.083  1.0
  O  O39  1  0.784  0.531  0.247  1.0
  O  O40  1  0.760  0.372  0.852  1.0
  O  O41  1  0.757  0.879  0.360  1.0
  O  O42  1  0.554  0.700  0.385  1.0
  O  O43  1  0.338  0.986  0.825  1.0
  O  O44  1  0.339  0.487  0.325  1.0
  O  O45  1  0.203  0.948  0.245  1.0
[/CIF]
.
The structure described by Na2BaTi2(Si2O7)2 crystallizes in the orthorhombic Ima2 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 9-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(3), and four equivalent O(4) atoms. Ba(1) is bonded to one O(2), one O(5), two equivalent O(6), four equivalent O(7), and four equivalent O(8) atoms to form distorted BaO12 cuboctahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, edges with two equivalent Si(1)O4 tetrahedra, edges with two equivalent Si(2)O4 tetrahedra, faces with two equivalent Ba(1)O12 cuboctahedra, and faces with two equivalent Ti(1)O6 octahedra. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(2), one O(5), two equivalent O(1), and two equivalent O(8) atoms to form distorted TiO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and faces with two equivalent Ba(1)O12 cuboctahedra. In the second Ti site, Ti(2) is bonded in a 6-coordinate geometry to one O(2), one O(5), two equivalent O(3), and two equivalent O(7) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(4), one O(6), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ba(1)O12 cuboctahedra, corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent Si(2)O4 tetrahedra, and  an edgeedge with one Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 28-45°. In the second Si site, Si(2) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Ba(1)O12 cuboctahedra, corners with two equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Ba(1)O12 cuboctahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Ti(1), and one Si(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Ba(1), one Ti(1), and one Ti(2) atom. In the third O site, O(3) is bonded to one Na(1), one Na(2), one Ti(2), and one Si(2) atom to form a mixture of distorted corner and edge-sharing ONa2TiSi trigonal pyramids. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Na(2), one Si(1), and one Si(2) atom. In the fifth O site, O(5) is bonded in a distorted single-bond geometry to one Na(2), two equivalent Na(1), one Ba(1), one Ti(1), and one Ti(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Ba(1), one Si(1), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Ti(2), and one Si(2) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Ti(1), and one Si(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_BaNa2Ti2(Si2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.698
_cell_length_b   9.698
_cell_length_c   9.698
_cell_angle_alpha   129.873
_cell_angle_beta   114.192
_cell_angle_gamma   87.084
_symmetry_Int_Tables_number   1
_cell_volume   608.680
_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
  Ba  Ba0  1  0.001  0.728  0.227  1.0
  Ba  Ba1  1  0.999  0.226  0.727  1.0
  Na  Na2  1  0.000  0.978  0.978  1.0
  Na  Na3  1  0.593  0.812  0.719  1.0
  Na  Na4  1  0.407  0.126  0.219  1.0
  Na  Na5  1  0.500  0.978  0.478  1.0
  Ti  Ti6  1  0.218  0.172  0.454  1.0
  Ti  Ti7  1  0.782  0.236  0.954  1.0
  Ti  Ti8  1  0.781  0.737  0.456  1.0
  Ti  Ti9  1  0.219  0.675  0.956  1.0
  Si  Si10  1  0.616  0.432  0.758  1.0
  Si  Si11  1  0.826  0.537  0.653  1.0
  Si  Si12  1  0.174  0.827  0.711  1.0
  Si  Si13  1  0.174  0.432  0.316  1.0
  Si  Si14  1  0.616  0.827  0.153  1.0
  Si  Si15  1  0.384  0.142  0.816  1.0
  Si  Si16  1  0.384  0.537  0.211  1.0
  Si  Si17  1  0.826  0.142  0.258  1.0
  O  O18  1  0.183  0.266  0.317  1.0
  O  O19  1  0.216  0.463  0.747  1.0
  O  O20  1  0.449  0.266  0.583  1.0
  O  O21  1  0.551  0.134  0.817  1.0
  O  O22  1  0.185  0.831  0.885  1.0
  O  O23  1  0.815  0.700  0.646  1.0
  O  O24  1  0.662  0.487  0.648  1.0
  O  O25  1  0.797  0.041  0.745  1.0
  O  O26  1  0.821  0.342  0.449  1.0
  O  O27  1  0.019  0.879  0.622  1.0
  O  O28  1  0.607  0.627  0.949  1.0
  O  O29  1  0.981  0.602  0.860  1.0
  O  O30  1  0.243  0.602  0.122  1.0
  O  O31  1  0.446  0.831  0.146  1.0
  O  O32  1  0.240  0.092  0.613  1.0
  O  O33  1  0.980  0.092  0.352  1.0
  O  O34  1  0.661  0.986  0.148  1.0
  O  O35  1  0.179  0.627  0.521  1.0
  O  O36  1  0.393  0.342  0.021  1.0
  O  O37  1  0.020  0.372  0.113  1.0
  O  O38  1  0.817  0.134  0.083  1.0
  O  O39  1  0.784  0.531  0.247  1.0
  O  O40  1  0.760  0.372  0.852  1.0
  O  O41  1  0.757  0.879  0.360  1.0
  O  O42  1  0.554  0.700  0.385  1.0
  O  O43  1  0.338  0.986  0.825  1.0
  O  O44  1  0.339  0.487  0.325  1.0
  O  O45  1  0.203  0.948  0.245  1.0
[/CIF]
.