The structure described by Na6Ti2O7 crystallizes in the monoclinic C2/m space group. There are five inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted T-shaped geometry to one O(1), one O(3), and one O(7) atom. In the second Na site, Na(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form distorted NaO4 tetrahedra that share  a cornercorner with one Na(3)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra,  a cornercorner with one Ti(3)O4 tetrahedra, corners with two equivalent Ti(1)O4 tetrahedra, and  an edgeedge with one Na(2)O4 tetrahedra. In the third Na site, Na(3) is bonded to one O(1), one O(4), and two equivalent O(7) atoms to form distorted NaO4 tetrahedra that share  a cornercorner with one Na(2)O4 tetrahedra,  a cornercorner with one Na(3)O4 tetrahedra,  a cornercorner with one Ti(1)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra, corners with two equivalent Ti(3)O4 tetrahedra, and  an edgeedge with one Na(3)O4 tetrahedra. In the fourth Na site, Na(4) is bonded in a linear geometry to one O(2) and one O(6) atom. In the fifth Na site, Na(5) is bonded in a distorted trigonal planar geometry to one O(4) and two equivalent O(5) atoms. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(2), and two equivalent O(5) atoms to form TiO4 tetrahedra that share corners with two equivalent Na(3)O4 tetrahedra and corners with four equivalent Na(2)O4 tetrahedra. In the second Ti site, Ti(2) is bonded to one O(3), one O(8), and two equivalent O(4) atoms to form TiO4 tetrahedra that share  a cornercorner with one Ti(2)O4 tetrahedra,  a cornercorner with one Ti(3)O4 tetrahedra, corners with two equivalent Na(2)O4 tetrahedra, and corners with two equivalent Na(3)O4 tetrahedra. In the third Ti site, Ti(3) is bonded to one O(3), one O(6), and two equivalent O(7) atoms to form TiO4 tetrahedra that share  a cornercorner with one Ti(2)O4 tetrahedra, corners with two equivalent Na(2)O4 tetrahedra, and corners with four equivalent Na(3)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Na(1), two equivalent Na(3), and one Ti(1) atom. In the second O site, O(2) is bonded to one Na(4), two equivalent Na(2), and one Ti(1) atom to form a mixture of distorted corner and edge-sharing ONa3Ti tetrahedra. In the third O site, O(3) is bonded to two equivalent Na(1), one Ti(2), and one Ti(3) atom to form distorted corner-sharing ONa2Ti2 tetrahedra. In the fourth O site, O(4) is bonded to one Na(2), one Na(3), one Na(5), and one Ti(2) atom to form ONa3Ti tetrahedra that share  a cornercorner with one O(3)Na2Ti2 tetrahedra,  a cornercorner with one O(2)Na3Ti tetrahedra,  a cornercorner with one O(4)Na3Ti tetrahedra,  a cornercorner with one O(6)Na3Ti tetrahedra, corners with two equivalent O(7)Na3Ti tetrahedra, and corners with three equivalent O(5)Na3Ti tetrahedra. In the fifth O site, O(5) is bonded to one Na(2), two equivalent Na(5), and one Ti(1) atom to form a mixture of distorted corner and edge-sharing ONa3Ti tetrahedra. In the sixth O site, O(6) is bonded to one Na(4), two equivalent Na(2), and one Ti(3) atom to form distorted ONa3Ti tetrahedra that share  a cornercorner with one O(3)Na2Ti2 tetrahedra,  a cornercorner with one O(2)Na3Ti tetrahedra, corners with two equivalent O(4)Na3Ti tetrahedra, corners with two equivalent O(5)Na3Ti tetrahedra, corners with two equivalent O(7)Na3Ti tetrahedra, and  an edgeedge with one O(2)Na3Ti tetrahedra. In the seventh O site, O(7) is bonded to one Na(1), two equivalent Na(3), and one Ti(3) atom to form distorted ONa3Ti tetrahedra that share  a cornercorner with one O(6)Na3Ti tetrahedra,  a cornercorner with one O(7)Na3Ti tetrahedra, corners with two equivalent O(3)Na2Ti2 tetrahedra, corners with two equivalent O(4)Na3Ti tetrahedra, and  an edgeedge with one O(7)Na3Ti tetrahedra. In the eighth O site, O(8) is bonded in a linear geometry to two equivalent Ti(2) atoms. is represented by the CIF file [CIF]
data_Na6Ti2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.478
_cell_length_b   8.478
_cell_length_c   11.179
_cell_angle_alpha   76.910
_cell_angle_beta   76.910
_cell_angle_gamma   72.320
_symmetry_Int_Tables_number   1
_cell_volume   734.890
_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  0.975  0.663  0.884  1.0
  Na  Na1  1  0.663  0.975  0.884  1.0
  Na  Na2  1  0.871  0.564  0.380  1.0
  Na  Na3  1  0.564  0.871  0.380  1.0
  Na  Na4  1  0.421  0.749  0.879  1.0
  Na  Na5  1  0.749  0.421  0.879  1.0
  Na  Na6  1  0.540  0.540  0.622  1.0
  Na  Na7  1  0.870  0.194  0.618  1.0
  Na  Na8  1  0.194  0.870  0.618  1.0
  Na  Na9  1  0.130  0.806  0.382  1.0
  Na  Na10  1  0.806  0.130  0.382  1.0
  Na  Na11  1  0.460  0.460  0.378  1.0
  Na  Na12  1  0.579  0.251  0.120  1.0
  Na  Na13  1  0.251  0.579  0.120  1.0
  Na  Na14  1  0.129  0.436  0.620  1.0
  Na  Na15  1  0.436  0.129  0.620  1.0
  Na  Na16  1  0.337  0.025  0.116  1.0
  Na  Na17  1  0.025  0.337  0.116  1.0
  Ti  Ti18  1  0.794  0.794  0.628  1.0
  Ti  Ti19  1  0.888  0.888  0.140  1.0
  Ti  Ti20  1  0.645  0.645  0.129  1.0
  Ti  Ti21  1  0.355  0.355  0.871  1.0
  Ti  Ti22  1  0.112  0.112  0.860  1.0
  Ti  Ti23  1  0.206  0.206  0.372  1.0
  O  O24  1  0.726  0.726  0.797  1.0
  O  O25  1  0.701  0.701  0.539  1.0
  O  O26  1  0.788  0.788  0.054  1.0
  O  O27  1  0.264  0.973  0.763  1.0
  O  O28  1  0.973  0.264  0.763  1.0
  O  O29  1  0.974  0.276  0.412  1.0
  O  O30  1  0.276  0.974  0.412  1.0
  O  O31  1  0.623  0.623  0.297  1.0
  O  O32  1  0.746  0.441  0.083  1.0
  O  O33  1  0.441  0.746  0.083  1.0
  O  O34  1  0.254  0.559  0.917  1.0
  O  O35  1  0.559  0.254  0.917  1.0
  O  O36  1  0.377  0.377  0.703  1.0
  O  O37  1  0.724  0.026  0.588  1.0
  O  O38  1  0.026  0.724  0.588  1.0
  O  O39  1  0.000  0.000  0.000  1.0
  O  O40  1  0.027  0.736  0.237  1.0
  O  O41  1  0.736  0.027  0.237  1.0
  O  O42  1  0.212  0.212  0.946  1.0
  O  O43  1  0.299  0.299  0.461  1.0
  O  O44  1  0.274  0.274  0.203  1.0
[/CIF]
.
The structure described by Na6Ti2O7 crystallizes in the monoclinic C2/m space group. There are five inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted T-shaped geometry to one O(1), one O(3), and one O(7) atom. In the second Na site, Na(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form distorted NaO4 tetrahedra that share  a cornercorner with one Na(3)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra,  a cornercorner with one Ti(3)O4 tetrahedra, corners with two equivalent Ti(1)O4 tetrahedra, and  an edgeedge with one Na(2)O4 tetrahedra. In the third Na site, Na(3) is bonded to one O(1), one O(4), and two equivalent O(7) atoms to form distorted NaO4 tetrahedra that share  a cornercorner with one Na(2)O4 tetrahedra,  a cornercorner with one Na(3)O4 tetrahedra,  a cornercorner with one Ti(1)O4 tetrahedra,  a cornercorner with one Ti(2)O4 tetrahedra, corners with two equivalent Ti(3)O4 tetrahedra, and  an edgeedge with one Na(3)O4 tetrahedra. In the fourth Na site, Na(4) is bonded in a linear geometry to one O(2) and one O(6) atom. In the fifth Na site, Na(5) is bonded in a distorted trigonal planar geometry to one O(4) and two equivalent O(5) atoms. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(2), and two equivalent O(5) atoms to form TiO4 tetrahedra that share corners with two equivalent Na(3)O4 tetrahedra and corners with four equivalent Na(2)O4 tetrahedra. In the second Ti site, Ti(2) is bonded to one O(3), one O(8), and two equivalent O(4) atoms to form TiO4 tetrahedra that share  a cornercorner with one Ti(2)O4 tetrahedra,  a cornercorner with one Ti(3)O4 tetrahedra, corners with two equivalent Na(2)O4 tetrahedra, and corners with two equivalent Na(3)O4 tetrahedra. In the third Ti site, Ti(3) is bonded to one O(3), one O(6), and two equivalent O(7) atoms to form TiO4 tetrahedra that share  a cornercorner with one Ti(2)O4 tetrahedra, corners with two equivalent Na(2)O4 tetrahedra, and corners with four equivalent Na(3)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Na(1), two equivalent Na(3), and one Ti(1) atom. In the second O site, O(2) is bonded to one Na(4), two equivalent Na(2), and one Ti(1) atom to form a mixture of distorted corner and edge-sharing ONa3Ti tetrahedra. In the third O site, O(3) is bonded to two equivalent Na(1), one Ti(2), and one Ti(3) atom to form distorted corner-sharing ONa2Ti2 tetrahedra. In the fourth O site, O(4) is bonded to one Na(2), one Na(3), one Na(5), and one Ti(2) atom to form ONa3Ti tetrahedra that share  a cornercorner with one O(3)Na2Ti2 tetrahedra,  a cornercorner with one O(2)Na3Ti tetrahedra,  a cornercorner with one O(4)Na3Ti tetrahedra,  a cornercorner with one O(6)Na3Ti tetrahedra, corners with two equivalent O(7)Na3Ti tetrahedra, and corners with three equivalent O(5)Na3Ti tetrahedra. In the fifth O site, O(5) is bonded to one Na(2), two equivalent Na(5), and one Ti(1) atom to form a mixture of distorted corner and edge-sharing ONa3Ti tetrahedra. In the sixth O site, O(6) is bonded to one Na(4), two equivalent Na(2), and one Ti(3) atom to form distorted ONa3Ti tetrahedra that share  a cornercorner with one O(3)Na2Ti2 tetrahedra,  a cornercorner with one O(2)Na3Ti tetrahedra, corners with two equivalent O(4)Na3Ti tetrahedra, corners with two equivalent O(5)Na3Ti tetrahedra, corners with two equivalent O(7)Na3Ti tetrahedra, and  an edgeedge with one O(2)Na3Ti tetrahedra. In the seventh O site, O(7) is bonded to one Na(1), two equivalent Na(3), and one Ti(3) atom to form distorted ONa3Ti tetrahedra that share  a cornercorner with one O(6)Na3Ti tetrahedra,  a cornercorner with one O(7)Na3Ti tetrahedra, corners with two equivalent O(3)Na2Ti2 tetrahedra, corners with two equivalent O(4)Na3Ti tetrahedra, and  an edgeedge with one O(7)Na3Ti tetrahedra. In the eighth O site, O(8) is bonded in a linear geometry to two equivalent Ti(2) atoms. is represented by the CIF file [CIF]
data_Na6Ti2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.478
_cell_length_b   8.478
_cell_length_c   11.179
_cell_angle_alpha   76.910
_cell_angle_beta   76.910
_cell_angle_gamma   72.320
_symmetry_Int_Tables_number   1
_cell_volume   734.890
_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  0.975  0.663  0.884  1.0
  Na  Na1  1  0.663  0.975  0.884  1.0
  Na  Na2  1  0.871  0.564  0.380  1.0
  Na  Na3  1  0.564  0.871  0.380  1.0
  Na  Na4  1  0.421  0.749  0.879  1.0
  Na  Na5  1  0.749  0.421  0.879  1.0
  Na  Na6  1  0.540  0.540  0.622  1.0
  Na  Na7  1  0.870  0.194  0.618  1.0
  Na  Na8  1  0.194  0.870  0.618  1.0
  Na  Na9  1  0.130  0.806  0.382  1.0
  Na  Na10  1  0.806  0.130  0.382  1.0
  Na  Na11  1  0.460  0.460  0.378  1.0
  Na  Na12  1  0.579  0.251  0.120  1.0
  Na  Na13  1  0.251  0.579  0.120  1.0
  Na  Na14  1  0.129  0.436  0.620  1.0
  Na  Na15  1  0.436  0.129  0.620  1.0
  Na  Na16  1  0.337  0.025  0.116  1.0
  Na  Na17  1  0.025  0.337  0.116  1.0
  Ti  Ti18  1  0.794  0.794  0.628  1.0
  Ti  Ti19  1  0.888  0.888  0.140  1.0
  Ti  Ti20  1  0.645  0.645  0.129  1.0
  Ti  Ti21  1  0.355  0.355  0.871  1.0
  Ti  Ti22  1  0.112  0.112  0.860  1.0
  Ti  Ti23  1  0.206  0.206  0.372  1.0
  O  O24  1  0.726  0.726  0.797  1.0
  O  O25  1  0.701  0.701  0.539  1.0
  O  O26  1  0.788  0.788  0.054  1.0
  O  O27  1  0.264  0.973  0.763  1.0
  O  O28  1  0.973  0.264  0.763  1.0
  O  O29  1  0.974  0.276  0.412  1.0
  O  O30  1  0.276  0.974  0.412  1.0
  O  O31  1  0.623  0.623  0.297  1.0
  O  O32  1  0.746  0.441  0.083  1.0
  O  O33  1  0.441  0.746  0.083  1.0
  O  O34  1  0.254  0.559  0.917  1.0
  O  O35  1  0.559  0.254  0.917  1.0
  O  O36  1  0.377  0.377  0.703  1.0
  O  O37  1  0.724  0.026  0.588  1.0
  O  O38  1  0.026  0.724  0.588  1.0
  O  O39  1  0.000  0.000  0.000  1.0
  O  O40  1  0.027  0.736  0.237  1.0
  O  O41  1  0.736  0.027  0.237  1.0
  O  O42  1  0.212  0.212  0.946  1.0
  O  O43  1  0.299  0.299  0.461  1.0
  O  O44  1  0.274  0.274  0.203  1.0
[/CIF]
.