The structure described by Ba5Nb2O9(O2) crystallizes in the monoclinic C2/c space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(5), and four equivalent O(4) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(1)O12 cuboctahedra and faces with six equivalent Nb(1)O6 octahedra. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and three equivalent O(6) atoms. In the third Ba site, Ba(3) is bonded in a 11-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. Nb(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form NbO6 octahedra that share faces with three equivalent Ba(1)O12 cuboctahedra and  a faceface with one Nb(1)O6 octahedra. There are six inequivalent O sites. In the first O site, O(4) is bonded to two equivalent Ba(1), two equivalent Ba(3), and two equivalent Nb(1) atoms to form a mixture of distorted corner and face-sharing OBa4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 8-60°. In the second O site, O(5) is bonded to two equivalent Ba(1), two equivalent Ba(3), and two equivalent Nb(1) atoms to form a mixture of distorted corner and face-sharing OBa4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 7-60°. In the third O site, O(6) is bonded in a 6-coordinate geometry to two equivalent Ba(3), three equivalent Ba(2), and one O(6) atom. In the fourth O site, O(1) is bonded in a 6-coordinate geometry to one Ba(1), two equivalent Ba(2), two equivalent Ba(3), and one Nb(1) atom. In the fifth O site, O(2) is bonded in a 6-coordinate geometry to one Ba(1), two equivalent Ba(2), two equivalent Ba(3), and one Nb(1) atom. In the sixth O site, O(3) is bonded in a 6-coordinate geometry to one Ba(1), two equivalent Ba(2), two equivalent Ba(3), and one Nb(1) atom. is represented by the CIF file [CIF]
data_Ba5Nb2O11
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.138
_cell_length_b   6.138
_cell_length_c   18.620
_cell_angle_alpha   89.716
_cell_angle_beta   89.716
_cell_angle_gamma   119.970
_symmetry_Int_Tables_number   1
_cell_volume   607.755
_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  0.667  0.333  0.750  1.0
  Ba  Ba1  1  0.333  0.667  0.250  1.0
  Ba  Ba2  1  0.656  0.328  0.978  1.0
  Ba  Ba3  1  0.344  0.672  0.022  1.0
  Ba  Ba4  1  0.328  0.656  0.478  1.0
  Ba  Ba5  1  0.672  0.344  0.522  1.0
  Ba  Ba6  1  0.003  0.001  0.860  1.0
  Ba  Ba7  1  0.997  0.999  0.140  1.0
  Ba  Ba8  1  0.001  0.003  0.360  1.0
  Ba  Ba9  1  0.999  0.997  0.640  1.0
  Nb  Nb10  1  0.667  0.334  0.330  1.0
  Nb  Nb11  1  0.333  0.666  0.670  1.0
  Nb  Nb12  1  0.334  0.667  0.830  1.0
  Nb  Nb13  1  0.666  0.333  0.170  1.0
  O  O14  1  0.983  0.491  0.379  1.0
  O  O15  1  0.510  0.019  0.383  1.0
  O  O16  1  0.508  0.491  0.379  1.0
  O  O17  1  0.017  0.509  0.621  1.0
  O  O18  1  0.490  0.981  0.617  1.0
  O  O19  1  0.492  0.509  0.621  1.0
  O  O20  1  0.019  0.510  0.883  1.0
  O  O21  1  0.491  0.983  0.879  1.0
  O  O22  1  0.491  0.508  0.879  1.0
  O  O23  1  0.981  0.490  0.117  1.0
  O  O24  1  0.509  0.017  0.121  1.0
  O  O25  1  0.509  0.492  0.121  1.0
  O  O26  1  0.372  0.185  0.251  1.0
  O  O27  1  0.815  0.628  0.249  1.0
  O  O28  1  0.815  0.185  0.250  1.0
  O  O29  1  0.628  0.815  0.749  1.0
  O  O30  1  0.185  0.372  0.751  1.0
  O  O31  1  0.185  0.815  0.750  1.0
  O  O32  1  0.143  0.071  0.001  1.0
  O  O33  1  0.857  0.929  0.999  1.0
  O  O34  1  0.071  0.143  0.501  1.0
  O  O35  1  0.929  0.857  0.499  1.0
[/CIF]
.
The structure described by Ba5Nb2O9(O2) crystallizes in the monoclinic C2/c space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(5), and four equivalent O(4) atoms to form BaO12 cuboctahedra that share corners with six equivalent Ba(1)O12 cuboctahedra and faces with six equivalent Nb(1)O6 octahedra. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and three equivalent O(6) atoms. In the third Ba site, Ba(3) is bonded in a 11-coordinate geometry to one O(5), two equivalent O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. Nb(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form NbO6 octahedra that share faces with three equivalent Ba(1)O12 cuboctahedra and  a faceface with one Nb(1)O6 octahedra. There are six inequivalent O sites. In the first O site, O(4) is bonded to two equivalent Ba(1), two equivalent Ba(3), and two equivalent Nb(1) atoms to form a mixture of distorted corner and face-sharing OBa4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 8-60°. In the second O site, O(5) is bonded to two equivalent Ba(1), two equivalent Ba(3), and two equivalent Nb(1) atoms to form a mixture of distorted corner and face-sharing OBa4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 7-60°. In the third O site, O(6) is bonded in a 6-coordinate geometry to two equivalent Ba(3), three equivalent Ba(2), and one O(6) atom. In the fourth O site, O(1) is bonded in a 6-coordinate geometry to one Ba(1), two equivalent Ba(2), two equivalent Ba(3), and one Nb(1) atom. In the fifth O site, O(2) is bonded in a 6-coordinate geometry to one Ba(1), two equivalent Ba(2), two equivalent Ba(3), and one Nb(1) atom. In the sixth O site, O(3) is bonded in a 6-coordinate geometry to one Ba(1), two equivalent Ba(2), two equivalent Ba(3), and one Nb(1) atom. is represented by the CIF file [CIF]
data_Ba5Nb2O11
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.138
_cell_length_b   6.138
_cell_length_c   18.620
_cell_angle_alpha   89.716
_cell_angle_beta   89.716
_cell_angle_gamma   119.970
_symmetry_Int_Tables_number   1
_cell_volume   607.755
_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  0.667  0.333  0.750  1.0
  Ba  Ba1  1  0.333  0.667  0.250  1.0
  Ba  Ba2  1  0.656  0.328  0.978  1.0
  Ba  Ba3  1  0.344  0.672  0.022  1.0
  Ba  Ba4  1  0.328  0.656  0.478  1.0
  Ba  Ba5  1  0.672  0.344  0.522  1.0
  Ba  Ba6  1  0.003  0.001  0.860  1.0
  Ba  Ba7  1  0.997  0.999  0.140  1.0
  Ba  Ba8  1  0.001  0.003  0.360  1.0
  Ba  Ba9  1  0.999  0.997  0.640  1.0
  Nb  Nb10  1  0.667  0.334  0.330  1.0
  Nb  Nb11  1  0.333  0.666  0.670  1.0
  Nb  Nb12  1  0.334  0.667  0.830  1.0
  Nb  Nb13  1  0.666  0.333  0.170  1.0
  O  O14  1  0.983  0.491  0.379  1.0
  O  O15  1  0.510  0.019  0.383  1.0
  O  O16  1  0.508  0.491  0.379  1.0
  O  O17  1  0.017  0.509  0.621  1.0
  O  O18  1  0.490  0.981  0.617  1.0
  O  O19  1  0.492  0.509  0.621  1.0
  O  O20  1  0.019  0.510  0.883  1.0
  O  O21  1  0.491  0.983  0.879  1.0
  O  O22  1  0.491  0.508  0.879  1.0
  O  O23  1  0.981  0.490  0.117  1.0
  O  O24  1  0.509  0.017  0.121  1.0
  O  O25  1  0.509  0.492  0.121  1.0
  O  O26  1  0.372  0.185  0.251  1.0
  O  O27  1  0.815  0.628  0.249  1.0
  O  O28  1  0.815  0.185  0.250  1.0
  O  O29  1  0.628  0.815  0.749  1.0
  O  O30  1  0.185  0.372  0.751  1.0
  O  O31  1  0.185  0.815  0.750  1.0
  O  O32  1  0.143  0.071  0.001  1.0
  O  O33  1  0.857  0.929  0.999  1.0
  O  O34  1  0.071  0.143  0.501  1.0
  O  O35  1  0.929  0.857  0.499  1.0
[/CIF]
.