The structure described by Ba2Nb5O9 crystallizes in the tetragonal P4/mmm space group. Ba(1) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with eight equivalent Ba(1)O12 cuboctahedra, faces with five equivalent Ba(1)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Nb(2)O5 square pyramids. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O5 square pyramids, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. In the second Nb site, Nb(2) is bonded to one O(2) and four equivalent O(3) atoms to form NbO5 square pyramids that share  a cornercorner with one Nb(1)O6 octahedra, corners with four equivalent Nb(2)O5 square pyramids, and faces with four equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. In the third Nb site, Nb(3) is bonded in a square co-planar geometry to two equivalent O(3) and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to four equivalent Ba(1) and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to four equivalent Ba(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded to two equivalent Ba(1), one Nb(3), and two equivalent Nb(2) atoms to form a mixture of distorted edge and corner-sharing OBa2Nb3 trigonal bipyramids. In the fourth O site, O(4) is bonded in a square co-planar geometry to four equivalent Nb(3) atoms. is represented by the CIF file [CIF]
data_Ba2Nb5O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.212
_cell_length_b   4.212
_cell_length_c   12.337
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   218.824
_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
  Ba  Ba0  1  0.000  0.000  0.831  1.0
  Ba  Ba1  1  0.000  0.000  0.169  1.0
  Nb  Nb2  1  0.500  0.500  0.000  1.0
  Nb  Nb3  1  0.500  0.500  0.662  1.0
  Nb  Nb4  1  0.500  0.500  0.338  1.0
  Nb  Nb5  1  0.500  0.000  0.500  1.0
  Nb  Nb6  1  0.000  0.500  0.500  1.0
  O  O7  1  0.000  0.500  0.000  1.0
  O  O8  1  0.500  0.000  0.000  1.0
  O  O9  1  0.500  0.500  0.839  1.0
  O  O10  1  0.500  0.500  0.161  1.0
  O  O11  1  0.000  0.500  0.673  1.0
  O  O12  1  0.500  0.000  0.673  1.0
  O  O13  1  0.000  0.500  0.327  1.0
  O  O14  1  0.000  0.000  0.500  1.0
  O  O15  1  0.500  0.000  0.327  1.0
[/CIF]
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The structure described by Ba2Nb5O9 crystallizes in the tetragonal P4/mmm space group. Ba(1) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with eight equivalent Ba(1)O12 cuboctahedra, faces with five equivalent Ba(1)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Nb(2)O5 square pyramids. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O5 square pyramids, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. In the second Nb site, Nb(2) is bonded to one O(2) and four equivalent O(3) atoms to form NbO5 square pyramids that share  a cornercorner with one Nb(1)O6 octahedra, corners with four equivalent Nb(2)O5 square pyramids, and faces with four equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. In the third Nb site, Nb(3) is bonded in a square co-planar geometry to two equivalent O(3) and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to four equivalent Ba(1) and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to four equivalent Ba(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded to two equivalent Ba(1), one Nb(3), and two equivalent Nb(2) atoms to form a mixture of distorted edge and corner-sharing OBa2Nb3 trigonal bipyramids. In the fourth O site, O(4) is bonded in a square co-planar geometry to four equivalent Nb(3) atoms. is represented by the CIF file [CIF]
data_Ba2Nb5O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.212
_cell_length_b   4.212
_cell_length_c   12.337
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   218.824
_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
  Ba  Ba0  1  0.000  0.000  0.831  1.0
  Ba  Ba1  1  0.000  0.000  0.169  1.0
  Nb  Nb2  1  0.500  0.500  0.000  1.0
  Nb  Nb3  1  0.500  0.500  0.662  1.0
  Nb  Nb4  1  0.500  0.500  0.338  1.0
  Nb  Nb5  1  0.500  0.000  0.500  1.0
  Nb  Nb6  1  0.000  0.500  0.500  1.0
  O  O7  1  0.000  0.500  0.000  1.0
  O  O8  1  0.500  0.000  0.000  1.0
  O  O9  1  0.500  0.500  0.839  1.0
  O  O10  1  0.500  0.500  0.161  1.0
  O  O11  1  0.000  0.500  0.673  1.0
  O  O12  1  0.500  0.000  0.673  1.0
  O  O13  1  0.000  0.500  0.327  1.0
  O  O14  1  0.000  0.000  0.500  1.0
  O  O15  1  0.500  0.000  0.327  1.0
[/CIF]
.