The material described by Eu2Nb5O9 crystallizes in the tetragonal P4/mmm space group. Eu(1) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms to form EuO12 cuboctahedra that share corners with eight equivalent Eu(1)O12 cuboctahedra, faces with five equivalent Eu(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(3) 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 Eu(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(1) 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 Eu(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(1) and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Eu(1), one Nb(3), and two equivalent Nb(2) atoms to form a mixture of distorted edge and corner-sharing OEu2Nb3 trigonal bipyramids. In the second O site, O(2) is bonded in a distorted linear geometry to four equivalent Eu(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded in a distorted linear geometry to four equivalent Eu(1) and two equivalent Nb(1) atoms. 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_Eu2Nb5O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.179
_cell_length_b   4.179
_cell_length_c   12.075
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   210.896
_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
  Eu  Eu0  1  0.500  0.500  0.172  1.0
  Eu  Eu1  1  0.500  0.500  0.828  1.0
  Nb  Nb2  1  1.000  0.000  0.000  1.0
  Nb  Nb3  1  1.000  0.000  0.336  1.0
  Nb  Nb4  1  1.000  1.000  0.664  1.0
  Nb  Nb5  1  1.000  0.500  0.500  1.0
  Nb  Nb6  1  0.500  1.000  0.500  1.0
  O  O7  1  1.000  0.500  0.320  1.0
  O  O8  1  1.000  0.500  0.680  1.0
  O  O9  1  0.500  1.000  0.320  1.0
  O  O10  1  0.500  1.000  0.680  1.0
  O  O11  1  1.000  1.000  0.162  1.0
  O  O12  1  0.000  0.000  0.838  1.0
  O  O13  1  1.000  0.500  0.000  1.0
  O  O14  1  0.500  0.000  0.000  1.0
  O  O15  1  0.500  0.500  0.500  1.0
[/CIF]
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The material described by Eu2Nb5O9 crystallizes in the tetragonal P4/mmm space group. Eu(1) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms to form EuO12 cuboctahedra that share corners with eight equivalent Eu(1)O12 cuboctahedra, faces with five equivalent Eu(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(3) 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 Eu(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(1) 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 Eu(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(1) and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Eu(1), one Nb(3), and two equivalent Nb(2) atoms to form a mixture of distorted edge and corner-sharing OEu2Nb3 trigonal bipyramids. In the second O site, O(2) is bonded in a distorted linear geometry to four equivalent Eu(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded in a distorted linear geometry to four equivalent Eu(1) and two equivalent Nb(1) atoms. 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_Eu2Nb5O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.179
_cell_length_b   4.179
_cell_length_c   12.075
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   210.896
_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
  Eu  Eu0  1  0.500  0.500  0.172  1.0
  Eu  Eu1  1  0.500  0.500  0.828  1.0
  Nb  Nb2  1  1.000  0.000  0.000  1.0
  Nb  Nb3  1  1.000  0.000  0.336  1.0
  Nb  Nb4  1  1.000  1.000  0.664  1.0
  Nb  Nb5  1  1.000  0.500  0.500  1.0
  Nb  Nb6  1  0.500  1.000  0.500  1.0
  O  O7  1  1.000  0.500  0.320  1.0
  O  O8  1  1.000  0.500  0.680  1.0
  O  O9  1  0.500  1.000  0.320  1.0
  O  O10  1  0.500  1.000  0.680  1.0
  O  O11  1  1.000  1.000  0.162  1.0
  O  O12  1  0.000  0.000  0.838  1.0
  O  O13  1  1.000  0.500  0.000  1.0
  O  O14  1  0.500  0.000  0.000  1.0
  O  O15  1  0.500  0.500  0.500  1.0
[/CIF]
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