The compound described by Sr4Nb2O9 crystallizes in the orthorhombic Immm space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to two equivalent O(1), two equivalent O(2), four equivalent O(3), and four equivalent O(5) atoms to form distorted SrO12 cuboctahedra that share corners with two equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(3)O6 octahedra, faces with two equivalent Nb(1)O6 octahedra, faces with two equivalent Nb(2)O6 octahedra, and faces with two equivalent Nb(3)O6 octahedra. In the second Sr site, Sr(2) is bonded in a distorted q6 geometry to one O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. In the third Sr site, Sr(3) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form SrO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and faces with two equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-33°. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(1) and four equivalent O(5) atoms to form NbO6 octahedra that share corners with two equivalent Nb(3)O6 octahedra, corners with four equivalent Sr(3)O6 octahedra, and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. In the second Nb site, Nb(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(3)O6 octahedra, corners with four equivalent Sr(3)O6 octahedra, and faces with two equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-33°. In the third Nb site, Nb(3) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1), two equivalent Sr(2), one Nb(1), and one Nb(3) atom to form distorted corner-sharing OSr4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Sr(1), one Sr(3), two equivalent Sr(2), and one Nb(2) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(2), and one Nb(3) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sr(3), two equivalent Sr(2), and one Nb(2) atom. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to one Sr(3), two equivalent Sr(1), two equivalent Sr(2), and one Nb(1) atom. is represented by the CIF file [CIF]
data_Sr4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.730
_cell_length_b   10.730
_cell_length_c   10.730
_cell_angle_alpha   147.496
_cell_angle_beta   134.459
_cell_angle_gamma   57.061
_symmetry_Int_Tables_number   1
_cell_volume   470.304
_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
  Sr  Sr0  1  0.245  0.500  0.745  1.0
  Sr  Sr1  1  0.872  0.140  0.732  1.0
  Sr  Sr2  1  0.593  0.860  0.732  1.0
  Sr  Sr3  1  0.755  0.500  0.255  1.0
  Sr  Sr4  1  0.407  0.140  0.268  1.0
  Sr  Sr5  1  0.128  0.860  0.268  1.0
  Sr  Sr6  1  0.171  0.671  0.500  1.0
  Sr  Sr7  1  0.829  0.329  0.500  1.0
  Nb  Nb8  1  0.000  0.000  0.000  1.0
  Nb  Nb9  1  0.665  0.665  0.000  1.0
  Nb  Nb10  1  0.335  0.335  0.000  1.0
  Nb  Nb11  1  0.500  0.000  0.500  1.0
  O  O12  1  0.252  0.000  0.252  1.0
  O  O13  1  0.859  0.635  0.224  1.0
  O  O14  1  0.589  0.365  0.224  1.0
  O  O15  1  0.576  0.305  0.729  1.0
  O  O16  1  0.273  0.025  0.752  1.0
  O  O17  1  0.923  0.699  0.776  1.0
  O  O18  1  0.424  0.154  0.729  1.0
  O  O19  1  0.077  0.852  0.776  1.0
  O  O20  1  0.727  0.479  0.752  1.0
  O  O21  1  0.748  0.000  0.748  1.0
  O  O22  1  0.411  0.635  0.776  1.0
  O  O23  1  0.141  0.365  0.776  1.0
  O  O24  1  0.424  0.695  0.271  1.0
  O  O25  1  0.077  0.301  0.224  1.0
  O  O26  1  0.727  0.975  0.248  1.0
  O  O27  1  0.576  0.846  0.271  1.0
  O  O28  1  0.273  0.521  0.248  1.0
  O  O29  1  0.923  0.148  0.224  1.0
[/CIF]
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The compound described by Sr4Nb2O9 crystallizes in the orthorhombic Immm space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to two equivalent O(1), two equivalent O(2), four equivalent O(3), and four equivalent O(5) atoms to form distorted SrO12 cuboctahedra that share corners with two equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(1)O12 cuboctahedra, faces with two equivalent Sr(3)O6 octahedra, faces with two equivalent Nb(1)O6 octahedra, faces with two equivalent Nb(2)O6 octahedra, and faces with two equivalent Nb(3)O6 octahedra. In the second Sr site, Sr(2) is bonded in a distorted q6 geometry to one O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. In the third Sr site, Sr(3) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form SrO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and faces with two equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-33°. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(1) and four equivalent O(5) atoms to form NbO6 octahedra that share corners with two equivalent Nb(3)O6 octahedra, corners with four equivalent Sr(3)O6 octahedra, and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. In the second Nb site, Nb(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(3)O6 octahedra, corners with four equivalent Sr(3)O6 octahedra, and faces with two equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-33°. In the third Nb site, Nb(3) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and faces with four equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1), two equivalent Sr(2), one Nb(1), and one Nb(3) atom to form distorted corner-sharing OSr4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Sr(1), one Sr(3), two equivalent Sr(2), and one Nb(2) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(2), and one Nb(3) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sr(3), two equivalent Sr(2), and one Nb(2) atom. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to one Sr(3), two equivalent Sr(1), two equivalent Sr(2), and one Nb(1) atom. is represented by the CIF file [CIF]
data_Sr4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   10.730
_cell_length_b   10.730
_cell_length_c   10.730
_cell_angle_alpha   147.496
_cell_angle_beta   134.459
_cell_angle_gamma   57.061
_symmetry_Int_Tables_number   1
_cell_volume   470.304
_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
  Sr  Sr0  1  0.245  0.500  0.745  1.0
  Sr  Sr1  1  0.872  0.140  0.732  1.0
  Sr  Sr2  1  0.593  0.860  0.732  1.0
  Sr  Sr3  1  0.755  0.500  0.255  1.0
  Sr  Sr4  1  0.407  0.140  0.268  1.0
  Sr  Sr5  1  0.128  0.860  0.268  1.0
  Sr  Sr6  1  0.171  0.671  0.500  1.0
  Sr  Sr7  1  0.829  0.329  0.500  1.0
  Nb  Nb8  1  0.000  0.000  0.000  1.0
  Nb  Nb9  1  0.665  0.665  0.000  1.0
  Nb  Nb10  1  0.335  0.335  0.000  1.0
  Nb  Nb11  1  0.500  0.000  0.500  1.0
  O  O12  1  0.252  0.000  0.252  1.0
  O  O13  1  0.859  0.635  0.224  1.0
  O  O14  1  0.589  0.365  0.224  1.0
  O  O15  1  0.576  0.305  0.729  1.0
  O  O16  1  0.273  0.025  0.752  1.0
  O  O17  1  0.923  0.699  0.776  1.0
  O  O18  1  0.424  0.154  0.729  1.0
  O  O19  1  0.077  0.852  0.776  1.0
  O  O20  1  0.727  0.479  0.752  1.0
  O  O21  1  0.748  0.000  0.748  1.0
  O  O22  1  0.411  0.635  0.776  1.0
  O  O23  1  0.141  0.365  0.776  1.0
  O  O24  1  0.424  0.695  0.271  1.0
  O  O25  1  0.077  0.301  0.224  1.0
  O  O26  1  0.727  0.975  0.248  1.0
  O  O27  1  0.576  0.846  0.271  1.0
  O  O28  1  0.273  0.521  0.248  1.0
  O  O29  1  0.923  0.148  0.224  1.0
[/CIF]
.