The structure described by Sr4Nb2O9 crystallizes in the triclinic P-1 space group. There are five inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 6-coordinate geometry to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. In the third Sr site, Sr(3) is bonded to two equivalent O(7), two equivalent O(8), and two equivalent O(9) atoms to form SrO6 octahedra that share corners with six equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-40°. In the fourth Sr site, Sr(4) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form SrO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra and corners with six equivalent Sr(5)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 33-35°. In the fifth Sr site, Sr(5) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted SrO6 pentagonal pyramids that share corners with three equivalent Sr(4)O6 octahedra, corners with three equivalent Nb(2)O6 octahedra, and edges with three equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 20-70°. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted NbO6 octahedra that share corners with three equivalent Sr(4)O6 octahedra, edges with three equivalent Sr(5)O6 pentagonal pyramids, and  a faceface with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 33-35°. In the second Nb site, Nb(2) is bonded to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form distorted NbO6 octahedra that share corners with three equivalent Sr(3)O6 octahedra, corners with three equivalent Sr(5)O6 pentagonal pyramids, and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-40°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sr(2), one Sr(4), one Sr(5), and one Nb(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sr(2), one Sr(4), one Sr(5), and one Nb(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Sr(2), one Sr(4), one Sr(5), and one Nb(1) atom. In the fourth O site, O(4) is bonded to one Sr(1), one Sr(2), one Sr(5), one Nb(1), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb2 trigonal bipyramids. In the fifth O site, O(5) is bonded to one Sr(1), one Sr(2), one Sr(5), one Nb(1), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb2 square pyramids. In the sixth O site, O(6) is bonded to one Sr(1), one Sr(2), one Sr(5), one Nb(1), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb2 square pyramids. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Sr(1), one Sr(2), one Sr(3), and one Nb(2) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Sr(3), and one Nb(2) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Sr(1), one Sr(3), and one Nb(2) atom. is represented by the CIF file [CIF]
data_Sr4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.933
_cell_length_b   5.960
_cell_length_c   15.812
_cell_angle_alpha   89.998
_cell_angle_beta   90.022
_cell_angle_gamma   119.796
_symmetry_Int_Tables_number   1
_cell_volume   485.215
_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  0.337  0.641  0.133  1.0
  Sr  Sr1  1  0.663  0.359  0.867  1.0
  Sr  Sr2  1  0.004  0.991  0.252  1.0
  Sr  Sr3  1  0.996  0.009  0.748  1.0
  Sr  Sr4  1  0.000  0.000  0.000  1.0
  Sr  Sr5  1  0.000  0.000  0.500  1.0
  Sr  Sr6  1  0.666  0.340  0.643  1.0
  Sr  Sr7  1  0.334  0.660  0.357  1.0
  Nb  Nb8  1  0.669  0.324  0.344  1.0
  Nb  Nb9  1  0.331  0.676  0.656  1.0
  Nb  Nb10  1  0.337  0.694  0.849  1.0
  Nb  Nb11  1  0.663  0.306  0.151  1.0
  O  O12  1  0.652  0.928  0.605  1.0
  O  O13  1  0.348  0.072  0.395  1.0
  O  O14  1  0.076  0.738  0.605  1.0
  O  O15  1  0.924  0.262  0.395  1.0
  O  O16  1  0.273  0.362  0.603  1.0
  O  O17  1  0.727  0.638  0.397  1.0
  O  O18  1  0.960  0.544  0.248  1.0
  O  O19  1  0.040  0.456  0.752  1.0
  O  O20  1  0.449  0.394  0.244  1.0
  O  O21  1  0.551  0.606  0.756  1.0
  O  O22  1  0.588  0.016  0.250  1.0
  O  O23  1  0.412  0.984  0.750  1.0
  O  O24  1  0.354  0.047  0.098  1.0
  O  O25  1  0.646  0.953  0.902  1.0
  O  O26  1  0.926  0.232  0.112  1.0
  O  O27  1  0.074  0.768  0.888  1.0
  O  O28  1  0.722  0.599  0.086  1.0
  O  O29  1  0.278  0.401  0.914  1.0
[/CIF]
.
The structure described by Sr4Nb2O9 crystallizes in the triclinic P-1 space group. There are five inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 6-coordinate geometry to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. In the third Sr site, Sr(3) is bonded to two equivalent O(7), two equivalent O(8), and two equivalent O(9) atoms to form SrO6 octahedra that share corners with six equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-40°. In the fourth Sr site, Sr(4) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form SrO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra and corners with six equivalent Sr(5)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 33-35°. In the fifth Sr site, Sr(5) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted SrO6 pentagonal pyramids that share corners with three equivalent Sr(4)O6 octahedra, corners with three equivalent Nb(2)O6 octahedra, and edges with three equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 20-70°. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted NbO6 octahedra that share corners with three equivalent Sr(4)O6 octahedra, edges with three equivalent Sr(5)O6 pentagonal pyramids, and  a faceface with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 33-35°. In the second Nb site, Nb(2) is bonded to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form distorted NbO6 octahedra that share corners with three equivalent Sr(3)O6 octahedra, corners with three equivalent Sr(5)O6 pentagonal pyramids, and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-40°. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Sr(2), one Sr(4), one Sr(5), and one Nb(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Sr(2), one Sr(4), one Sr(5), and one Nb(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Sr(2), one Sr(4), one Sr(5), and one Nb(1) atom. In the fourth O site, O(4) is bonded to one Sr(1), one Sr(2), one Sr(5), one Nb(1), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb2 trigonal bipyramids. In the fifth O site, O(5) is bonded to one Sr(1), one Sr(2), one Sr(5), one Nb(1), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb2 square pyramids. In the sixth O site, O(6) is bonded to one Sr(1), one Sr(2), one Sr(5), one Nb(1), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb2 square pyramids. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Sr(1), one Sr(2), one Sr(3), and one Nb(2) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Sr(1), one Sr(2), one Sr(3), and one Nb(2) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Sr(1), one Sr(3), and one Nb(2) atom. is represented by the CIF file [CIF]
data_Sr4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.933
_cell_length_b   5.960
_cell_length_c   15.812
_cell_angle_alpha   89.998
_cell_angle_beta   90.022
_cell_angle_gamma   119.796
_symmetry_Int_Tables_number   1
_cell_volume   485.215
_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  0.337  0.641  0.133  1.0
  Sr  Sr1  1  0.663  0.359  0.867  1.0
  Sr  Sr2  1  0.004  0.991  0.252  1.0
  Sr  Sr3  1  0.996  0.009  0.748  1.0
  Sr  Sr4  1  0.000  0.000  0.000  1.0
  Sr  Sr5  1  0.000  0.000  0.500  1.0
  Sr  Sr6  1  0.666  0.340  0.643  1.0
  Sr  Sr7  1  0.334  0.660  0.357  1.0
  Nb  Nb8  1  0.669  0.324  0.344  1.0
  Nb  Nb9  1  0.331  0.676  0.656  1.0
  Nb  Nb10  1  0.337  0.694  0.849  1.0
  Nb  Nb11  1  0.663  0.306  0.151  1.0
  O  O12  1  0.652  0.928  0.605  1.0
  O  O13  1  0.348  0.072  0.395  1.0
  O  O14  1  0.076  0.738  0.605  1.0
  O  O15  1  0.924  0.262  0.395  1.0
  O  O16  1  0.273  0.362  0.603  1.0
  O  O17  1  0.727  0.638  0.397  1.0
  O  O18  1  0.960  0.544  0.248  1.0
  O  O19  1  0.040  0.456  0.752  1.0
  O  O20  1  0.449  0.394  0.244  1.0
  O  O21  1  0.551  0.606  0.756  1.0
  O  O22  1  0.588  0.016  0.250  1.0
  O  O23  1  0.412  0.984  0.750  1.0
  O  O24  1  0.354  0.047  0.098  1.0
  O  O25  1  0.646  0.953  0.902  1.0
  O  O26  1  0.926  0.232  0.112  1.0
  O  O27  1  0.074  0.768  0.888  1.0
  O  O28  1  0.722  0.599  0.086  1.0
  O  O29  1  0.278  0.401  0.914  1.0
[/CIF]
.