The crystal structure described by Sr6Ta2O11 crystallizes in the tetragonal P4/nmm space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 9-coordinate geometry to one O(4), two equivalent O(2), two equivalent O(3), and four equivalent O(1) atoms. In the second Sr site, Sr(2) is bonded to one O(4) and four equivalent O(1) atoms to form distorted SrO5 square pyramids that share corners with four equivalent Ta(2)O6 octahedra and  a cornercorner with one Ta(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 10°. In the third Sr site, Sr(3) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(3) atoms. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(4) and four equivalent O(3) atoms to form distorted TaO5 trigonal bipyramids that share  a cornercorner with one Sr(2)O5 square pyramid. In the second Ta site, Ta(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form TaO6 octahedra that share corners with four equivalent Sr(2)O5 square pyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Sr(2), four equivalent Sr(1), and one Ta(2) atom to form distorted OSr5Ta octahedra that share corners with two equivalent O(1)Sr5Ta octahedra, corners with six equivalent O(3)Sr3Ta tetrahedra, edges with two equivalent O(1)Sr5Ta octahedra,  an edgeedge with one O(3)Sr3Ta tetrahedra, and faces with four equivalent O(1)Sr5Ta octahedra. The corner-sharing octahedral tilt angles range from 4-16°. In the second O site, O(2) is bonded in a distorted linear geometry to one Sr(3), four equivalent Sr(1), and one Ta(2) atom. In the third O site, O(3) is bonded to one Sr(3), two equivalent Sr(1), and one Ta(1) atom to form distorted OSr3Ta tetrahedra that share corners with six equivalent O(1)Sr5Ta octahedra, corners with four equivalent O(3)Sr3Ta tetrahedra,  an edgeedge with one O(1)Sr5Ta octahedra, and edges with two equivalent O(3)Sr3Ta tetrahedra. The corner-sharing octahedral tilt angles range from 11-70°. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Sr(2), four equivalent Sr(1), and one Ta(1) atom. is represented by the CIF file [CIF]
data_Sr6Ta2O11
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.567
_cell_length_b   8.567
_cell_length_c   8.546
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   627.300
_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  0.751  0.251  0.723  1.0
  Sr  Sr1  1  0.500  0.000  0.530  1.0
  Sr  Sr2  1  0.500  0.500  0.000  1.0
  Sr  Sr3  1  0.749  0.751  0.277  1.0
  Sr  Sr4  1  0.000  0.500  0.470  1.0
  Sr  Sr5  1  0.249  0.749  0.723  1.0
  Sr  Sr6  1  0.251  0.751  0.277  1.0
  Sr  Sr7  1  0.000  0.000  0.000  1.0
  Sr  Sr8  1  0.249  0.251  0.723  1.0
  Sr  Sr9  1  0.251  0.249  0.277  1.0
  Sr  Sr10  1  0.749  0.249  0.277  1.0
  Sr  Sr11  1  0.751  0.749  0.723  1.0
  Ta  Ta12  1  0.000  0.500  0.027  1.0
  Ta  Ta13  1  0.000  0.000  0.500  1.0
  Ta  Ta14  1  0.500  0.000  0.973  1.0
  Ta  Ta15  1  0.500  0.500  0.500  1.0
  O  O16  1  0.765  0.000  0.492  1.0
  O  O17  1  0.500  0.265  0.492  1.0
  O  O18  1  0.500  0.500  0.728  1.0
  O  O19  1  0.265  0.500  0.508  1.0
  O  O20  1  0.500  0.782  0.899  1.0
  O  O21  1  0.000  0.500  0.804  1.0
  O  O22  1  0.500  0.000  0.196  1.0
  O  O23  1  0.000  0.718  0.101  1.0
  O  O24  1  0.282  0.000  0.899  1.0
  O  O25  1  0.000  0.765  0.508  1.0
  O  O26  1  0.235  0.000  0.492  1.0
  O  O27  1  0.000  0.000  0.272  1.0
  O  O28  1  0.000  0.000  0.728  1.0
  O  O29  1  0.000  0.235  0.508  1.0
  O  O30  1  0.000  0.282  0.101  1.0
  O  O31  1  0.718  0.000  0.899  1.0
  O  O32  1  0.500  0.218  0.899  1.0
  O  O33  1  0.782  0.500  0.101  1.0
  O  O34  1  0.735  0.500  0.508  1.0
  O  O35  1  0.500  0.500  0.272  1.0
  O  O36  1  0.500  0.735  0.492  1.0
  O  O37  1  0.218  0.500  0.101  1.0
[/CIF]
.
The crystal structure described by Sr6Ta2O11 crystallizes in the tetragonal P4/nmm space group. There are three inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 9-coordinate geometry to one O(4), two equivalent O(2), two equivalent O(3), and four equivalent O(1) atoms. In the second Sr site, Sr(2) is bonded to one O(4) and four equivalent O(1) atoms to form distorted SrO5 square pyramids that share corners with four equivalent Ta(2)O6 octahedra and  a cornercorner with one Ta(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 10°. In the third Sr site, Sr(3) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(3) atoms. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(4) and four equivalent O(3) atoms to form distorted TaO5 trigonal bipyramids that share  a cornercorner with one Sr(2)O5 square pyramid. In the second Ta site, Ta(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form TaO6 octahedra that share corners with four equivalent Sr(2)O5 square pyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Sr(2), four equivalent Sr(1), and one Ta(2) atom to form distorted OSr5Ta octahedra that share corners with two equivalent O(1)Sr5Ta octahedra, corners with six equivalent O(3)Sr3Ta tetrahedra, edges with two equivalent O(1)Sr5Ta octahedra,  an edgeedge with one O(3)Sr3Ta tetrahedra, and faces with four equivalent O(1)Sr5Ta octahedra. The corner-sharing octahedral tilt angles range from 4-16°. In the second O site, O(2) is bonded in a distorted linear geometry to one Sr(3), four equivalent Sr(1), and one Ta(2) atom. In the third O site, O(3) is bonded to one Sr(3), two equivalent Sr(1), and one Ta(1) atom to form distorted OSr3Ta tetrahedra that share corners with six equivalent O(1)Sr5Ta octahedra, corners with four equivalent O(3)Sr3Ta tetrahedra,  an edgeedge with one O(1)Sr5Ta octahedra, and edges with two equivalent O(3)Sr3Ta tetrahedra. The corner-sharing octahedral tilt angles range from 11-70°. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to one Sr(2), four equivalent Sr(1), and one Ta(1) atom. is represented by the CIF file [CIF]
data_Sr6Ta2O11
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.567
_cell_length_b   8.567
_cell_length_c   8.546
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   627.300
_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  0.751  0.251  0.723  1.0
  Sr  Sr1  1  0.500  0.000  0.530  1.0
  Sr  Sr2  1  0.500  0.500  0.000  1.0
  Sr  Sr3  1  0.749  0.751  0.277  1.0
  Sr  Sr4  1  0.000  0.500  0.470  1.0
  Sr  Sr5  1  0.249  0.749  0.723  1.0
  Sr  Sr6  1  0.251  0.751  0.277  1.0
  Sr  Sr7  1  0.000  0.000  0.000  1.0
  Sr  Sr8  1  0.249  0.251  0.723  1.0
  Sr  Sr9  1  0.251  0.249  0.277  1.0
  Sr  Sr10  1  0.749  0.249  0.277  1.0
  Sr  Sr11  1  0.751  0.749  0.723  1.0
  Ta  Ta12  1  0.000  0.500  0.027  1.0
  Ta  Ta13  1  0.000  0.000  0.500  1.0
  Ta  Ta14  1  0.500  0.000  0.973  1.0
  Ta  Ta15  1  0.500  0.500  0.500  1.0
  O  O16  1  0.765  0.000  0.492  1.0
  O  O17  1  0.500  0.265  0.492  1.0
  O  O18  1  0.500  0.500  0.728  1.0
  O  O19  1  0.265  0.500  0.508  1.0
  O  O20  1  0.500  0.782  0.899  1.0
  O  O21  1  0.000  0.500  0.804  1.0
  O  O22  1  0.500  0.000  0.196  1.0
  O  O23  1  0.000  0.718  0.101  1.0
  O  O24  1  0.282  0.000  0.899  1.0
  O  O25  1  0.000  0.765  0.508  1.0
  O  O26  1  0.235  0.000  0.492  1.0
  O  O27  1  0.000  0.000  0.272  1.0
  O  O28  1  0.000  0.000  0.728  1.0
  O  O29  1  0.000  0.235  0.508  1.0
  O  O30  1  0.000  0.282  0.101  1.0
  O  O31  1  0.718  0.000  0.899  1.0
  O  O32  1  0.500  0.218  0.899  1.0
  O  O33  1  0.782  0.500  0.101  1.0
  O  O34  1  0.735  0.500  0.508  1.0
  O  O35  1  0.500  0.500  0.272  1.0
  O  O36  1  0.500  0.735  0.492  1.0
  O  O37  1  0.218  0.500  0.101  1.0
[/CIF]
.