The crystal structure described by Ta3(Bi2O7)2 crystallizes in the monoclinic C2/c space group. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(2), one O(4), one O(5), one O(7), and two equivalent O(1) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, corners with two equivalent Bi(1)O7 pentagonal bipyramids, and  an edgeedge with one Bi(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 34-36°. In the second Ta site, Ta(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(7) atoms to form TaO6 octahedra that share corners with four equivalent Ta(1)O6 octahedra, corners with two equivalent Bi(1)O7 pentagonal bipyramids, and edges with two equivalent Bi(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 34-36°. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(5), one O(6), one O(7), two equivalent O(3), and two equivalent O(4) atoms to form distorted BiO7 pentagonal bipyramids that share  a cornercorner with one Ta(2)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra,  an edgeedge with one Ta(1)O6 octahedra,  an edgeedge with one Ta(2)O6 octahedra, and edges with two equivalent Bi(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 43-44°. In the second Bi site, Bi(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), two equivalent O(5), and two equivalent O(6) atoms. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a bent 150 degrees geometry to one Ta(1), one Ta(2), and one Bi(2) atom. In the second O site, O(3) is bonded to one Ta(2), one Bi(2), and two equivalent Bi(1) atoms to form a mixture of distorted edge and corner-sharing OTaBi3 tetrahedra. In the third O site, O(4) is bonded to one Ta(1), one Bi(2), and two equivalent Bi(1) atoms to form a mixture of distorted edge and corner-sharing OTaBi3 tetrahedra. In the fourth O site, O(5) is bonded in a 2-coordinate geometry to one Ta(1), one Bi(1), and two equivalent Bi(2) atoms. In the fifth O site, O(6) is bonded in a trigonal non-coplanar geometry to one Bi(1) and two equivalent Bi(2) atoms. In the sixth O site, O(7) is bonded in a 3-coordinate geometry to one Ta(1), one Ta(2), and one Bi(1) atom. In the seventh O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ta(1) and one Bi(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ta3(Bi2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.653
_cell_length_b   7.653
_cell_length_c   12.086
_cell_angle_alpha   79.962
_cell_angle_beta   79.962
_cell_angle_gamma   60.022
_symmetry_Int_Tables_number   1
_cell_volume   600.641
_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
  Ta  Ta0  1  0.139  0.358  0.759  1.0
  Ta  Ta1  1  0.642  0.861  0.741  1.0
  Ta  Ta2  1  0.861  0.642  0.241  1.0
  Ta  Ta3  1  0.358  0.139  0.259  1.0
  Ta  Ta4  1  0.151  0.849  0.750  1.0
  Ta  Ta5  1  0.849  0.151  0.250  1.0
  Bi  Bi6  1  0.027  0.744  0.469  1.0
  Bi  Bi7  1  0.256  0.973  0.031  1.0
  Bi  Bi8  1  0.973  0.256  0.531  1.0
  Bi  Bi9  1  0.744  0.027  0.969  1.0
  Bi  Bi10  1  0.492  0.272  0.507  1.0
  Bi  Bi11  1  0.728  0.508  0.993  1.0
  Bi  Bi12  1  0.508  0.728  0.493  1.0
  Bi  Bi13  1  0.272  0.492  0.007  1.0
  O  O14  1  0.847  0.565  0.783  1.0
  O  O15  1  0.435  0.153  0.717  1.0
  O  O16  1  0.153  0.435  0.217  1.0
  O  O17  1  0.565  0.847  0.283  1.0
  O  O18  1  0.212  0.566  0.781  1.0
  O  O19  1  0.434  0.788  0.719  1.0
  O  O20  1  0.788  0.434  0.219  1.0
  O  O21  1  0.566  0.212  0.281  1.0
  O  O22  1  0.130  0.862  0.916  1.0
  O  O23  1  0.138  0.870  0.584  1.0
  O  O24  1  0.870  0.138  0.084  1.0
  O  O25  1  0.862  0.130  0.416  1.0
  O  O26  1  0.143  0.445  0.586  1.0
  O  O27  1  0.555  0.857  0.914  1.0
  O  O28  1  0.857  0.555  0.414  1.0
  O  O29  1  0.445  0.143  0.086  1.0
  O  O30  1  0.147  0.272  0.918  1.0
  O  O31  1  0.728  0.853  0.582  1.0
  O  O32  1  0.853  0.728  0.082  1.0
  O  O33  1  0.272  0.147  0.418  1.0
  O  O34  1  0.631  0.415  0.580  1.0
  O  O35  1  0.585  0.369  0.920  1.0
  O  O36  1  0.369  0.585  0.420  1.0
  O  O37  1  0.415  0.631  0.080  1.0
  O  O38  1  0.068  0.153  0.728  1.0
  O  O39  1  0.847  0.932  0.772  1.0
  O  O40  1  0.932  0.847  0.272  1.0
  O  O41  1  0.153  0.068  0.228  1.0
[/CIF]
.
The crystal structure described by Ta3(Bi2O7)2 crystallizes in the monoclinic C2/c space group. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(2), one O(4), one O(5), one O(7), and two equivalent O(1) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, corners with two equivalent Bi(1)O7 pentagonal bipyramids, and  an edgeedge with one Bi(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 34-36°. In the second Ta site, Ta(2) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(7) atoms to form TaO6 octahedra that share corners with four equivalent Ta(1)O6 octahedra, corners with two equivalent Bi(1)O7 pentagonal bipyramids, and edges with two equivalent Bi(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 34-36°. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(5), one O(6), one O(7), two equivalent O(3), and two equivalent O(4) atoms to form distorted BiO7 pentagonal bipyramids that share  a cornercorner with one Ta(2)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra,  an edgeedge with one Ta(1)O6 octahedra,  an edgeedge with one Ta(2)O6 octahedra, and edges with two equivalent Bi(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 43-44°. In the second Bi site, Bi(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(3), one O(4), two equivalent O(5), and two equivalent O(6) atoms. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a bent 150 degrees geometry to one Ta(1), one Ta(2), and one Bi(2) atom. In the second O site, O(3) is bonded to one Ta(2), one Bi(2), and two equivalent Bi(1) atoms to form a mixture of distorted edge and corner-sharing OTaBi3 tetrahedra. In the third O site, O(4) is bonded to one Ta(1), one Bi(2), and two equivalent Bi(1) atoms to form a mixture of distorted edge and corner-sharing OTaBi3 tetrahedra. In the fourth O site, O(5) is bonded in a 2-coordinate geometry to one Ta(1), one Bi(1), and two equivalent Bi(2) atoms. In the fifth O site, O(6) is bonded in a trigonal non-coplanar geometry to one Bi(1) and two equivalent Bi(2) atoms. In the sixth O site, O(7) is bonded in a 3-coordinate geometry to one Ta(1), one Ta(2), and one Bi(1) atom. In the seventh O site, O(1) is bonded in a 3-coordinate geometry to two equivalent Ta(1) and one Bi(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_Ta3(Bi2O7)2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.653
_cell_length_b   7.653
_cell_length_c   12.086
_cell_angle_alpha   79.962
_cell_angle_beta   79.962
_cell_angle_gamma   60.022
_symmetry_Int_Tables_number   1
_cell_volume   600.641
_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
  Ta  Ta0  1  0.139  0.358  0.759  1.0
  Ta  Ta1  1  0.642  0.861  0.741  1.0
  Ta  Ta2  1  0.861  0.642  0.241  1.0
  Ta  Ta3  1  0.358  0.139  0.259  1.0
  Ta  Ta4  1  0.151  0.849  0.750  1.0
  Ta  Ta5  1  0.849  0.151  0.250  1.0
  Bi  Bi6  1  0.027  0.744  0.469  1.0
  Bi  Bi7  1  0.256  0.973  0.031  1.0
  Bi  Bi8  1  0.973  0.256  0.531  1.0
  Bi  Bi9  1  0.744  0.027  0.969  1.0
  Bi  Bi10  1  0.492  0.272  0.507  1.0
  Bi  Bi11  1  0.728  0.508  0.993  1.0
  Bi  Bi12  1  0.508  0.728  0.493  1.0
  Bi  Bi13  1  0.272  0.492  0.007  1.0
  O  O14  1  0.847  0.565  0.783  1.0
  O  O15  1  0.435  0.153  0.717  1.0
  O  O16  1  0.153  0.435  0.217  1.0
  O  O17  1  0.565  0.847  0.283  1.0
  O  O18  1  0.212  0.566  0.781  1.0
  O  O19  1  0.434  0.788  0.719  1.0
  O  O20  1  0.788  0.434  0.219  1.0
  O  O21  1  0.566  0.212  0.281  1.0
  O  O22  1  0.130  0.862  0.916  1.0
  O  O23  1  0.138  0.870  0.584  1.0
  O  O24  1  0.870  0.138  0.084  1.0
  O  O25  1  0.862  0.130  0.416  1.0
  O  O26  1  0.143  0.445  0.586  1.0
  O  O27  1  0.555  0.857  0.914  1.0
  O  O28  1  0.857  0.555  0.414  1.0
  O  O29  1  0.445  0.143  0.086  1.0
  O  O30  1  0.147  0.272  0.918  1.0
  O  O31  1  0.728  0.853  0.582  1.0
  O  O32  1  0.853  0.728  0.082  1.0
  O  O33  1  0.272  0.147  0.418  1.0
  O  O34  1  0.631  0.415  0.580  1.0
  O  O35  1  0.585  0.369  0.920  1.0
  O  O36  1  0.369  0.585  0.420  1.0
  O  O37  1  0.415  0.631  0.080  1.0
  O  O38  1  0.068  0.153  0.728  1.0
  O  O39  1  0.847  0.932  0.772  1.0
  O  O40  1  0.932  0.847  0.272  1.0
  O  O41  1  0.153  0.068  0.228  1.0
[/CIF]
.