The structure described by Er3TaO7 crystallizes in the triclinic P-1 space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(3), one O(4), one O(7), two equivalent O(2), and two equivalent O(6) atoms to form distorted ErO7 pentagonal bipyramids that share  a cornercorner with one Ta(1)O6 octahedra,  a cornercorner with one Ta(2)O6 octahedra,  a cornercorner with one Er(3)O7 pentagonal bipyramid,  an edgeedge with one Ta(1)O6 octahedra, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with two equivalent Er(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 46-50°. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(5), one O(6), two equivalent O(4), and two equivalent O(7) atoms. In the third Er site, Er(3) is bonded to one O(5), one O(6), one O(7), two equivalent O(1), and two equivalent O(3) atoms to form distorted ErO7 pentagonal bipyramids that share  a cornercorner with one Ta(1)O6 octahedra,  a cornercorner with one Ta(2)O6 octahedra,  a cornercorner with one Er(1)O7 pentagonal bipyramid,  an edgeedge with one Ta(1)O6 octahedra,  an edgeedge with one Ta(2)O6 octahedra, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with two equivalent Er(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 44-45°. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms to form TaO6 octahedra that share corners with two equivalent Ta(2)O6 octahedra, corners with two equivalent Er(1)O7 pentagonal bipyramids, corners with two equivalent Er(3)O7 pentagonal bipyramids, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with two equivalent Er(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. In the second Ta site, Ta(2) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Er(1)O7 pentagonal bipyramids, corners with two equivalent Er(3)O7 pentagonal bipyramids, and edges with two equivalent Er(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Er(2), two equivalent Er(3), and one Ta(2) atom to form distorted OEr3Ta trigonal pyramids that share  a cornercorner with one O(6)Er4 tetrahedra, corners with two equivalent O(4)Er3Ta tetrahedra, corners with two equivalent O(7)Er4 tetrahedra, corners with four equivalent O(3)Er3Ta tetrahedra,  a cornercorner with one O(1)Er3Ta trigonal pyramid,  an edgeedge with one O(4)Er3Ta tetrahedra,  an edgeedge with one O(6)Er4 tetrahedra,  an edgeedge with one O(7)Er4 tetrahedra, and  an edgeedge with one O(1)Er3Ta trigonal pyramid. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Er(2), two equivalent Er(1), and one Ta(1) atom. In the third O site, O(3) is bonded to one Er(1), two equivalent Er(3), and one Ta(1) atom to form distorted OEr3Ta tetrahedra that share  a cornercorner with one O(3)Er3Ta tetrahedra,  a cornercorner with one O(4)Er3Ta tetrahedra,  a cornercorner with one O(7)Er4 tetrahedra, corners with two equivalent O(6)Er4 tetrahedra, corners with four equivalent O(1)Er3Ta trigonal pyramids,  an edgeedge with one O(3)Er3Ta tetrahedra,  an edgeedge with one O(6)Er4 tetrahedra, and  an edgeedge with one O(7)Er4 tetrahedra. In the fourth O site, O(4) is bonded to one Er(1), two equivalent Er(2), and one Ta(2) atom to form distorted OEr3Ta tetrahedra that share  a cornercorner with one O(3)Er3Ta tetrahedra,  a cornercorner with one O(4)Er3Ta tetrahedra, corners with three equivalent O(7)Er4 tetrahedra, corners with four equivalent O(6)Er4 tetrahedra, corners with two equivalent O(1)Er3Ta trigonal pyramids,  an edgeedge with one O(4)Er3Ta tetrahedra,  an edgeedge with one O(7)Er4 tetrahedra, and  an edgeedge with one O(1)Er3Ta trigonal pyramid. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Er(2), one Er(3), one Ta(1), and one Ta(2) atom. In the sixth O site, O(6) is bonded to one Er(2), one Er(3), and two equivalent Er(1) atoms to form OEr4 tetrahedra that share corners with two equivalent O(3)Er3Ta tetrahedra, corners with three equivalent O(7)Er4 tetrahedra, corners with four equivalent O(4)Er3Ta tetrahedra,  a cornercorner with one O(1)Er3Ta trigonal pyramid,  an edgeedge with one O(3)Er3Ta tetrahedra,  an edgeedge with one O(6)Er4 tetrahedra,  an edgeedge with one O(7)Er4 tetrahedra, and  an edgeedge with one O(1)Er3Ta trigonal pyramid. In the seventh O site, O(7) is bonded to one Er(1), one Er(3), and two equivalent Er(2) atoms to form OEr4 tetrahedra that share  a cornercorner with one O(3)Er3Ta tetrahedra, corners with three equivalent O(4)Er3Ta tetrahedra, corners with three equivalent O(6)Er4 tetrahedra, corners with two equivalent O(1)Er3Ta trigonal pyramids,  an edgeedge with one O(3)Er3Ta tetrahedra,  an edgeedge with one O(4)Er3Ta tetrahedra,  an edgeedge with one O(6)Er4 tetrahedra,  an edgeedge with one O(7)Er4 tetrahedra, and  an edgeedge with one O(1)Er3Ta trigonal pyramid. is represented by the CIF file [CIF]
data_Er3TaO7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.272
_cell_length_b   6.384
_cell_length_c   7.474
_cell_angle_alpha   106.804
_cell_angle_beta   89.712
_cell_angle_gamma   97.739
_symmetry_Int_Tables_number   1
_cell_volume   283.642
_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
  Er  Er0  1  0.736  0.462  0.116  1.0
  Er  Er1  1  0.733  0.456  0.608  1.0
  Er  Er2  1  0.545  0.993  0.750  1.0
  Er  Er3  1  0.455  0.007  0.250  1.0
  Er  Er4  1  0.267  0.544  0.392  1.0
  Er  Er5  1  0.264  0.538  0.884  1.0
  Ta  Ta6  1  0.000  0.000  0.000  1.0
  Ta  Ta7  1  0.000  0.000  0.500  1.0
  O  O8  1  0.707  0.069  0.481  1.0
  O  O9  1  0.920  0.676  0.952  1.0
  O  O10  1  0.706  0.074  0.052  1.0
  O  O11  1  0.926  0.666  0.390  1.0
  O  O12  1  0.906  0.950  0.737  1.0
  O  O13  1  0.556  0.347  0.834  1.0
  O  O14  1  0.539  0.361  0.341  1.0
  O  O15  1  0.461  0.639  0.659  1.0
  O  O16  1  0.444  0.653  0.166  1.0
  O  O17  1  0.094  0.050  0.263  1.0
  O  O18  1  0.074  0.334  0.610  1.0
  O  O19  1  0.294  0.926  0.948  1.0
  O  O20  1  0.080  0.324  0.048  1.0
  O  O21  1  0.293  0.931  0.519  1.0
[/CIF]
.
The structure described by Er3TaO7 crystallizes in the triclinic P-1 space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(3), one O(4), one O(7), two equivalent O(2), and two equivalent O(6) atoms to form distorted ErO7 pentagonal bipyramids that share  a cornercorner with one Ta(1)O6 octahedra,  a cornercorner with one Ta(2)O6 octahedra,  a cornercorner with one Er(3)O7 pentagonal bipyramid,  an edgeedge with one Ta(1)O6 octahedra, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with two equivalent Er(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 46-50°. In the second Er site, Er(2) is bonded in a 8-coordinate geometry to one O(1), one O(2), one O(5), one O(6), two equivalent O(4), and two equivalent O(7) atoms. In the third Er site, Er(3) is bonded to one O(5), one O(6), one O(7), two equivalent O(1), and two equivalent O(3) atoms to form distorted ErO7 pentagonal bipyramids that share  a cornercorner with one Ta(1)O6 octahedra,  a cornercorner with one Ta(2)O6 octahedra,  a cornercorner with one Er(1)O7 pentagonal bipyramid,  an edgeedge with one Ta(1)O6 octahedra,  an edgeedge with one Ta(2)O6 octahedra, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with two equivalent Er(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 44-45°. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(5) atoms to form TaO6 octahedra that share corners with two equivalent Ta(2)O6 octahedra, corners with two equivalent Er(1)O7 pentagonal bipyramids, corners with two equivalent Er(3)O7 pentagonal bipyramids, edges with two equivalent Er(1)O7 pentagonal bipyramids, and edges with two equivalent Er(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. In the second Ta site, Ta(2) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(5) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Er(1)O7 pentagonal bipyramids, corners with two equivalent Er(3)O7 pentagonal bipyramids, and edges with two equivalent Er(3)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. There are seven inequivalent O sites. In the first O site, O(1) is bonded to one Er(2), two equivalent Er(3), and one Ta(2) atom to form distorted OEr3Ta trigonal pyramids that share  a cornercorner with one O(6)Er4 tetrahedra, corners with two equivalent O(4)Er3Ta tetrahedra, corners with two equivalent O(7)Er4 tetrahedra, corners with four equivalent O(3)Er3Ta tetrahedra,  a cornercorner with one O(1)Er3Ta trigonal pyramid,  an edgeedge with one O(4)Er3Ta tetrahedra,  an edgeedge with one O(6)Er4 tetrahedra,  an edgeedge with one O(7)Er4 tetrahedra, and  an edgeedge with one O(1)Er3Ta trigonal pyramid. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Er(2), two equivalent Er(1), and one Ta(1) atom. In the third O site, O(3) is bonded to one Er(1), two equivalent Er(3), and one Ta(1) atom to form distorted OEr3Ta tetrahedra that share  a cornercorner with one O(3)Er3Ta tetrahedra,  a cornercorner with one O(4)Er3Ta tetrahedra,  a cornercorner with one O(7)Er4 tetrahedra, corners with two equivalent O(6)Er4 tetrahedra, corners with four equivalent O(1)Er3Ta trigonal pyramids,  an edgeedge with one O(3)Er3Ta tetrahedra,  an edgeedge with one O(6)Er4 tetrahedra, and  an edgeedge with one O(7)Er4 tetrahedra. In the fourth O site, O(4) is bonded to one Er(1), two equivalent Er(2), and one Ta(2) atom to form distorted OEr3Ta tetrahedra that share  a cornercorner with one O(3)Er3Ta tetrahedra,  a cornercorner with one O(4)Er3Ta tetrahedra, corners with three equivalent O(7)Er4 tetrahedra, corners with four equivalent O(6)Er4 tetrahedra, corners with two equivalent O(1)Er3Ta trigonal pyramids,  an edgeedge with one O(4)Er3Ta tetrahedra,  an edgeedge with one O(7)Er4 tetrahedra, and  an edgeedge with one O(1)Er3Ta trigonal pyramid. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Er(2), one Er(3), one Ta(1), and one Ta(2) atom. In the sixth O site, O(6) is bonded to one Er(2), one Er(3), and two equivalent Er(1) atoms to form OEr4 tetrahedra that share corners with two equivalent O(3)Er3Ta tetrahedra, corners with three equivalent O(7)Er4 tetrahedra, corners with four equivalent O(4)Er3Ta tetrahedra,  a cornercorner with one O(1)Er3Ta trigonal pyramid,  an edgeedge with one O(3)Er3Ta tetrahedra,  an edgeedge with one O(6)Er4 tetrahedra,  an edgeedge with one O(7)Er4 tetrahedra, and  an edgeedge with one O(1)Er3Ta trigonal pyramid. In the seventh O site, O(7) is bonded to one Er(1), one Er(3), and two equivalent Er(2) atoms to form OEr4 tetrahedra that share  a cornercorner with one O(3)Er3Ta tetrahedra, corners with three equivalent O(4)Er3Ta tetrahedra, corners with three equivalent O(6)Er4 tetrahedra, corners with two equivalent O(1)Er3Ta trigonal pyramids,  an edgeedge with one O(3)Er3Ta tetrahedra,  an edgeedge with one O(4)Er3Ta tetrahedra,  an edgeedge with one O(6)Er4 tetrahedra,  an edgeedge with one O(7)Er4 tetrahedra, and  an edgeedge with one O(1)Er3Ta trigonal pyramid. is represented by the CIF file [CIF]
data_Er3TaO7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.272
_cell_length_b   6.384
_cell_length_c   7.474
_cell_angle_alpha   106.804
_cell_angle_beta   89.712
_cell_angle_gamma   97.739
_symmetry_Int_Tables_number   1
_cell_volume   283.642
_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
  Er  Er0  1  0.736  0.462  0.116  1.0
  Er  Er1  1  0.733  0.456  0.608  1.0
  Er  Er2  1  0.545  0.993  0.750  1.0
  Er  Er3  1  0.455  0.007  0.250  1.0
  Er  Er4  1  0.267  0.544  0.392  1.0
  Er  Er5  1  0.264  0.538  0.884  1.0
  Ta  Ta6  1  0.000  0.000  0.000  1.0
  Ta  Ta7  1  0.000  0.000  0.500  1.0
  O  O8  1  0.707  0.069  0.481  1.0
  O  O9  1  0.920  0.676  0.952  1.0
  O  O10  1  0.706  0.074  0.052  1.0
  O  O11  1  0.926  0.666  0.390  1.0
  O  O12  1  0.906  0.950  0.737  1.0
  O  O13  1  0.556  0.347  0.834  1.0
  O  O14  1  0.539  0.361  0.341  1.0
  O  O15  1  0.461  0.639  0.659  1.0
  O  O16  1  0.444  0.653  0.166  1.0
  O  O17  1  0.094  0.050  0.263  1.0
  O  O18  1  0.074  0.334  0.610  1.0
  O  O19  1  0.294  0.926  0.948  1.0
  O  O20  1  0.080  0.324  0.048  1.0
  O  O21  1  0.293  0.931  0.519  1.0
[/CIF]
.