The compound described by Tb2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. In the second Tb site, Tb(2) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms. In the third Tb site, Tb(3) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Tb(2), two equivalent Tb(1), and two equivalent Tb(3) atoms to form distorted SeTb5 trigonal bipyramids that share corners with five equivalent Se(2)Tb6 octahedra, corners with four equivalent Se(3)Tb5 square pyramids, corners with four equivalent Se(1)Tb5 trigonal bipyramids, edges with three equivalent Se(2)Tb6 octahedra, edges with four equivalent Se(3)Tb5 square pyramids,  an edgeedge with one Se(1)Tb5 trigonal bipyramid,  a faceface with one Se(2)Tb6 octahedra, and  a faceface with one Se(1)Tb5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 25-50°. In the second Se site, Se(2) is bonded to one Tb(3), two equivalent Tb(2), and three equivalent Tb(1) atoms to form distorted SeTb6 octahedra that share corners with three equivalent Se(2)Tb6 octahedra, corners with seven equivalent Se(3)Tb5 square pyramids, corners with five equivalent Se(1)Tb5 trigonal bipyramids, edges with two equivalent Se(2)Tb6 octahedra,  an edgeedge with one Se(3)Tb5 square pyramid, edges with three equivalent Se(1)Tb5 trigonal bipyramids, faces with two equivalent Se(2)Tb6 octahedra, faces with two equivalent Se(3)Tb5 square pyramids, and  a faceface with one Se(1)Tb5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 20-48°. In the third Se site, Se(3) is bonded to one Tb(2), one Tb(3), and three equivalent Tb(1) atoms to form distorted SeTb5 square pyramids that share corners with seven equivalent Se(2)Tb6 octahedra, corners with five equivalent Se(3)Tb5 square pyramids, corners with four equivalent Se(1)Tb5 trigonal bipyramids,  an edgeedge with one Se(2)Tb6 octahedra, edges with four equivalent Se(1)Tb5 trigonal bipyramids, faces with two equivalent Se(2)Tb6 octahedra, and  a faceface with one Se(3)Tb5 square pyramid. The corner-sharing octahedral tilt angles range from 15-54°. is represented by the Crystallographic Information File (CIF) [CIF]
data_Tb2Se3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   22.620
_cell_length_b   8.709
_cell_length_c   8.709
_cell_angle_alpha   90.000
_cell_angle_beta   54.722
_cell_angle_gamma   54.722
_symmetry_Int_Tables_number   1
_cell_volume   990.005
_cell_formula_units_Z   8
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
  Tb  Tb0  1  0.994  0.122  0.769  1.0
  Tb  Tb1  1  0.086  0.621  0.371  1.0
  Tb  Tb2  1  0.167  0.250  0.633  1.0
  Tb  Tb3  1  0.247  0.879  0.129  1.0
  Tb  Tb4  1  0.339  0.378  0.252  1.0
  Tb  Tb5  1  0.167  0.750  0.867  1.0
  Tb  Tb6  1  0.339  0.105  0.731  1.0
  Tb  Tb7  1  0.494  0.269  0.622  1.0
  Tb  Tb8  1  0.586  0.871  0.121  1.0
  Tb  Tb9  1  0.667  0.367  0.250  1.0
  Tb  Tb10  1  0.494  0.748  0.895  1.0
  Tb  Tb11  1  0.667  0.133  0.750  1.0
  Tb  Tb12  1  0.747  0.629  0.379  1.0
  Tb  Tb13  1  0.839  0.231  0.605  1.0
  Tb  Tb14  1  0.994  0.395  0.248  1.0
  Tb  Tb15  1  0.839  0.752  0.878  1.0
  Se  Se16  1  0.129  0.488  0.991  1.0
  Se  Se17  1  0.048  0.359  0.493  1.0
  Se  Se18  1  0.048  0.998  0.364  1.0
  Se  Se19  1  0.286  0.141  0.136  1.0
  Se  Se20  1  0.286  0.502  0.007  1.0
  Se  Se21  1  0.129  0.626  0.624  1.0
  Se  Se22  1  0.205  0.874  0.509  1.0
  Se  Se23  1  0.451  0.495  0.001  1.0
  Se  Se24  1  0.382  0.355  0.505  1.0
  Se  Se25  1  0.205  0.012  0.876  1.0
  Se  Se26  1  0.629  0.124  0.126  1.0
  Se  Se27  1  0.382  0.999  0.349  1.0
  Se  Se28  1  0.629  0.491  0.988  1.0
  Se  Se29  1  0.451  0.651  0.645  1.0
  Se  Se30  1  0.548  0.864  0.498  1.0
  Se  Se31  1  0.786  0.507  0.002  1.0
  Se  Se32  1  0.705  0.376  0.512  1.0
  Se  Se33  1  0.548  0.993  0.859  1.0
  Se  Se34  1  0.705  0.009  0.374  1.0
  Se  Se35  1  0.951  0.145  0.151  1.0
  Se  Se36  1  0.951  0.501  0.995  1.0
  Se  Se37  1  0.786  0.636  0.641  1.0
  Se  Se38  1  0.882  0.849  0.499  1.0
  Se  Se39  1  0.882  0.005  0.855  1.0
[/CIF]
.
The compound described by Tb2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 8-coordinate geometry to two equivalent Se(1), three equivalent Se(2), and three equivalent Se(3) atoms. In the second Tb site, Tb(2) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms. In the third Tb site, Tb(3) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Tb(2), two equivalent Tb(1), and two equivalent Tb(3) atoms to form distorted SeTb5 trigonal bipyramids that share corners with five equivalent Se(2)Tb6 octahedra, corners with four equivalent Se(3)Tb5 square pyramids, corners with four equivalent Se(1)Tb5 trigonal bipyramids, edges with three equivalent Se(2)Tb6 octahedra, edges with four equivalent Se(3)Tb5 square pyramids,  an edgeedge with one Se(1)Tb5 trigonal bipyramid,  a faceface with one Se(2)Tb6 octahedra, and  a faceface with one Se(1)Tb5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 25-50°. In the second Se site, Se(2) is bonded to one Tb(3), two equivalent Tb(2), and three equivalent Tb(1) atoms to form distorted SeTb6 octahedra that share corners with three equivalent Se(2)Tb6 octahedra, corners with seven equivalent Se(3)Tb5 square pyramids, corners with five equivalent Se(1)Tb5 trigonal bipyramids, edges with two equivalent Se(2)Tb6 octahedra,  an edgeedge with one Se(3)Tb5 square pyramid, edges with three equivalent Se(1)Tb5 trigonal bipyramids, faces with two equivalent Se(2)Tb6 octahedra, faces with two equivalent Se(3)Tb5 square pyramids, and  a faceface with one Se(1)Tb5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 20-48°. In the third Se site, Se(3) is bonded to one Tb(2), one Tb(3), and three equivalent Tb(1) atoms to form distorted SeTb5 square pyramids that share corners with seven equivalent Se(2)Tb6 octahedra, corners with five equivalent Se(3)Tb5 square pyramids, corners with four equivalent Se(1)Tb5 trigonal bipyramids,  an edgeedge with one Se(2)Tb6 octahedra, edges with four equivalent Se(1)Tb5 trigonal bipyramids, faces with two equivalent Se(2)Tb6 octahedra, and  a faceface with one Se(3)Tb5 square pyramid. The corner-sharing octahedral tilt angles range from 15-54°. is represented by the Crystallographic Information File (CIF) [CIF]
data_Tb2Se3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   22.620
_cell_length_b   8.709
_cell_length_c   8.709
_cell_angle_alpha   90.000
_cell_angle_beta   54.722
_cell_angle_gamma   54.722
_symmetry_Int_Tables_number   1
_cell_volume   990.005
_cell_formula_units_Z   8
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
  Tb  Tb0  1  0.994  0.122  0.769  1.0
  Tb  Tb1  1  0.086  0.621  0.371  1.0
  Tb  Tb2  1  0.167  0.250  0.633  1.0
  Tb  Tb3  1  0.247  0.879  0.129  1.0
  Tb  Tb4  1  0.339  0.378  0.252  1.0
  Tb  Tb5  1  0.167  0.750  0.867  1.0
  Tb  Tb6  1  0.339  0.105  0.731  1.0
  Tb  Tb7  1  0.494  0.269  0.622  1.0
  Tb  Tb8  1  0.586  0.871  0.121  1.0
  Tb  Tb9  1  0.667  0.367  0.250  1.0
  Tb  Tb10  1  0.494  0.748  0.895  1.0
  Tb  Tb11  1  0.667  0.133  0.750  1.0
  Tb  Tb12  1  0.747  0.629  0.379  1.0
  Tb  Tb13  1  0.839  0.231  0.605  1.0
  Tb  Tb14  1  0.994  0.395  0.248  1.0
  Tb  Tb15  1  0.839  0.752  0.878  1.0
  Se  Se16  1  0.129  0.488  0.991  1.0
  Se  Se17  1  0.048  0.359  0.493  1.0
  Se  Se18  1  0.048  0.998  0.364  1.0
  Se  Se19  1  0.286  0.141  0.136  1.0
  Se  Se20  1  0.286  0.502  0.007  1.0
  Se  Se21  1  0.129  0.626  0.624  1.0
  Se  Se22  1  0.205  0.874  0.509  1.0
  Se  Se23  1  0.451  0.495  0.001  1.0
  Se  Se24  1  0.382  0.355  0.505  1.0
  Se  Se25  1  0.205  0.012  0.876  1.0
  Se  Se26  1  0.629  0.124  0.126  1.0
  Se  Se27  1  0.382  0.999  0.349  1.0
  Se  Se28  1  0.629  0.491  0.988  1.0
  Se  Se29  1  0.451  0.651  0.645  1.0
  Se  Se30  1  0.548  0.864  0.498  1.0
  Se  Se31  1  0.786  0.507  0.002  1.0
  Se  Se32  1  0.705  0.376  0.512  1.0
  Se  Se33  1  0.548  0.993  0.859  1.0
  Se  Se34  1  0.705  0.009  0.374  1.0
  Se  Se35  1  0.951  0.145  0.151  1.0
  Se  Se36  1  0.951  0.501  0.995  1.0
  Se  Se37  1  0.786  0.636  0.641  1.0
  Se  Se38  1  0.882  0.849  0.499  1.0
  Se  Se39  1  0.882  0.005  0.855  1.0
[/CIF]
.