The compound described by Pm2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Pm sites. In the first Pm site, Pm(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), three equivalent Se(1), and three equivalent Se(3) atoms. In the second Pm site, Pm(2) is bonded to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms to form a mixture of distorted face, corner, and edge-sharing PmSe8 hexagonal bipyramids. In the third Pm site, Pm(3) is bonded to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms to form a mixture of distorted face, corner, and edge-sharing PmSe8 hexagonal bipyramids. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Pm(3), two equivalent Pm(2), and three equivalent Pm(1) atoms to form distorted SePm6 octahedra that share corners with three equivalent Se(1)Pm6 octahedra, corners with five equivalent Se(2)Pm5 square pyramids, corners with seven equivalent Se(3)Pm5 square pyramids, edges with two equivalent Se(1)Pm6 octahedra,  an edgeedge with one Se(3)Pm5 square pyramid, edges with three equivalent Se(2)Pm5 square pyramids, faces with two equivalent Se(1)Pm6 octahedra,  a faceface with one Se(2)Pm5 square pyramid, and faces with two equivalent Se(3)Pm5 square pyramids. The corner-sharing octahedral tilt angles range from 18-49°. In the second Se site, Se(2) is bonded to one Pm(2), two equivalent Pm(1), and two equivalent Pm(3) atoms to form distorted SePm5 square pyramids that share corners with five equivalent Se(1)Pm6 octahedra, corners with four equivalent Se(2)Pm5 square pyramids, corners with four equivalent Se(3)Pm5 square pyramids, edges with three equivalent Se(1)Pm6 octahedra,  an edgeedge with one Se(2)Pm5 square pyramid, edges with four equivalent Se(3)Pm5 square pyramids,  a faceface with one Se(1)Pm6 octahedra, and  a faceface with one Se(2)Pm5 square pyramid. The corner-sharing octahedral tilt angles range from 23-49°. In the third Se site, Se(3) is bonded to one Pm(2), one Pm(3), and three equivalent Pm(1) atoms to form distorted SePm5 square pyramids that share corners with seven equivalent Se(1)Pm6 octahedra, corners with four equivalent Se(2)Pm5 square pyramids, corners with five equivalent Se(3)Pm5 square pyramids,  an edgeedge with one Se(1)Pm6 octahedra, edges with four equivalent Se(2)Pm5 square pyramids, faces with two equivalent Se(1)Pm6 octahedra, and  a faceface with one Se(3)Pm5 square pyramid. The corner-sharing octahedral tilt angles range from 14-54°. is represented by the Crystallographic Information File (CIF) [CIF]
data_Pm2Se3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.706
_cell_length_b   14.706
_cell_length_c   14.706
_cell_angle_alpha   144.866
_cell_angle_beta   144.866
_cell_angle_gamma   50.534
_symmetry_Int_Tables_number   1
_cell_volume   1047.973
_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
  Pm  Pm0  1  0.846  0.952  0.377  1.0
  Pm  Pm1  1  0.575  0.469  0.623  1.0
  Pm  Pm2  1  0.166  0.166  0.000  1.0
  Pm  Pm3  1  0.875  0.506  0.131  1.0
  Pm  Pm4  1  0.175  0.298  0.394  1.0
  Pm  Pm5  1  0.584  0.084  0.500  1.0
  Pm  Pm6  1  0.904  0.781  0.606  1.0
  Pm  Pm7  1  0.375  0.744  0.869  1.0
  Pm  Pm8  1  0.219  0.825  0.123  1.0
  Pm  Pm9  1  0.916  0.416  0.500  1.0
  Pm  Pm10  1  0.494  0.625  0.369  1.0
  Pm  Pm11  1  0.256  0.125  0.631  1.0
  Pm  Pm12  1  0.702  0.096  0.877  1.0
  Pm  Pm13  1  0.834  0.834  0.000  1.0
  Pm  Pm14  1  0.531  0.154  0.106  1.0
  Pm  Pm15  1  0.048  0.425  0.894  1.0
  Se  Se16  1  0.507  0.114  0.253  1.0
  Se  Se17  1  0.074  0.827  0.610  1.0
  Se  Se18  1  0.861  0.253  0.747  1.0
  Se  Se19  1  0.889  0.136  0.892  1.0
  Se  Se20  1  0.243  0.997  0.108  1.0
  Se  Se21  1  0.676  0.786  0.253  1.0
  Se  Se22  1  0.217  0.464  0.390  1.0
  Se  Se23  1  0.842  0.437  0.246  1.0
  Se  Se24  1  0.533  0.423  0.747  1.0
  Se  Se25  1  0.404  0.158  0.595  1.0
  Se  Se26  1  0.191  0.596  0.754  1.0
  Se  Se27  1  0.214  0.467  0.890  1.0
  Se  Se28  1  0.577  0.324  0.110  1.0
  Se  Se29  1  0.003  0.111  0.247  1.0
  Se  Se30  1  0.563  0.809  0.405  1.0
  Se  Se31  1  0.173  0.783  0.247  1.0
  Se  Se32  1  0.864  0.757  0.753  1.0
  Se  Se33  1  0.747  0.493  0.608  1.0
  Se  Se34  1  0.536  0.926  0.753  1.0
  Se  Se35  1  0.559  0.813  0.905  1.0
  Se  Se36  1  0.908  0.654  0.095  1.0
  Se  Se37  1  0.346  0.441  0.254  1.0
  Se  Se38  1  0.886  0.139  0.392  1.0
  Se  Se39  1  0.187  0.092  0.746  1.0
[/CIF]
.
The compound described by Pm2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Pm sites. In the first Pm site, Pm(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), three equivalent Se(1), and three equivalent Se(3) atoms. In the second Pm site, Pm(2) is bonded to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms to form a mixture of distorted face, corner, and edge-sharing PmSe8 hexagonal bipyramids. In the third Pm site, Pm(3) is bonded to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms to form a mixture of distorted face, corner, and edge-sharing PmSe8 hexagonal bipyramids. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Pm(3), two equivalent Pm(2), and three equivalent Pm(1) atoms to form distorted SePm6 octahedra that share corners with three equivalent Se(1)Pm6 octahedra, corners with five equivalent Se(2)Pm5 square pyramids, corners with seven equivalent Se(3)Pm5 square pyramids, edges with two equivalent Se(1)Pm6 octahedra,  an edgeedge with one Se(3)Pm5 square pyramid, edges with three equivalent Se(2)Pm5 square pyramids, faces with two equivalent Se(1)Pm6 octahedra,  a faceface with one Se(2)Pm5 square pyramid, and faces with two equivalent Se(3)Pm5 square pyramids. The corner-sharing octahedral tilt angles range from 18-49°. In the second Se site, Se(2) is bonded to one Pm(2), two equivalent Pm(1), and two equivalent Pm(3) atoms to form distorted SePm5 square pyramids that share corners with five equivalent Se(1)Pm6 octahedra, corners with four equivalent Se(2)Pm5 square pyramids, corners with four equivalent Se(3)Pm5 square pyramids, edges with three equivalent Se(1)Pm6 octahedra,  an edgeedge with one Se(2)Pm5 square pyramid, edges with four equivalent Se(3)Pm5 square pyramids,  a faceface with one Se(1)Pm6 octahedra, and  a faceface with one Se(2)Pm5 square pyramid. The corner-sharing octahedral tilt angles range from 23-49°. In the third Se site, Se(3) is bonded to one Pm(2), one Pm(3), and three equivalent Pm(1) atoms to form distorted SePm5 square pyramids that share corners with seven equivalent Se(1)Pm6 octahedra, corners with four equivalent Se(2)Pm5 square pyramids, corners with five equivalent Se(3)Pm5 square pyramids,  an edgeedge with one Se(1)Pm6 octahedra, edges with four equivalent Se(2)Pm5 square pyramids, faces with two equivalent Se(1)Pm6 octahedra, and  a faceface with one Se(3)Pm5 square pyramid. The corner-sharing octahedral tilt angles range from 14-54°. is represented by the Crystallographic Information File (CIF) [CIF]
data_Pm2Se3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.706
_cell_length_b   14.706
_cell_length_c   14.706
_cell_angle_alpha   144.866
_cell_angle_beta   144.866
_cell_angle_gamma   50.534
_symmetry_Int_Tables_number   1
_cell_volume   1047.973
_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
  Pm  Pm0  1  0.846  0.952  0.377  1.0
  Pm  Pm1  1  0.575  0.469  0.623  1.0
  Pm  Pm2  1  0.166  0.166  0.000  1.0
  Pm  Pm3  1  0.875  0.506  0.131  1.0
  Pm  Pm4  1  0.175  0.298  0.394  1.0
  Pm  Pm5  1  0.584  0.084  0.500  1.0
  Pm  Pm6  1  0.904  0.781  0.606  1.0
  Pm  Pm7  1  0.375  0.744  0.869  1.0
  Pm  Pm8  1  0.219  0.825  0.123  1.0
  Pm  Pm9  1  0.916  0.416  0.500  1.0
  Pm  Pm10  1  0.494  0.625  0.369  1.0
  Pm  Pm11  1  0.256  0.125  0.631  1.0
  Pm  Pm12  1  0.702  0.096  0.877  1.0
  Pm  Pm13  1  0.834  0.834  0.000  1.0
  Pm  Pm14  1  0.531  0.154  0.106  1.0
  Pm  Pm15  1  0.048  0.425  0.894  1.0
  Se  Se16  1  0.507  0.114  0.253  1.0
  Se  Se17  1  0.074  0.827  0.610  1.0
  Se  Se18  1  0.861  0.253  0.747  1.0
  Se  Se19  1  0.889  0.136  0.892  1.0
  Se  Se20  1  0.243  0.997  0.108  1.0
  Se  Se21  1  0.676  0.786  0.253  1.0
  Se  Se22  1  0.217  0.464  0.390  1.0
  Se  Se23  1  0.842  0.437  0.246  1.0
  Se  Se24  1  0.533  0.423  0.747  1.0
  Se  Se25  1  0.404  0.158  0.595  1.0
  Se  Se26  1  0.191  0.596  0.754  1.0
  Se  Se27  1  0.214  0.467  0.890  1.0
  Se  Se28  1  0.577  0.324  0.110  1.0
  Se  Se29  1  0.003  0.111  0.247  1.0
  Se  Se30  1  0.563  0.809  0.405  1.0
  Se  Se31  1  0.173  0.783  0.247  1.0
  Se  Se32  1  0.864  0.757  0.753  1.0
  Se  Se33  1  0.747  0.493  0.608  1.0
  Se  Se34  1  0.536  0.926  0.753  1.0
  Se  Se35  1  0.559  0.813  0.905  1.0
  Se  Se36  1  0.908  0.654  0.095  1.0
  Se  Se37  1  0.346  0.441  0.254  1.0
  Se  Se38  1  0.886  0.139  0.392  1.0
  Se  Se39  1  0.187  0.092  0.746  1.0
[/CIF]
.