The compound described by CeSe2 crystallizes in the triclinic P1 space group. There are three inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to one Se(1), one Se(2), one Se(4), one Se(6), and two equivalent Se(3) atoms to form distorted CeSe6 pentagonal pyramids that share  a cornercorner with one Ce(3)Se7 pentagonal bipyramid, corners with two equivalent Ce(2)Se7 pentagonal bipyramids, corners with two equivalent Ce(1)Se6 pentagonal pyramids, edges with two equivalent Ce(2)Se7 pentagonal bipyramids, and edges with three equivalent Ce(3)Se7 pentagonal bipyramids. In the second Ce site, Ce(2) is bonded to one Se(1), one Se(2), one Se(3), one Se(4), one Se(6), and two equivalent Se(5) atoms to form distorted CeSe7 pentagonal bipyramids that share corners with two equivalent Ce(2)Se7 pentagonal bipyramids, corners with two equivalent Ce(1)Se6 pentagonal pyramids, edges with four equivalent Ce(3)Se7 pentagonal bipyramids, and edges with two equivalent Ce(1)Se6 pentagonal pyramids. In the third Ce site, Ce(3) is bonded to one Se(1), one Se(2), one Se(3), one Se(5), one Se(6), and two equivalent Se(4) atoms to form distorted CeSe7 pentagonal bipyramids that share corners with two equivalent Ce(3)Se7 pentagonal bipyramids,  a cornercorner with one Ce(1)Se6 pentagonal pyramid, edges with four equivalent Ce(2)Se7 pentagonal bipyramids, and edges with three equivalent Ce(1)Se6 pentagonal pyramids. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one Ce(1), one Ce(2), and one Ce(3) atom. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one Ce(1), one Ce(2), and one Ce(3) atom. In the third Se site, Se(3) is bonded to one Ce(2), one Ce(3), and two equivalent Ce(1) atoms to form a mixture of corner and edge-sharing SeCe4 tetrahedra. In the fourth Se site, Se(4) is bonded to one Ce(1), one Ce(2), and two equivalent Ce(3) atoms to form a mixture of distorted corner and edge-sharing SeCe4 trigonal pyramids. In the fifth Se site, Se(5) is bonded in a trigonal non-coplanar geometry to one Ce(3) and two equivalent Ce(2) atoms. In the sixth Se site, Se(6) is bonded in a trigonal non-coplanar geometry to one Ce(1), one Ce(2), and one Ce(3) atom. is represented by the CIF file [CIF]
data_CeSe2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.509
_cell_length_b   7.273
_cell_length_c   7.663
_cell_angle_alpha   104.399
_cell_angle_beta   105.391
_cell_angle_gamma   107.705
_symmetry_Int_Tables_number   1
_cell_volume   263.245
_cell_formula_units_Z   3
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
  Ce  Ce0  1  0.927  0.430  0.467  1.0
  Ce  Ce1  1  0.270  0.689  0.092  1.0
  Ce  Ce2  1  0.756  0.986  0.761  1.0
  Se  Se3  1  0.502  0.072  0.424  1.0
  Se  Se4  1  0.811  0.338  0.070  1.0
  Se  Se5  1  0.481  0.581  0.440  1.0
  Se  Se6  1  0.196  0.839  0.764  1.0
  Se  Se7  1  0.810  0.815  0.067  1.0
  Se  Se8  1  0.192  0.335  0.776  1.0
[/CIF]
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The compound described by CeSe2 crystallizes in the triclinic P1 space group. There are three inequivalent Ce sites. In the first Ce site, Ce(1) is bonded to one Se(1), one Se(2), one Se(4), one Se(6), and two equivalent Se(3) atoms to form distorted CeSe6 pentagonal pyramids that share  a cornercorner with one Ce(3)Se7 pentagonal bipyramid, corners with two equivalent Ce(2)Se7 pentagonal bipyramids, corners with two equivalent Ce(1)Se6 pentagonal pyramids, edges with two equivalent Ce(2)Se7 pentagonal bipyramids, and edges with three equivalent Ce(3)Se7 pentagonal bipyramids. In the second Ce site, Ce(2) is bonded to one Se(1), one Se(2), one Se(3), one Se(4), one Se(6), and two equivalent Se(5) atoms to form distorted CeSe7 pentagonal bipyramids that share corners with two equivalent Ce(2)Se7 pentagonal bipyramids, corners with two equivalent Ce(1)Se6 pentagonal pyramids, edges with four equivalent Ce(3)Se7 pentagonal bipyramids, and edges with two equivalent Ce(1)Se6 pentagonal pyramids. In the third Ce site, Ce(3) is bonded to one Se(1), one Se(2), one Se(3), one Se(5), one Se(6), and two equivalent Se(4) atoms to form distorted CeSe7 pentagonal bipyramids that share corners with two equivalent Ce(3)Se7 pentagonal bipyramids,  a cornercorner with one Ce(1)Se6 pentagonal pyramid, edges with four equivalent Ce(2)Se7 pentagonal bipyramids, and edges with three equivalent Ce(1)Se6 pentagonal pyramids. There are six inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one Ce(1), one Ce(2), and one Ce(3) atom. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one Ce(1), one Ce(2), and one Ce(3) atom. In the third Se site, Se(3) is bonded to one Ce(2), one Ce(3), and two equivalent Ce(1) atoms to form a mixture of corner and edge-sharing SeCe4 tetrahedra. In the fourth Se site, Se(4) is bonded to one Ce(1), one Ce(2), and two equivalent Ce(3) atoms to form a mixture of distorted corner and edge-sharing SeCe4 trigonal pyramids. In the fifth Se site, Se(5) is bonded in a trigonal non-coplanar geometry to one Ce(3) and two equivalent Ce(2) atoms. In the sixth Se site, Se(6) is bonded in a trigonal non-coplanar geometry to one Ce(1), one Ce(2), and one Ce(3) atom. is represented by the CIF file [CIF]
data_CeSe2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.509
_cell_length_b   7.273
_cell_length_c   7.663
_cell_angle_alpha   104.399
_cell_angle_beta   105.391
_cell_angle_gamma   107.705
_symmetry_Int_Tables_number   1
_cell_volume   263.245
_cell_formula_units_Z   3
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
  Ce  Ce0  1  0.927  0.430  0.467  1.0
  Ce  Ce1  1  0.270  0.689  0.092  1.0
  Ce  Ce2  1  0.756  0.986  0.761  1.0
  Se  Se3  1  0.502  0.072  0.424  1.0
  Se  Se4  1  0.811  0.338  0.070  1.0
  Se  Se5  1  0.481  0.581  0.440  1.0
  Se  Se6  1  0.196  0.839  0.764  1.0
  Se  Se7  1  0.810  0.815  0.067  1.0
  Se  Se8  1  0.192  0.335  0.776  1.0
[/CIF]
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