The material described by MgTbSe3 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form MgSe6 octahedra that share corners with eight equivalent Tb(1)Se4 tetrahedra and edges with three equivalent Mg(1)Se6 octahedra. Tb(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form TbSe4 tetrahedra that share corners with eight equivalent Mg(1)Se6 octahedra and  an edgeedge with one Tb(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-73°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one Tb(1) atom. In the second Se site, Se(2) is bonded to two equivalent Mg(1) and two equivalent Tb(1) atoms to form edge-sharing SeTb2Mg2 tetrahedra. is represented by the CIF file [CIF]
data_TbMgSe3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.351
_cell_length_b   7.351
_cell_length_c   6.884
_cell_angle_alpha   76.439
_cell_angle_beta   76.439
_cell_angle_gamma   118.683
_symmetry_Int_Tables_number   1
_cell_volume   289.830
_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
  Tb  Tb0  1  0.804  0.804  0.314  1.0
  Tb  Tb1  1  0.196  0.196  0.686  1.0
  Mg  Mg2  1  0.335  0.665  0.000  1.0
  Mg  Mg3  1  0.665  0.335  0.000  1.0
  Se  Se4  1  0.226  0.883  0.216  1.0
  Se  Se5  1  0.774  0.117  0.784  1.0
  Se  Se6  1  0.117  0.774  0.784  1.0
  Se  Se7  1  0.883  0.226  0.216  1.0
  Se  Se8  1  0.533  0.533  0.746  1.0
  Se  Se9  1  0.467  0.467  0.254  1.0
[/CIF]
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The material described by MgTbSe3 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form MgSe6 octahedra that share corners with eight equivalent Tb(1)Se4 tetrahedra and edges with three equivalent Mg(1)Se6 octahedra. Tb(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form TbSe4 tetrahedra that share corners with eight equivalent Mg(1)Se6 octahedra and  an edgeedge with one Tb(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-73°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one Tb(1) atom. In the second Se site, Se(2) is bonded to two equivalent Mg(1) and two equivalent Tb(1) atoms to form edge-sharing SeTb2Mg2 tetrahedra. is represented by the CIF file [CIF]
data_TbMgSe3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.351
_cell_length_b   7.351
_cell_length_c   6.884
_cell_angle_alpha   76.439
_cell_angle_beta   76.439
_cell_angle_gamma   118.683
_symmetry_Int_Tables_number   1
_cell_volume   289.830
_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
  Tb  Tb0  1  0.804  0.804  0.314  1.0
  Tb  Tb1  1  0.196  0.196  0.686  1.0
  Mg  Mg2  1  0.335  0.665  0.000  1.0
  Mg  Mg3  1  0.665  0.335  0.000  1.0
  Se  Se4  1  0.226  0.883  0.216  1.0
  Se  Se5  1  0.774  0.117  0.784  1.0
  Se  Se6  1  0.117  0.774  0.784  1.0
  Se  Se7  1  0.883  0.226  0.216  1.0
  Se  Se8  1  0.533  0.533  0.746  1.0
  Se  Se9  1  0.467  0.467  0.254  1.0
[/CIF]
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