The material structure described by MgErSe3 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 Er(1)Se4 tetrahedra and edges with three equivalent Mg(1)Se6 octahedra. Er(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form ErSe4 tetrahedra that share corners with eight equivalent Mg(1)Se6 octahedra and  an edgeedge with one Er(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-72°. 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 Er(1) atom. In the second Se site, Se(2) is bonded to two equivalent Mg(1) and two equivalent Er(1) atoms to form edge-sharing SeEr2Mg2 tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_ErMgSe3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.367
_cell_length_b   7.367
_cell_length_c   6.928
_cell_angle_alpha   76.646
_cell_angle_beta   76.646
_cell_angle_gamma   120.378
_symmetry_Int_Tables_number   1
_cell_volume   287.227
_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  0.805  0.805  0.318  1.0
  Er  Er1  1  0.195  0.195  0.682  1.0
  Mg  Mg2  1  0.336  0.664  0.000  1.0
  Mg  Mg3  1  0.664  0.336  0.000  1.0
  Se  Se4  1  0.221  0.878  0.215  1.0
  Se  Se5  1  0.779  0.122  0.785  1.0
  Se  Se6  1  0.122  0.779  0.785  1.0
  Se  Se7  1  0.878  0.221  0.215  1.0
  Se  Se8  1  0.532  0.532  0.746  1.0
  Se  Se9  1  0.468  0.468  0.254  1.0
[/CIF]
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The material structure described by MgErSe3 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 Er(1)Se4 tetrahedra and edges with three equivalent Mg(1)Se6 octahedra. Er(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form ErSe4 tetrahedra that share corners with eight equivalent Mg(1)Se6 octahedra and  an edgeedge with one Er(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-72°. 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 Er(1) atom. In the second Se site, Se(2) is bonded to two equivalent Mg(1) and two equivalent Er(1) atoms to form edge-sharing SeEr2Mg2 tetrahedra. is represented by the Crystallographic Information File (CIF) [CIF]
data_ErMgSe3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.367
_cell_length_b   7.367
_cell_length_c   6.928
_cell_angle_alpha   76.646
_cell_angle_beta   76.646
_cell_angle_gamma   120.378
_symmetry_Int_Tables_number   1
_cell_volume   287.227
_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  0.805  0.805  0.318  1.0
  Er  Er1  1  0.195  0.195  0.682  1.0
  Mg  Mg2  1  0.336  0.664  0.000  1.0
  Mg  Mg3  1  0.664  0.336  0.000  1.0
  Se  Se4  1  0.221  0.878  0.215  1.0
  Se  Se5  1  0.779  0.122  0.785  1.0
  Se  Se6  1  0.122  0.779  0.785  1.0
  Se  Se7  1  0.878  0.221  0.215  1.0
  Se  Se8  1  0.532  0.532  0.746  1.0
  Se  Se9  1  0.468  0.468  0.254  1.0
[/CIF]
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