The crystal structure described by MgErS3 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form MgS6 octahedra that share corners with eight equivalent Er(1)S4 tetrahedra and edges with three equivalent Mg(1)S6 octahedra. Er(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form ErS4 tetrahedra that share corners with eight equivalent Mg(1)S6 octahedra and  an edgeedge with one Er(1)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-73°. There are two inequivalent S sites. In the first S site, S(1) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one Er(1) atom. In the second S site, S(2) is bonded to two equivalent Mg(1) and two equivalent Er(1) atoms to form edge-sharing SEr2Mg2 tetrahedra. is represented by the CIF card [CIF]
data_ErMgS3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.962
_cell_length_b   6.962
_cell_length_c   6.650
_cell_angle_alpha   76.932
_cell_angle_beta   76.932
_cell_angle_gamma   119.280
_symmetry_Int_Tables_number   1
_cell_volume   251.451
_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  0.198  0.198  0.678  1.0
  Er  Er1  1  0.802  0.802  0.322  1.0
  Mg  Mg2  1  0.338  0.662  0.000  1.0
  Mg  Mg3  1  0.662  0.338  0.000  1.0
  S  S4  1  0.114  0.777  0.800  1.0
  S  S5  1  0.886  0.223  0.200  1.0
  S  S6  1  0.223  0.886  0.200  1.0
  S  S7  1  0.777  0.114  0.800  1.0
  S  S8  1  0.468  0.468  0.257  1.0
  S  S9  1  0.532  0.532  0.743  1.0
[/CIF]
.
The crystal structure described by MgErS3 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form MgS6 octahedra that share corners with eight equivalent Er(1)S4 tetrahedra and edges with three equivalent Mg(1)S6 octahedra. Er(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form ErS4 tetrahedra that share corners with eight equivalent Mg(1)S6 octahedra and  an edgeedge with one Er(1)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 54-73°. There are two inequivalent S sites. In the first S site, S(1) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one Er(1) atom. In the second S site, S(2) is bonded to two equivalent Mg(1) and two equivalent Er(1) atoms to form edge-sharing SEr2Mg2 tetrahedra. is represented by the CIF card [CIF]
data_ErMgS3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.962
_cell_length_b   6.962
_cell_length_c   6.650
_cell_angle_alpha   76.932
_cell_angle_beta   76.932
_cell_angle_gamma   119.280
_symmetry_Int_Tables_number   1
_cell_volume   251.451
_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  0.198  0.198  0.678  1.0
  Er  Er1  1  0.802  0.802  0.322  1.0
  Mg  Mg2  1  0.338  0.662  0.000  1.0
  Mg  Mg3  1  0.662  0.338  0.000  1.0
  S  S4  1  0.114  0.777  0.800  1.0
  S  S5  1  0.886  0.223  0.200  1.0
  S  S6  1  0.223  0.886  0.200  1.0
  S  S7  1  0.777  0.114  0.800  1.0
  S  S8  1  0.468  0.468  0.257  1.0
  S  S9  1  0.532  0.532  0.743  1.0
[/CIF]
.