The compound described by MgNdSe3 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 Nd(1)Se4 tetrahedra and edges with three equivalent Mg(1)Se6 octahedra. Nd(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted NdSe4 tetrahedra that share corners with eight equivalent Mg(1)Se6 octahedra and  an edgeedge with one Nd(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-73°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mg(1) and one Nd(1) atom. In the second Se site, Se(2) is bonded to two equivalent Mg(1) and two equivalent Nd(1) atoms to form edge-sharing SeNd2Mg2 tetrahedra. is represented by the CIF card [CIF]
data_NdMgSe3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.367
_cell_length_b   7.367
_cell_length_c   6.852
_cell_angle_alpha   76.280
_cell_angle_beta   76.280
_cell_angle_gamma   115.816
_symmetry_Int_Tables_number   1
_cell_volume   299.530
_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
  Nd  Nd0  1  0.804  0.804  0.315  1.0
  Nd  Nd1  1  0.196  0.196  0.685  1.0
  Mg  Mg2  1  0.332  0.668  0.000  1.0
  Mg  Mg3  1  0.668  0.332  0.000  1.0
  Se  Se4  1  0.238  0.894  0.219  1.0
  Se  Se5  1  0.762  0.106  0.781  1.0
  Se  Se6  1  0.106  0.762  0.781  1.0
  Se  Se7  1  0.894  0.238  0.219  1.0
  Se  Se8  1  0.527  0.527  0.749  1.0
  Se  Se9  1  0.473  0.473  0.251  1.0
[/CIF]
.
The compound described by MgNdSe3 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 Nd(1)Se4 tetrahedra and edges with three equivalent Mg(1)Se6 octahedra. Nd(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted NdSe4 tetrahedra that share corners with eight equivalent Mg(1)Se6 octahedra and  an edgeedge with one Nd(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-73°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Mg(1) and one Nd(1) atom. In the second Se site, Se(2) is bonded to two equivalent Mg(1) and two equivalent Nd(1) atoms to form edge-sharing SeNd2Mg2 tetrahedra. is represented by the CIF card [CIF]
data_NdMgSe3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   7.367
_cell_length_b   7.367
_cell_length_c   6.852
_cell_angle_alpha   76.280
_cell_angle_beta   76.280
_cell_angle_gamma   115.816
_symmetry_Int_Tables_number   1
_cell_volume   299.530
_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
  Nd  Nd0  1  0.804  0.804  0.315  1.0
  Nd  Nd1  1  0.196  0.196  0.685  1.0
  Mg  Mg2  1  0.332  0.668  0.000  1.0
  Mg  Mg3  1  0.668  0.332  0.000  1.0
  Se  Se4  1  0.238  0.894  0.219  1.0
  Se  Se5  1  0.762  0.106  0.781  1.0
  Se  Se6  1  0.106  0.762  0.781  1.0
  Se  Se7  1  0.894  0.238  0.219  1.0
  Se  Se8  1  0.527  0.527  0.749  1.0
  Se  Se9  1  0.473  0.473  0.251  1.0
[/CIF]
.