The crystal structure described by MgY2Se4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded to two equivalent Se(4) and three equivalent Se(1) atoms to form MgSe5 square pyramids that share corners with two equivalent Y(1)Se6 octahedra, corners with two equivalent Y(2)Se6 octahedra,  an edgeedge with one Y(1)Se6 octahedra, edges with three equivalent Y(2)Se6 octahedra, and edges with four equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 3-4°. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one Se(3), two equivalent Se(4), and three equivalent Se(2) atoms to form YSe6 octahedra that share corners with three equivalent Y(2)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Y(2)Se6 octahedra, edges with four equivalent Y(1)Se6 octahedra, and  an edgeedge with one Mg(1)Se5 square pyramid. The corner-sharing octahedral tilt angles range from 54-57°. In the second Y site, Y(2) is bonded to one Se(2), one Se(4), two equivalent Se(1), and two equivalent Se(3) atoms to form YSe6 octahedra that share corners with three equivalent Y(1)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Y(1)Se6 octahedra, edges with two equivalent Y(2)Se6 octahedra, and edges with three equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 54-57°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Mg(1) and two equivalent Y(2) atoms to form SeY2Mg3 square pyramids that share corners with two equivalent Se(4)Y3Mg2 square pyramids, edges with three equivalent Se(4)Y3Mg2 square pyramids, and edges with four equivalent Se(1)Y2Mg3 square pyramids. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Y(2) and three equivalent Y(1) atoms. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Y(1) and two equivalent Y(2) atoms. In the fourth Se site, Se(4) is bonded to two equivalent Mg(1), one Y(2), and two equivalent Y(1) atoms to form SeY3Mg2 square pyramids that share corners with two equivalent Se(1)Y2Mg3 square pyramids, edges with two equivalent Se(4)Y3Mg2 square pyramids, and edges with three equivalent Se(1)Y2Mg3 square pyramids. is represented by the Crystallographic Information File (CIF) [CIF]
data_Y2MgSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.023
_cell_length_b   13.194
_cell_length_c   14.147
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   750.980
_cell_formula_units_Z   4
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
  Y  Y0  1  0.250  0.116  0.073  1.0
  Y  Y1  1  0.750  0.884  0.927  1.0
  Y  Y2  1  0.750  0.384  0.573  1.0
  Y  Y3  1  0.250  0.616  0.427  1.0
  Y  Y4  1  0.250  0.143  0.702  1.0
  Y  Y5  1  0.750  0.857  0.298  1.0
  Y  Y6  1  0.750  0.357  0.202  1.0
  Y  Y7  1  0.250  0.643  0.798  1.0
  Mg  Mg8  1  0.750  0.109  0.456  1.0
  Mg  Mg9  1  0.250  0.891  0.544  1.0
  Mg  Mg10  1  0.250  0.391  0.956  1.0
  Mg  Mg11  1  0.750  0.609  0.044  1.0
  Se  Se12  1  0.750  0.008  0.618  1.0
  Se  Se13  1  0.250  0.992  0.382  1.0
  Se  Se14  1  0.250  0.492  0.118  1.0
  Se  Se15  1  0.750  0.508  0.882  1.0
  Se  Se16  1  0.250  0.028  0.881  1.0
  Se  Se17  1  0.750  0.972  0.119  1.0
  Se  Se18  1  0.750  0.472  0.381  1.0
  Se  Se19  1  0.250  0.528  0.619  1.0
  Se  Se20  1  0.250  0.221  0.248  1.0
  Se  Se21  1  0.750  0.779  0.752  1.0
  Se  Se22  1  0.750  0.279  0.748  1.0
  Se  Se23  1  0.250  0.721  0.252  1.0
  Se  Se24  1  0.750  0.261  0.013  1.0
  Se  Se25  1  0.250  0.739  0.987  1.0
  Se  Se26  1  0.250  0.239  0.513  1.0
  Se  Se27  1  0.750  0.761  0.487  1.0
[/CIF]
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The crystal structure described by MgY2Se4 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded to two equivalent Se(4) and three equivalent Se(1) atoms to form MgSe5 square pyramids that share corners with two equivalent Y(1)Se6 octahedra, corners with two equivalent Y(2)Se6 octahedra,  an edgeedge with one Y(1)Se6 octahedra, edges with three equivalent Y(2)Se6 octahedra, and edges with four equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 3-4°. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one Se(3), two equivalent Se(4), and three equivalent Se(2) atoms to form YSe6 octahedra that share corners with three equivalent Y(2)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Y(2)Se6 octahedra, edges with four equivalent Y(1)Se6 octahedra, and  an edgeedge with one Mg(1)Se5 square pyramid. The corner-sharing octahedral tilt angles range from 54-57°. In the second Y site, Y(2) is bonded to one Se(2), one Se(4), two equivalent Se(1), and two equivalent Se(3) atoms to form YSe6 octahedra that share corners with three equivalent Y(1)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Y(1)Se6 octahedra, edges with two equivalent Y(2)Se6 octahedra, and edges with three equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 54-57°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Mg(1) and two equivalent Y(2) atoms to form SeY2Mg3 square pyramids that share corners with two equivalent Se(4)Y3Mg2 square pyramids, edges with three equivalent Se(4)Y3Mg2 square pyramids, and edges with four equivalent Se(1)Y2Mg3 square pyramids. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Y(2) and three equivalent Y(1) atoms. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Y(1) and two equivalent Y(2) atoms. In the fourth Se site, Se(4) is bonded to two equivalent Mg(1), one Y(2), and two equivalent Y(1) atoms to form SeY3Mg2 square pyramids that share corners with two equivalent Se(1)Y2Mg3 square pyramids, edges with two equivalent Se(4)Y3Mg2 square pyramids, and edges with three equivalent Se(1)Y2Mg3 square pyramids. is represented by the Crystallographic Information File (CIF) [CIF]
data_Y2MgSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.023
_cell_length_b   13.194
_cell_length_c   14.147
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   750.980
_cell_formula_units_Z   4
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
  Y  Y0  1  0.250  0.116  0.073  1.0
  Y  Y1  1  0.750  0.884  0.927  1.0
  Y  Y2  1  0.750  0.384  0.573  1.0
  Y  Y3  1  0.250  0.616  0.427  1.0
  Y  Y4  1  0.250  0.143  0.702  1.0
  Y  Y5  1  0.750  0.857  0.298  1.0
  Y  Y6  1  0.750  0.357  0.202  1.0
  Y  Y7  1  0.250  0.643  0.798  1.0
  Mg  Mg8  1  0.750  0.109  0.456  1.0
  Mg  Mg9  1  0.250  0.891  0.544  1.0
  Mg  Mg10  1  0.250  0.391  0.956  1.0
  Mg  Mg11  1  0.750  0.609  0.044  1.0
  Se  Se12  1  0.750  0.008  0.618  1.0
  Se  Se13  1  0.250  0.992  0.382  1.0
  Se  Se14  1  0.250  0.492  0.118  1.0
  Se  Se15  1  0.750  0.508  0.882  1.0
  Se  Se16  1  0.250  0.028  0.881  1.0
  Se  Se17  1  0.750  0.972  0.119  1.0
  Se  Se18  1  0.750  0.472  0.381  1.0
  Se  Se19  1  0.250  0.528  0.619  1.0
  Se  Se20  1  0.250  0.221  0.248  1.0
  Se  Se21  1  0.750  0.779  0.752  1.0
  Se  Se22  1  0.750  0.279  0.748  1.0
  Se  Se23  1  0.250  0.721  0.252  1.0
  Se  Se24  1  0.750  0.261  0.013  1.0
  Se  Se25  1  0.250  0.739  0.987  1.0
  Se  Se26  1  0.250  0.239  0.513  1.0
  Se  Se27  1  0.750  0.761  0.487  1.0
[/CIF]
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