The material described by MgYb2Se4 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Se(2), one Se(3), one Se(5), one Se(6), and two equivalent Se(4) atoms to form MgSe6 octahedra that share corners with two equivalent Yb(3)Se6 octahedra, corners with two equivalent Yb(4)Se6 octahedra,  an edgeedge with one Mg(1)Se6 octahedra, edges with two equivalent Yb(3)Se6 octahedra, edges with two equivalent Yb(4)Se6 octahedra, and edges with three equivalent Yb(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-11°. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Se(1), one Se(2), one Se(6), one Se(7), and two equivalent Se(8) atoms. There are four inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to one Se(1), one Se(4), one Se(5), one Se(6), and two equivalent Se(3) atoms to form YbSe6 octahedra that share corners with two equivalent Yb(3)Se6 octahedra, corners with two equivalent Yb(4)Se6 octahedra,  an edgeedge with one Yb(1)Se6 octahedra, edges with two equivalent Yb(3)Se6 octahedra, edges with two equivalent Yb(4)Se6 octahedra, and edges with three equivalent Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-11°. In the second Yb site, Yb(2) is bonded in a 8-coordinate geometry to one Se(3), one Se(8), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(7) atoms. In the third Yb site, Yb(3) is bonded to one Se(3), one Se(4), one Se(5), one Se(8), and two equivalent Se(6) atoms to form YbSe6 octahedra that share corners with two equivalent Mg(1)Se6 octahedra, corners with two equivalent Yb(1)Se6 octahedra,  an edgeedge with one Yb(3)Se6 octahedra, edges with two equivalent Mg(1)Se6 octahedra, edges with two equivalent Yb(1)Se6 octahedra, and edges with three equivalent Yb(4)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-11°. In the fourth Yb site, Yb(4) is bonded to one Se(3), one Se(4), one Se(6), one Se(7), and two equivalent Se(5) atoms to form YbSe6 octahedra that share corners with two equivalent Mg(1)Se6 octahedra, corners with two equivalent Yb(1)Se6 octahedra,  an edgeedge with one Yb(4)Se6 octahedra, edges with two equivalent Mg(1)Se6 octahedra, edges with two equivalent Yb(1)Se6 octahedra, and edges with three equivalent Yb(3)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-11°. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(1), two equivalent Yb(2), and one Se(1) atom. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(2), two equivalent Yb(2), and one Se(2) atom. In the third Se site, Se(3) is bonded to one Mg(1), one Yb(2), one Yb(3), one Yb(4), and two equivalent Yb(1) atoms to form SeYb5Mg octahedra that share corners with two equivalent Se(6)Yb4Mg2 octahedra, corners with two equivalent Se(5)Yb4Mg square pyramids,  an edgeedge with one Se(3)Yb5Mg octahedra, edges with two equivalent Se(6)Yb4Mg2 octahedra, edges with two equivalent Se(5)Yb4Mg square pyramids, and edges with three equivalent Se(4)Yb3Mg2 square pyramids. The corner-sharing octahedral tilt angles range from 5-6°. In the fourth Se site, Se(4) is bonded to two equivalent Mg(1), one Yb(1), one Yb(3), and one Yb(4) atom to form SeYb3Mg2 square pyramids that share corners with two equivalent Se(6)Yb4Mg2 octahedra, corners with two equivalent Se(5)Yb4Mg square pyramids, edges with two equivalent Se(6)Yb4Mg2 octahedra, edges with three equivalent Se(3)Yb5Mg octahedra,  an edgeedge with one Se(4)Yb3Mg2 square pyramid, and edges with two equivalent Se(5)Yb4Mg square pyramids. The corner-sharing octahedral tilt angles range from 6-7°. In the fifth Se site, Se(5) is bonded to one Mg(1), one Yb(1), one Yb(3), and two equivalent Yb(4) atoms to form SeYb4Mg square pyramids that share corners with two equivalent Se(3)Yb5Mg octahedra, corners with two equivalent Se(4)Yb3Mg2 square pyramids, edges with two equivalent Se(3)Yb5Mg octahedra, edges with three equivalent Se(6)Yb4Mg2 octahedra,  an edgeedge with one Se(5)Yb4Mg square pyramid, and edges with two equivalent Se(4)Yb3Mg2 square pyramids. The corner-sharing octahedral tilt angles are 9°. In the sixth Se site, Se(6) is bonded to one Mg(1), one Mg(2), one Yb(1), one Yb(4), and two equivalent Yb(3) atoms to form SeYb4Mg2 octahedra that share corners with two equivalent Se(3)Yb5Mg octahedra, corners with two equivalent Se(4)Yb3Mg2 square pyramids,  an edgeedge with one Se(6)Yb4Mg2 octahedra, edges with two equivalent Se(3)Yb5Mg octahedra, edges with two equivalent Se(4)Yb3Mg2 square pyramids, and edges with three equivalent Se(5)Yb4Mg square pyramids. The corner-sharing octahedral tilt angles range from 5-6°. In the seventh Se site, Se(7) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(4), two equivalent Yb(2), and one Se(8) atom. In the eighth Se site, Se(8) is bonded in a 5-coordinate geometry to two equivalent Mg(2), one Yb(2), one Yb(3), and one Se(7) atom. is represented by the CIF card [CIF]
data_Yb2MgSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.137
_cell_length_b   8.202
_cell_length_c   11.100
_cell_angle_alpha   78.739
_cell_angle_beta   84.263
_cell_angle_gamma   116.182
_symmetry_Int_Tables_number   1
_cell_volume   715.597
_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
  Yb  Yb0  1  0.086  0.647  0.624  1.0
  Yb  Yb1  1  0.914  0.353  0.376  1.0
  Yb  Yb2  1  0.198  0.823  0.062  1.0
  Yb  Yb3  1  0.802  0.177  0.938  1.0
  Yb  Yb4  1  0.411  0.620  0.366  1.0
  Yb  Yb5  1  0.589  0.380  0.634  1.0
  Yb  Yb6  1  0.417  0.120  0.360  1.0
  Yb  Yb7  1  0.583  0.880  0.640  1.0
  Mg  Mg8  1  0.091  0.126  0.624  1.0
  Mg  Mg9  1  0.909  0.874  0.376  1.0
  Mg  Mg10  1  0.316  0.445  0.902  1.0
  Mg  Mg11  1  0.684  0.555  0.098  1.0
  Se  Se12  1  0.091  0.569  0.898  1.0
  Se  Se13  1  0.909  0.431  0.102  1.0
  Se  Se14  1  0.105  0.089  0.902  1.0
  Se  Se15  1  0.895  0.911  0.098  1.0
  Se  Se16  1  0.155  0.750  0.346  1.0
  Se  Se17  1  0.845  0.250  0.654  1.0
  Se  Se18  1  0.160  0.232  0.370  1.0
  Se  Se19  1  0.840  0.768  0.630  1.0
  Se  Se20  1  0.333  0.015  0.632  1.0
  Se  Se21  1  0.667  0.985  0.368  1.0
  Se  Se22  1  0.329  0.498  0.645  1.0
  Se  Se23  1  0.671  0.502  0.355  1.0
  Se  Se24  1  0.485  0.158  0.086  1.0
  Se  Se25  1  0.515  0.842  0.914  1.0
  Se  Se26  1  0.393  0.582  0.104  1.0
  Se  Se27  1  0.607  0.418  0.896  1.0
[/CIF]
.
The material described by MgYb2Se4 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Se(2), one Se(3), one Se(5), one Se(6), and two equivalent Se(4) atoms to form MgSe6 octahedra that share corners with two equivalent Yb(3)Se6 octahedra, corners with two equivalent Yb(4)Se6 octahedra,  an edgeedge with one Mg(1)Se6 octahedra, edges with two equivalent Yb(3)Se6 octahedra, edges with two equivalent Yb(4)Se6 octahedra, and edges with three equivalent Yb(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-11°. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Se(1), one Se(2), one Se(6), one Se(7), and two equivalent Se(8) atoms. There are four inequivalent Yb sites. In the first Yb site, Yb(1) is bonded to one Se(1), one Se(4), one Se(5), one Se(6), and two equivalent Se(3) atoms to form YbSe6 octahedra that share corners with two equivalent Yb(3)Se6 octahedra, corners with two equivalent Yb(4)Se6 octahedra,  an edgeedge with one Yb(1)Se6 octahedra, edges with two equivalent Yb(3)Se6 octahedra, edges with two equivalent Yb(4)Se6 octahedra, and edges with three equivalent Mg(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-11°. In the second Yb site, Yb(2) is bonded in a 8-coordinate geometry to one Se(3), one Se(8), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(7) atoms. In the third Yb site, Yb(3) is bonded to one Se(3), one Se(4), one Se(5), one Se(8), and two equivalent Se(6) atoms to form YbSe6 octahedra that share corners with two equivalent Mg(1)Se6 octahedra, corners with two equivalent Yb(1)Se6 octahedra,  an edgeedge with one Yb(3)Se6 octahedra, edges with two equivalent Mg(1)Se6 octahedra, edges with two equivalent Yb(1)Se6 octahedra, and edges with three equivalent Yb(4)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-11°. In the fourth Yb site, Yb(4) is bonded to one Se(3), one Se(4), one Se(6), one Se(7), and two equivalent Se(5) atoms to form YbSe6 octahedra that share corners with two equivalent Mg(1)Se6 octahedra, corners with two equivalent Yb(1)Se6 octahedra,  an edgeedge with one Yb(4)Se6 octahedra, edges with two equivalent Mg(1)Se6 octahedra, edges with two equivalent Yb(1)Se6 octahedra, and edges with three equivalent Yb(3)Se6 octahedra. The corner-sharing octahedral tilt angles range from 2-11°. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(1), two equivalent Yb(2), and one Se(1) atom. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(2), two equivalent Yb(2), and one Se(2) atom. In the third Se site, Se(3) is bonded to one Mg(1), one Yb(2), one Yb(3), one Yb(4), and two equivalent Yb(1) atoms to form SeYb5Mg octahedra that share corners with two equivalent Se(6)Yb4Mg2 octahedra, corners with two equivalent Se(5)Yb4Mg square pyramids,  an edgeedge with one Se(3)Yb5Mg octahedra, edges with two equivalent Se(6)Yb4Mg2 octahedra, edges with two equivalent Se(5)Yb4Mg square pyramids, and edges with three equivalent Se(4)Yb3Mg2 square pyramids. The corner-sharing octahedral tilt angles range from 5-6°. In the fourth Se site, Se(4) is bonded to two equivalent Mg(1), one Yb(1), one Yb(3), and one Yb(4) atom to form SeYb3Mg2 square pyramids that share corners with two equivalent Se(6)Yb4Mg2 octahedra, corners with two equivalent Se(5)Yb4Mg square pyramids, edges with two equivalent Se(6)Yb4Mg2 octahedra, edges with three equivalent Se(3)Yb5Mg octahedra,  an edgeedge with one Se(4)Yb3Mg2 square pyramid, and edges with two equivalent Se(5)Yb4Mg square pyramids. The corner-sharing octahedral tilt angles range from 6-7°. In the fifth Se site, Se(5) is bonded to one Mg(1), one Yb(1), one Yb(3), and two equivalent Yb(4) atoms to form SeYb4Mg square pyramids that share corners with two equivalent Se(3)Yb5Mg octahedra, corners with two equivalent Se(4)Yb3Mg2 square pyramids, edges with two equivalent Se(3)Yb5Mg octahedra, edges with three equivalent Se(6)Yb4Mg2 octahedra,  an edgeedge with one Se(5)Yb4Mg square pyramid, and edges with two equivalent Se(4)Yb3Mg2 square pyramids. The corner-sharing octahedral tilt angles are 9°. In the sixth Se site, Se(6) is bonded to one Mg(1), one Mg(2), one Yb(1), one Yb(4), and two equivalent Yb(3) atoms to form SeYb4Mg2 octahedra that share corners with two equivalent Se(3)Yb5Mg octahedra, corners with two equivalent Se(4)Yb3Mg2 square pyramids,  an edgeedge with one Se(6)Yb4Mg2 octahedra, edges with two equivalent Se(3)Yb5Mg octahedra, edges with two equivalent Se(4)Yb3Mg2 square pyramids, and edges with three equivalent Se(5)Yb4Mg square pyramids. The corner-sharing octahedral tilt angles range from 5-6°. In the seventh Se site, Se(7) is bonded in a 5-coordinate geometry to one Mg(2), one Yb(4), two equivalent Yb(2), and one Se(8) atom. In the eighth Se site, Se(8) is bonded in a 5-coordinate geometry to two equivalent Mg(2), one Yb(2), one Yb(3), and one Se(7) atom. is represented by the CIF card [CIF]
data_Yb2MgSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.137
_cell_length_b   8.202
_cell_length_c   11.100
_cell_angle_alpha   78.739
_cell_angle_beta   84.263
_cell_angle_gamma   116.182
_symmetry_Int_Tables_number   1
_cell_volume   715.597
_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
  Yb  Yb0  1  0.086  0.647  0.624  1.0
  Yb  Yb1  1  0.914  0.353  0.376  1.0
  Yb  Yb2  1  0.198  0.823  0.062  1.0
  Yb  Yb3  1  0.802  0.177  0.938  1.0
  Yb  Yb4  1  0.411  0.620  0.366  1.0
  Yb  Yb5  1  0.589  0.380  0.634  1.0
  Yb  Yb6  1  0.417  0.120  0.360  1.0
  Yb  Yb7  1  0.583  0.880  0.640  1.0
  Mg  Mg8  1  0.091  0.126  0.624  1.0
  Mg  Mg9  1  0.909  0.874  0.376  1.0
  Mg  Mg10  1  0.316  0.445  0.902  1.0
  Mg  Mg11  1  0.684  0.555  0.098  1.0
  Se  Se12  1  0.091  0.569  0.898  1.0
  Se  Se13  1  0.909  0.431  0.102  1.0
  Se  Se14  1  0.105  0.089  0.902  1.0
  Se  Se15  1  0.895  0.911  0.098  1.0
  Se  Se16  1  0.155  0.750  0.346  1.0
  Se  Se17  1  0.845  0.250  0.654  1.0
  Se  Se18  1  0.160  0.232  0.370  1.0
  Se  Se19  1  0.840  0.768  0.630  1.0
  Se  Se20  1  0.333  0.015  0.632  1.0
  Se  Se21  1  0.667  0.985  0.368  1.0
  Se  Se22  1  0.329  0.498  0.645  1.0
  Se  Se23  1  0.671  0.502  0.355  1.0
  Se  Se24  1  0.485  0.158  0.086  1.0
  Se  Se25  1  0.515  0.842  0.914  1.0
  Se  Se26  1  0.393  0.582  0.104  1.0
  Se  Se27  1  0.607  0.418  0.896  1.0
[/CIF]
.