The crystal structure described by MgEu2Se4 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 Eu(1)Se6 octahedra, corners with two equivalent Eu(2)Se6 octahedra,  an edgeedge with one Eu(1)Se6 octahedra, edges with three equivalent Eu(2)Se6 octahedra, and edges with four equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 6-7°. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to one Se(3), two equivalent Se(4), and three equivalent Se(2) atoms to form EuSe6 octahedra that share corners with three equivalent Eu(2)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Eu(2)Se6 octahedra, edges with four equivalent Eu(1)Se6 octahedra, and  an edgeedge with one Mg(1)Se5 square pyramid. The corner-sharing octahedral tilt angles range from 59-61°. In the second Eu site, Eu(2) is bonded to one Se(2), one Se(4), two equivalent Se(1), and two equivalent Se(3) atoms to form EuSe6 octahedra that share corners with three equivalent Eu(1)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Eu(1)Se6 octahedra, edges with two equivalent Eu(2)Se6 octahedra, and edges with three equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 59-61°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Mg(1) and two equivalent Eu(2) atoms to form SeEu2Mg3 square pyramids that share corners with two equivalent Se(4)Eu3Mg2 square pyramids, corners with two equivalent Se(2)Eu4 tetrahedra, edges with three equivalent Se(4)Eu3Mg2 square pyramids, and edges with four equivalent Se(1)Eu2Mg3 square pyramids. In the second Se site, Se(2) is bonded to one Eu(2) and three equivalent Eu(1) atoms to form distorted SeEu4 tetrahedra that share corners with two equivalent Se(1)Eu2Mg3 square pyramids, corners with five equivalent Se(4)Eu3Mg2 square pyramids, corners with two equivalent Se(2)Eu4 tetrahedra,  an edgeedge with one Se(4)Eu3Mg2 square pyramid, and edges with two equivalent Se(2)Eu4 tetrahedra. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Eu(1) and two equivalent Eu(2) atoms. In the fourth Se site, Se(4) is bonded to two equivalent Mg(1), one Eu(2), and two equivalent Eu(1) atoms to form SeEu3Mg2 square pyramids that share corners with two equivalent Se(1)Eu2Mg3 square pyramids, corners with five equivalent Se(2)Eu4 tetrahedra, edges with two equivalent Se(4)Eu3Mg2 square pyramids, edges with three equivalent Se(1)Eu2Mg3 square pyramids, and  an edgeedge with one Se(2)Eu4 tetrahedra. is represented by the CIF file [CIF]
data_Eu2MgSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.097
_cell_length_b   4.127
_cell_length_c   13.799
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   802.757
_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
  Eu  Eu0  1  0.123  0.250  0.072  1.0
  Eu  Eu1  1  0.877  0.750  0.928  1.0
  Eu  Eu2  1  0.377  0.750  0.572  1.0
  Eu  Eu3  1  0.623  0.250  0.428  1.0
  Eu  Eu4  1  0.127  0.250  0.706  1.0
  Eu  Eu5  1  0.873  0.750  0.294  1.0
  Eu  Eu6  1  0.373  0.750  0.206  1.0
  Eu  Eu7  1  0.627  0.250  0.794  1.0
  Mg  Mg8  1  0.105  0.750  0.463  1.0
  Mg  Mg9  1  0.895  0.250  0.537  1.0
  Mg  Mg10  1  0.395  0.250  0.963  1.0
  Mg  Mg11  1  0.605  0.750  0.037  1.0
  Se  Se12  1  0.998  0.750  0.621  1.0
  Se  Se13  1  0.002  0.250  0.379  1.0
  Se  Se14  1  0.502  0.250  0.121  1.0
  Se  Se15  1  0.498  0.750  0.879  1.0
  Se  Se16  1  0.019  0.250  0.887  1.0
  Se  Se17  1  0.981  0.750  0.113  1.0
  Se  Se18  1  0.481  0.750  0.387  1.0
  Se  Se19  1  0.519  0.250  0.613  1.0
  Se  Se20  1  0.236  0.250  0.252  1.0
  Se  Se21  1  0.764  0.750  0.748  1.0
  Se  Se22  1  0.264  0.750  0.752  1.0
  Se  Se23  1  0.736  0.250  0.248  1.0
  Se  Se24  1  0.271  0.750  0.007  1.0
  Se  Se25  1  0.729  0.250  0.993  1.0
  Se  Se26  1  0.229  0.250  0.507  1.0
  Se  Se27  1  0.771  0.750  0.493  1.0
[/CIF]
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The crystal structure described by MgEu2Se4 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 Eu(1)Se6 octahedra, corners with two equivalent Eu(2)Se6 octahedra,  an edgeedge with one Eu(1)Se6 octahedra, edges with three equivalent Eu(2)Se6 octahedra, and edges with four equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 6-7°. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to one Se(3), two equivalent Se(4), and three equivalent Se(2) atoms to form EuSe6 octahedra that share corners with three equivalent Eu(2)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Eu(2)Se6 octahedra, edges with four equivalent Eu(1)Se6 octahedra, and  an edgeedge with one Mg(1)Se5 square pyramid. The corner-sharing octahedral tilt angles range from 59-61°. In the second Eu site, Eu(2) is bonded to one Se(2), one Se(4), two equivalent Se(1), and two equivalent Se(3) atoms to form EuSe6 octahedra that share corners with three equivalent Eu(1)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Eu(1)Se6 octahedra, edges with two equivalent Eu(2)Se6 octahedra, and edges with three equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 59-61°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Mg(1) and two equivalent Eu(2) atoms to form SeEu2Mg3 square pyramids that share corners with two equivalent Se(4)Eu3Mg2 square pyramids, corners with two equivalent Se(2)Eu4 tetrahedra, edges with three equivalent Se(4)Eu3Mg2 square pyramids, and edges with four equivalent Se(1)Eu2Mg3 square pyramids. In the second Se site, Se(2) is bonded to one Eu(2) and three equivalent Eu(1) atoms to form distorted SeEu4 tetrahedra that share corners with two equivalent Se(1)Eu2Mg3 square pyramids, corners with five equivalent Se(4)Eu3Mg2 square pyramids, corners with two equivalent Se(2)Eu4 tetrahedra,  an edgeedge with one Se(4)Eu3Mg2 square pyramid, and edges with two equivalent Se(2)Eu4 tetrahedra. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Eu(1) and two equivalent Eu(2) atoms. In the fourth Se site, Se(4) is bonded to two equivalent Mg(1), one Eu(2), and two equivalent Eu(1) atoms to form SeEu3Mg2 square pyramids that share corners with two equivalent Se(1)Eu2Mg3 square pyramids, corners with five equivalent Se(2)Eu4 tetrahedra, edges with two equivalent Se(4)Eu3Mg2 square pyramids, edges with three equivalent Se(1)Eu2Mg3 square pyramids, and  an edgeedge with one Se(2)Eu4 tetrahedra. is represented by the CIF file [CIF]
data_Eu2MgSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   14.097
_cell_length_b   4.127
_cell_length_c   13.799
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   802.757
_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
  Eu  Eu0  1  0.123  0.250  0.072  1.0
  Eu  Eu1  1  0.877  0.750  0.928  1.0
  Eu  Eu2  1  0.377  0.750  0.572  1.0
  Eu  Eu3  1  0.623  0.250  0.428  1.0
  Eu  Eu4  1  0.127  0.250  0.706  1.0
  Eu  Eu5  1  0.873  0.750  0.294  1.0
  Eu  Eu6  1  0.373  0.750  0.206  1.0
  Eu  Eu7  1  0.627  0.250  0.794  1.0
  Mg  Mg8  1  0.105  0.750  0.463  1.0
  Mg  Mg9  1  0.895  0.250  0.537  1.0
  Mg  Mg10  1  0.395  0.250  0.963  1.0
  Mg  Mg11  1  0.605  0.750  0.037  1.0
  Se  Se12  1  0.998  0.750  0.621  1.0
  Se  Se13  1  0.002  0.250  0.379  1.0
  Se  Se14  1  0.502  0.250  0.121  1.0
  Se  Se15  1  0.498  0.750  0.879  1.0
  Se  Se16  1  0.019  0.250  0.887  1.0
  Se  Se17  1  0.981  0.750  0.113  1.0
  Se  Se18  1  0.481  0.750  0.387  1.0
  Se  Se19  1  0.519  0.250  0.613  1.0
  Se  Se20  1  0.236  0.250  0.252  1.0
  Se  Se21  1  0.764  0.750  0.748  1.0
  Se  Se22  1  0.264  0.750  0.752  1.0
  Se  Se23  1  0.736  0.250  0.248  1.0
  Se  Se24  1  0.271  0.750  0.007  1.0
  Se  Se25  1  0.729  0.250  0.993  1.0
  Se  Se26  1  0.229  0.250  0.507  1.0
  Se  Se27  1  0.771  0.750  0.493  1.0
[/CIF]
.