The compound described by MgPm2Se4 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 Pm(1)Se6 octahedra, corners with two equivalent Pm(2)Se6 octahedra,  an edgeedge with one Pm(1)Se6 octahedra, edges with three equivalent Pm(2)Se6 octahedra, and edges with four equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 4-6°. There are two inequivalent Pm sites. In the first Pm site, Pm(1) is bonded to one Se(3), two equivalent Se(4), and three equivalent Se(2) atoms to form PmSe6 octahedra that share corners with three equivalent Pm(2)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Pm(2)Se6 octahedra, edges with four equivalent Pm(1)Se6 octahedra, and  an edgeedge with one Mg(1)Se5 square pyramid. The corner-sharing octahedral tilt angles range from 53-59°. In the second Pm site, Pm(2) is bonded to one Se(2), one Se(4), two equivalent Se(1), and two equivalent Se(3) atoms to form PmSe6 octahedra that share corners with three equivalent Pm(1)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Pm(1)Se6 octahedra, edges with two equivalent Pm(2)Se6 octahedra, and edges with three equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 53-59°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Mg(1) and two equivalent Pm(2) atoms to form SePm2Mg3 square pyramids that share corners with two equivalent Se(4)Pm3Mg2 square pyramids, edges with three equivalent Se(4)Pm3Mg2 square pyramids, and edges with four equivalent Se(1)Pm2Mg3 square pyramids. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Pm(2) and three equivalent Pm(1) atoms. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Pm(1) and two equivalent Pm(2) atoms. In the fourth Se site, Se(4) is bonded to two equivalent Mg(1), one Pm(2), and two equivalent Pm(1) atoms to form SePm3Mg2 square pyramids that share corners with two equivalent Se(1)Pm2Mg3 square pyramids, edges with two equivalent Se(4)Pm3Mg2 square pyramids, and edges with three equivalent Se(1)Pm2Mg3 square pyramids. is represented by the Crystallographic Information File (CIF) [CIF]
data_Pm2MgSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.402
_cell_length_b   4.109
_cell_length_c   14.527
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   800.051
_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
  Pm  Pm0  1  0.118  0.250  0.073  1.0
  Pm  Pm1  1  0.882  0.750  0.927  1.0
  Pm  Pm2  1  0.382  0.750  0.573  1.0
  Pm  Pm3  1  0.618  0.250  0.427  1.0
  Pm  Pm4  1  0.138  0.250  0.704  1.0
  Pm  Pm5  1  0.862  0.750  0.296  1.0
  Pm  Pm6  1  0.362  0.750  0.204  1.0
  Pm  Pm7  1  0.638  0.250  0.796  1.0
  Mg  Mg8  1  0.108  0.750  0.460  1.0
  Mg  Mg9  1  0.892  0.250  0.540  1.0
  Mg  Mg10  1  0.392  0.250  0.960  1.0
  Mg  Mg11  1  0.608  0.750  0.040  1.0
  Se  Se12  1  0.002  0.750  0.616  1.0
  Se  Se13  1  0.998  0.250  0.384  1.0
  Se  Se14  1  0.498  0.250  0.116  1.0
  Se  Se15  1  0.502  0.750  0.884  1.0
  Se  Se16  1  0.028  0.250  0.883  1.0
  Se  Se17  1  0.972  0.750  0.117  1.0
  Se  Se18  1  0.472  0.750  0.383  1.0
  Se  Se19  1  0.528  0.250  0.617  1.0
  Se  Se20  1  0.224  0.250  0.247  1.0
  Se  Se21  1  0.776  0.750  0.753  1.0
  Se  Se22  1  0.276  0.750  0.747  1.0
  Se  Se23  1  0.724  0.250  0.253  1.0
  Se  Se24  1  0.265  0.750  0.014  1.0
  Se  Se25  1  0.735  0.250  0.986  1.0
  Se  Se26  1  0.235  0.250  0.514  1.0
  Se  Se27  1  0.765  0.750  0.486  1.0
[/CIF]
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The compound described by MgPm2Se4 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 Pm(1)Se6 octahedra, corners with two equivalent Pm(2)Se6 octahedra,  an edgeedge with one Pm(1)Se6 octahedra, edges with three equivalent Pm(2)Se6 octahedra, and edges with four equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 4-6°. There are two inequivalent Pm sites. In the first Pm site, Pm(1) is bonded to one Se(3), two equivalent Se(4), and three equivalent Se(2) atoms to form PmSe6 octahedra that share corners with three equivalent Pm(2)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Pm(2)Se6 octahedra, edges with four equivalent Pm(1)Se6 octahedra, and  an edgeedge with one Mg(1)Se5 square pyramid. The corner-sharing octahedral tilt angles range from 53-59°. In the second Pm site, Pm(2) is bonded to one Se(2), one Se(4), two equivalent Se(1), and two equivalent Se(3) atoms to form PmSe6 octahedra that share corners with three equivalent Pm(1)Se6 octahedra, corners with two equivalent Mg(1)Se5 square pyramids, edges with two equivalent Pm(1)Se6 octahedra, edges with two equivalent Pm(2)Se6 octahedra, and edges with three equivalent Mg(1)Se5 square pyramids. The corner-sharing octahedral tilt angles range from 53-59°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Mg(1) and two equivalent Pm(2) atoms to form SePm2Mg3 square pyramids that share corners with two equivalent Se(4)Pm3Mg2 square pyramids, edges with three equivalent Se(4)Pm3Mg2 square pyramids, and edges with four equivalent Se(1)Pm2Mg3 square pyramids. In the second Se site, Se(2) is bonded in a rectangular see-saw-like geometry to one Pm(2) and three equivalent Pm(1) atoms. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Pm(1) and two equivalent Pm(2) atoms. In the fourth Se site, Se(4) is bonded to two equivalent Mg(1), one Pm(2), and two equivalent Pm(1) atoms to form SePm3Mg2 square pyramids that share corners with two equivalent Se(1)Pm2Mg3 square pyramids, edges with two equivalent Se(4)Pm3Mg2 square pyramids, and edges with three equivalent Se(1)Pm2Mg3 square pyramids. is represented by the Crystallographic Information File (CIF) [CIF]
data_Pm2MgSe4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   13.402
_cell_length_b   4.109
_cell_length_c   14.527
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   90.000
_symmetry_Int_Tables_number   1
_cell_volume   800.051
_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
  Pm  Pm0  1  0.118  0.250  0.073  1.0
  Pm  Pm1  1  0.882  0.750  0.927  1.0
  Pm  Pm2  1  0.382  0.750  0.573  1.0
  Pm  Pm3  1  0.618  0.250  0.427  1.0
  Pm  Pm4  1  0.138  0.250  0.704  1.0
  Pm  Pm5  1  0.862  0.750  0.296  1.0
  Pm  Pm6  1  0.362  0.750  0.204  1.0
  Pm  Pm7  1  0.638  0.250  0.796  1.0
  Mg  Mg8  1  0.108  0.750  0.460  1.0
  Mg  Mg9  1  0.892  0.250  0.540  1.0
  Mg  Mg10  1  0.392  0.250  0.960  1.0
  Mg  Mg11  1  0.608  0.750  0.040  1.0
  Se  Se12  1  0.002  0.750  0.616  1.0
  Se  Se13  1  0.998  0.250  0.384  1.0
  Se  Se14  1  0.498  0.250  0.116  1.0
  Se  Se15  1  0.502  0.750  0.884  1.0
  Se  Se16  1  0.028  0.250  0.883  1.0
  Se  Se17  1  0.972  0.750  0.117  1.0
  Se  Se18  1  0.472  0.750  0.383  1.0
  Se  Se19  1  0.528  0.250  0.617  1.0
  Se  Se20  1  0.224  0.250  0.247  1.0
  Se  Se21  1  0.776  0.750  0.753  1.0
  Se  Se22  1  0.276  0.750  0.747  1.0
  Se  Se23  1  0.724  0.250  0.253  1.0
  Se  Se24  1  0.265  0.750  0.014  1.0
  Se  Se25  1  0.735  0.250  0.986  1.0
  Se  Se26  1  0.235  0.250  0.514  1.0
  Se  Se27  1  0.765  0.750  0.486  1.0
[/CIF]
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