data_Mg2Be2Se
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.25
_cell_length_b   6.25
_cell_length_c   6.25
_cell_angle_alpha   143.2
_cell_angle_beta   143.2
_cell_angle_gamma   53.02
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Mg2Be2Se
_chemical_formula_sum   'Mg2 Be2 Se1'
_cell_volume   87.22
_cell_formula_units_Z   1
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
  Mg  Mg2  1  0.0  0.97  0.8  1.0
  Mg  Mg3  1  0.97  0.0  0.8  1.0
  Be  Be0  1  0.0  0.0  0.61  1.0
  Be  Be1  1  0.0  0.0  0.58  1.0
  Se  Se4  1  0.0  0.0  0.0  1.0

data_Mg2Be2Se
_symmetry_space_group_name_H-M   Cm
_cell_length_a   5.58
_cell_length_b   5.58
_cell_length_c   6.25
_cell_angle_alpha   90.0
_cell_angle_beta   116.51
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   Mg2Be2Se
_chemical_formula_sum   'Mg4 Be4 Se2'
_cell_volume   174.44
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  'x, -y, z'
  3  'x+1/2, y+1/2, z'
  4  'x+1/2, -y+1/2, 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
  Mg  Mg0  4  0.31  0.49  0.82  1.0
  Be  Be1  2  0.08  0.5  0.58  1.0
  Be  Be2  2  0.11  0.5  0.61  1.0
  Se  Se3  2  0.0  0.0  0.0  1.0

Mg Mg Be Be Se
Mg2Be2Se is Indium-like structured and crystallizes in the monoclinic Cm space group. The structure is zero-dimensional and consists of two Mg2Be2Se clusters. Mg(1) is bonded in a distorted single-bond geometry to one Mg(1), one Be(1), and one Se(1) atom. The Mg(1)-Mg(1) bond length is 0.15 Å. The Mg(1)-Be(1) bond length is 1.31 Å. The Mg(1)-Se(1) bond length is 1.14 Å. There are two inequivalent Be sites. In the first Be site, Be(1) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one Be(2) atom. The Be(1)-Be(2) bond length is 0.17 Å. In the second Be site, Be(2) is bonded in a single-bond geometry to one Be(1) atom. Se(1) is bonded in a 2-coordinate geometry to two equivalent Mg(1) atoms.