data_Sr2Mg
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.92
_cell_length_b   5.92
_cell_length_c   5.92
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Sr2Mg
_chemical_formula_sum   'Sr2 Mg1'
_cell_volume   146.46
_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
  Sr  Sr1  1  0.28  0.28  0.28  1.0
  Sr  Sr2  1  0.09  0.09  0.09  1.0
  Mg  Mg0  1  0.0  0.0  0.0  1.0

data_Sr2Mg
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.92
_cell_length_b   5.92
_cell_length_c   14.49
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   Sr2Mg
_chemical_formula_sum   'Sr6 Mg3'
_cell_volume   439.38
_cell_formula_units_Z   3
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  '-y, x-y, z'
  3  '-x+y, -x, z'
  4  '-y, -x, z'
  5  '-x+y, y, z'
  6  'x, x-y, z'
  7  'x+1/3, y+2/3, z+2/3'
  8  '-y+1/3, x-y+2/3, z+2/3'
  9  '-x+y+1/3, -x+2/3, z+2/3'
  10  '-y+1/3, -x+2/3, z+2/3'
  11  '-x+y+1/3, y+2/3, z+2/3'
  12  'x+1/3, x-y+2/3, z+2/3'
  13  'x+2/3, y+1/3, z+1/3'
  14  '-y+2/3, x-y+1/3, z+1/3'
  15  '-x+y+2/3, -x+1/3, z+1/3'
  16  '-y+2/3, -x+1/3, z+1/3'
  17  '-x+y+2/3, y+1/3, z+1/3'
  18  'x+2/3, x-y+1/3, z+1/3'
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
  Sr  Sr0  3  0.0  0.0  0.72  1.0
  Sr  Sr1  3  0.0  0.0  0.91  1.0
  Mg  Mg2  3  0.0  0.0  0.0  1.0

Sr Sr Mg
Sr Sr Mg 0 1 o o o 1 2 o o o 
Sr2Mg1 crystallizes in the trigonal R3m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one Sr(2) and three equivalent Mg(1) atoms to form corner-sharing SrSrMg3 tetrahedra. The Sr(1)-Sr(2) bond length is 2.66 Å. All Sr(1)-Mg(1) bond lengths are 3.52 Å. In the second Sr site, Sr(2) is bonded in a single-bond geometry to one Sr(1) and one Mg(1) atom. The Sr(2)-Mg(1) bond length is 1.33 Å. Mg(1) is bonded in a single-bond geometry to one Sr(2) and three equivalent Sr(1) atoms.