data_SrMgCr3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.21
_cell_length_b   5.21
_cell_length_c   5.21
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   SrMgCr3
_chemical_formula_sum   'Sr1 Mg1 Cr3'
_cell_volume   141.18
_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  Sr0  1  0.6  0.6  0.6  1.0
  Mg  Mg1  1  0.0  0.0  0.0  1.0
  Cr  Cr2  1  0.0  0.6  0.0  1.0
  Cr  Cr3  1  0.0  0.0  0.6  1.0
  Cr  Cr4  1  0.6  0.0  0.0  1.0

data_SrMgCr3
_symmetry_space_group_name_H-M   R3m
_cell_length_a   7.36
_cell_length_b   7.36
_cell_length_c   9.02
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   SrMgCr3
_chemical_formula_sum   'Sr3 Mg3 Cr9'
_cell_volume   423.55
_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  0.6  1.0
  Mg  Mg1  3  0.0  0.0  0.0  1.0
  Cr  Cr2  9  0.07  0.53  0.53  1.0

Sr Mg Cr Cr Cr
SrMgCr3 crystallizes in the trigonal R3m space group. Sr(1) is bonded in a 9-coordinate geometry to nine equivalent Cr(1) atoms. There are three shorter (2.92 Å) and six longer (3.76 Å) Sr(1)-Cr(1) bond lengths. Mg(1) is bonded to six equivalent Cr(1) atoms to form distorted corner-sharing MgCr6 octahedra. The corner-sharing octahedra are not tilted. There are three shorter (2.06 Å) and three longer (3.14 Å) Mg(1)-Cr(1) bond lengths. Cr(1) is bonded in a 1-coordinate geometry to three equivalent Sr(1) and two equivalent Mg(1) atoms.