data_MgCr
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.4
_cell_length_b   5.4
_cell_length_c   5.4
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   MgCr
_chemical_formula_sum   'Mg4 Cr4'
_cell_volume   157.2
_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
  Mg  Mg4  1  0.18  0.88  0.22  1.0
  Mg  Mg5  1  0.52  0.52  0.52  1.0
  Mg  Mg6  1  0.22  0.18  0.88  1.0
  Mg  Mg7  1  0.88  0.22  0.18  1.0
  Cr  Cr0  1  0.55  0.24  0.85  1.0
  Cr  Cr1  1  0.15  0.15  0.15  1.0
  Cr  Cr2  1  0.85  0.55  0.24  1.0
  Cr  Cr3  1  0.24  0.85  0.55  1.0

data_MgCr
_symmetry_space_group_name_H-M   R3
_cell_length_a   7.63
_cell_length_b   7.63
_cell_length_c   9.35
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   146
_chemical_formula_structural   MgCr
_chemical_formula_sum   'Mg12 Cr12'
_cell_volume   471.6
_cell_formula_units_Z   12
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  'x+1/3, y+2/3, z+2/3'
  5  '-y+1/3, x-y+2/3, z+2/3'
  6  '-x+y+1/3, -x+2/3, z+2/3'
  7  'x+2/3, y+1/3, z+1/3'
  8  '-y+2/3, x-y+1/3, z+1/3'
  9  '-x+y+2/3, -x+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
  Mg  Mg0  9  0.09  0.87  0.09  1.0
  Mg  Mg1  3  0.0  0.0  0.52  1.0
  Cr  Cr2  9  0.03  0.67  0.21  1.0
  Cr  Cr3  3  0.0  0.0  0.15  1.0

Mg Mg Mg Mg Cr Cr Cr Cr
MgCr crystallizes in the trigonal R3 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 3-coordinate geometry to one Cr(2) and two equivalent Cr(1) atoms. The Mg(1)-Cr(2) bond length is 1.54 Å. There is one shorter (1.80 Å) and one longer (2.51 Å) Mg(1)-Cr(1) bond length. In the second Mg site, Mg(2) is bonded in a distorted trigonal planar geometry to three equivalent Cr(1) atoms. All Mg(2)-Cr(1) bond lengths are 2.33 Å. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded in a 3-coordinate geometry to one Mg(2) and two equivalent Mg(1) atoms. In the second Cr site, Cr(2) is bonded in a trigonal non-coplanar geometry to three equivalent Mg(1) atoms.