data_CaMg3
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.07
_cell_length_b   6.07
_cell_length_c   6.07
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   CaMg3
_chemical_formula_sum   'Ca2 Mg6'
_cell_volume   223.36
_cell_formula_units_Z   2
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
  Ca  Ca0  1  0.03  0.03  0.03  1.0
  Ca  Ca1  1  0.0  0.0  0.0  1.0
  Mg  Mg2  1  0.03  0.55  0.0  1.0
  Mg  Mg3  1  0.03  0.52  0.0  1.0
  Mg  Mg4  1  0.55  0.0  0.03  1.0
  Mg  Mg5  1  0.0  0.03  0.55  1.0
  Mg  Mg6  1  0.0  0.03  0.52  1.0
  Mg  Mg7  1  0.52  0.0  0.03  1.0

data_CaMg3
_symmetry_space_group_name_H-M   R3
_cell_length_a   8.58
_cell_length_b   8.58
_cell_length_c   10.51
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   146
_chemical_formula_structural   CaMg3
_chemical_formula_sum   'Ca6 Mg18'
_cell_volume   670.07
_cell_formula_units_Z   6
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
  Ca  Ca0  3  0.0  0.0  0.0  1.0
  Ca  Ca1  3  0.0  0.0  0.03  1.0
  Mg  Mg2  9  0.0  0.48  0.52  1.0
  Mg  Mg3  9  0.02  0.49  0.53  1.0

Ca Ca Mg Mg Mg Mg Mg Mg
Mg3Ca crystallizes in the trigonal R3 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a distorted single-bond geometry to one Ca(2) and three equivalent Mg(2) atoms. The Ca(1)-Ca(2) bond length is 0.35 Å. All Ca(1)-Mg(2) bond lengths are 2.94 Å. In the second Ca site, Ca(2) is bonded in a distorted single-bond geometry to one Ca(1) and three equivalent Mg(1) atoms. All Ca(2)-Mg(1) bond lengths are 2.73 Å. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a linear geometry to one Ca(2) and one Mg(2) atom. The Mg(1)-Mg(2) bond length is 0.20 Å. In the second Mg site, Mg(2) is bonded in a linear geometry to one Ca(1) and one Mg(1) atom.