data_CaMg2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.35
_cell_length_b   5.35
_cell_length_c   5.35
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   CaMg2
_chemical_formula_sum   'Ca1 Mg2'
_cell_volume   108.54
_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
  Ca  Ca0  1  0.0  0.0  0.0  1.0
  Mg  Mg1  1  0.68  0.68  0.68  1.0
  Mg  Mg2  1  0.89  0.89  0.89  1.0

data_CaMg2
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.35
_cell_length_b   5.35
_cell_length_c   13.12
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   CaMg2
_chemical_formula_sum   'Ca3 Mg6'
_cell_volume   325.63
_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
  Ca  Ca0  3  0.0  0.0  0.0  1.0
  Mg  Mg1  3  0.0  0.0  0.11  1.0
  Mg  Mg2  3  0.0  0.0  0.32  1.0

Ca Mg Mg
Mg2Ca crystallizes in the trigonal R3m space group. Ca(1) is bonded in a single-bond geometry to one Mg(2) and three equivalent Mg(1) atoms. The Ca(1)-Mg(2) bond length is 1.40 Å. All Ca(1)-Mg(1) bond lengths are 3.10 Å. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Ca(1) and one Mg(2) atom to form distorted corner-sharing MgCa3Mg trigonal pyramids. The Mg(1)-Mg(2) bond length is 2.81 Å. In the second Mg site, Mg(2) is bonded in a single-bond geometry to one Ca(1) and one Mg(1) atom.