The material described by Mg2Ca is Bergman Structure: Mg32(Al,Zn)49 Bergman-derived structured and crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to three equivalent Ca(1), four equivalent Mg(2), and five equivalent Mg(1) atoms to form distorted CaCa3Mg9 cuboctahedra that share corners with six equivalent Ca(1)Ca3Mg9 cuboctahedra, corners with six equivalent Mg(1)Ca5Mg7 cuboctahedra, edges with four equivalent Ca(1)Ca3Mg9 cuboctahedra, edges with five equivalent Mg(1)Ca5Mg7 cuboctahedra, faces with six equivalent Ca(1)Ca3Mg9 cuboctahedra, and faces with eight equivalent Mg(1)Ca5Mg7 cuboctahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to five equivalent Ca(1), three equivalent Mg(2), and four equivalent Mg(1) atoms to form distorted MgCa5Mg7 cuboctahedra that share corners with six equivalent Ca(1)Ca3Mg9 cuboctahedra, corners with six equivalent Mg(1)Ca5Mg7 cuboctahedra, edges with five equivalent Ca(1)Ca3Mg9 cuboctahedra, edges with six equivalent Mg(1)Ca5Mg7 cuboctahedra, faces with five equivalent Mg(1)Ca5Mg7 cuboctahedra, and faces with eight equivalent Ca(1)Ca3Mg9 cuboctahedra. In the second Mg site, Mg(2) is bonded in a 11-coordinate geometry to four equivalent Ca(1), three equivalent Mg(1), and four equivalent Mg(2) atoms. is represented by the CIF card [CIF]
data_CaMg2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.792
_cell_length_b   6.792
_cell_length_c   7.690
_cell_angle_alpha   74.858
_cell_angle_beta   74.858
_cell_angle_gamma   29.724
_symmetry_Int_Tables_number   1
_cell_volume   169.345
_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  0.522  0.522  0.220  1.0
  Ca  Ca1  1  0.478  0.478  0.780  1.0
  Mg  Mg2  1  0.801  0.801  0.136  1.0
  Mg  Mg3  1  0.160  0.160  0.462  1.0
  Mg  Mg4  1  0.840  0.840  0.538  1.0
  Mg  Mg5  1  0.199  0.199  0.864  1.0
[/CIF]
.
The material described by Mg2Ca is Bergman Structure: Mg32(Al,Zn)49 Bergman-derived structured and crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to three equivalent Ca(1), four equivalent Mg(2), and five equivalent Mg(1) atoms to form distorted CaCa3Mg9 cuboctahedra that share corners with six equivalent Ca(1)Ca3Mg9 cuboctahedra, corners with six equivalent Mg(1)Ca5Mg7 cuboctahedra, edges with four equivalent Ca(1)Ca3Mg9 cuboctahedra, edges with five equivalent Mg(1)Ca5Mg7 cuboctahedra, faces with six equivalent Ca(1)Ca3Mg9 cuboctahedra, and faces with eight equivalent Mg(1)Ca5Mg7 cuboctahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to five equivalent Ca(1), three equivalent Mg(2), and four equivalent Mg(1) atoms to form distorted MgCa5Mg7 cuboctahedra that share corners with six equivalent Ca(1)Ca3Mg9 cuboctahedra, corners with six equivalent Mg(1)Ca5Mg7 cuboctahedra, edges with five equivalent Ca(1)Ca3Mg9 cuboctahedra, edges with six equivalent Mg(1)Ca5Mg7 cuboctahedra, faces with five equivalent Mg(1)Ca5Mg7 cuboctahedra, and faces with eight equivalent Ca(1)Ca3Mg9 cuboctahedra. In the second Mg site, Mg(2) is bonded in a 11-coordinate geometry to four equivalent Ca(1), three equivalent Mg(1), and four equivalent Mg(2) atoms. is represented by the CIF card [CIF]
data_CaMg2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   6.792
_cell_length_b   6.792
_cell_length_c   7.690
_cell_angle_alpha   74.858
_cell_angle_beta   74.858
_cell_angle_gamma   29.724
_symmetry_Int_Tables_number   1
_cell_volume   169.345
_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  0.522  0.522  0.220  1.0
  Ca  Ca1  1  0.478  0.478  0.780  1.0
  Mg  Mg2  1  0.801  0.801  0.136  1.0
  Mg  Mg3  1  0.160  0.160  0.462  1.0
  Mg  Mg4  1  0.840  0.840  0.538  1.0
  Mg  Mg5  1  0.199  0.199  0.864  1.0
[/CIF]
.