The crystal structure described by Mg2Ca crystallizes in the orthorhombic Cmcm space group. Ca(1) is bonded to six equivalent Ca(1), two equivalent Mg(2), and four equivalent Mg(1) atoms to form distorted CaCa6Mg6 cuboctahedra that share corners with six equivalent Ca(1)Ca6Mg6 cuboctahedra, corners with six equivalent Mg(2)Ca2Mg10 cuboctahedra, corners with six equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with three equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with four equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with eleven equivalent Mg(2)Ca2Mg10 cuboctahedra, faces with four equivalent Mg(2)Ca2Mg10 cuboctahedra, faces with eight equivalent Ca(1)Ca6Mg6 cuboctahedra, and faces with eight equivalent Mg(1)Ca4Mg8 cuboctahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Ca(1), two equivalent Mg(1), and six equivalent Mg(2) atoms to form distorted MgCa4Mg8 cuboctahedra that share corners with six equivalent Ca(1)Ca6Mg6 cuboctahedra, corners with six equivalent Mg(2)Ca2Mg10 cuboctahedra, corners with six equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with three equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with seven equivalent Mg(2)Ca2Mg10 cuboctahedra, edges with eight equivalent Mg(1)Ca4Mg8 cuboctahedra, faces with six equivalent Mg(2)Ca2Mg10 cuboctahedra, faces with six equivalent Mg(1)Ca4Mg8 cuboctahedra, and faces with eight equivalent Ca(1)Ca6Mg6 cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Ca(1), four equivalent Mg(2), and six equivalent Mg(1) atoms to form distorted MgCa2Mg10 cuboctahedra that share corners with six equivalent Ca(1)Ca6Mg6 cuboctahedra, corners with six equivalent Mg(2)Ca2Mg10 cuboctahedra, corners with six equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with seven equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with eleven equivalent Ca(1)Ca6Mg6 cuboctahedra, faces with four equivalent Ca(1)Ca6Mg6 cuboctahedra, faces with six equivalent Mg(1)Ca4Mg8 cuboctahedra, and faces with ten equivalent Mg(2)Ca2Mg10 cuboctahedra. is represented by the CIF file [CIF]
data_CaMg2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.120
_cell_length_b   9.120
_cell_length_c   5.617
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   158.250
_symmetry_Int_Tables_number   1
_cell_volume   173.140
_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  0.286  0.714  0.250  1.0
  Ca  Ca1  1  0.714  0.286  0.750  1.0
  Mg  Mg2  1  0.605  0.395  0.250  1.0
  Mg  Mg3  1  0.953  0.047  0.250  1.0
  Mg  Mg4  1  0.047  0.953  0.750  1.0
  Mg  Mg5  1  0.395  0.605  0.750  1.0
[/CIF]
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The crystal structure described by Mg2Ca crystallizes in the orthorhombic Cmcm space group. Ca(1) is bonded to six equivalent Ca(1), two equivalent Mg(2), and four equivalent Mg(1) atoms to form distorted CaCa6Mg6 cuboctahedra that share corners with six equivalent Ca(1)Ca6Mg6 cuboctahedra, corners with six equivalent Mg(2)Ca2Mg10 cuboctahedra, corners with six equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with three equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with four equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with eleven equivalent Mg(2)Ca2Mg10 cuboctahedra, faces with four equivalent Mg(2)Ca2Mg10 cuboctahedra, faces with eight equivalent Ca(1)Ca6Mg6 cuboctahedra, and faces with eight equivalent Mg(1)Ca4Mg8 cuboctahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Ca(1), two equivalent Mg(1), and six equivalent Mg(2) atoms to form distorted MgCa4Mg8 cuboctahedra that share corners with six equivalent Ca(1)Ca6Mg6 cuboctahedra, corners with six equivalent Mg(2)Ca2Mg10 cuboctahedra, corners with six equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with three equivalent Ca(1)Ca6Mg6 cuboctahedra, edges with seven equivalent Mg(2)Ca2Mg10 cuboctahedra, edges with eight equivalent Mg(1)Ca4Mg8 cuboctahedra, faces with six equivalent Mg(2)Ca2Mg10 cuboctahedra, faces with six equivalent Mg(1)Ca4Mg8 cuboctahedra, and faces with eight equivalent Ca(1)Ca6Mg6 cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Ca(1), four equivalent Mg(2), and six equivalent Mg(1) atoms to form distorted MgCa2Mg10 cuboctahedra that share corners with six equivalent Ca(1)Ca6Mg6 cuboctahedra, corners with six equivalent Mg(2)Ca2Mg10 cuboctahedra, corners with six equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with seven equivalent Mg(1)Ca4Mg8 cuboctahedra, edges with eleven equivalent Ca(1)Ca6Mg6 cuboctahedra, faces with four equivalent Ca(1)Ca6Mg6 cuboctahedra, faces with six equivalent Mg(1)Ca4Mg8 cuboctahedra, and faces with ten equivalent Mg(2)Ca2Mg10 cuboctahedra. is represented by the CIF file [CIF]
data_CaMg2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   9.120
_cell_length_b   9.120
_cell_length_c   5.617
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   158.250
_symmetry_Int_Tables_number   1
_cell_volume   173.140
_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  0.286  0.714  0.250  1.0
  Ca  Ca1  1  0.714  0.286  0.750  1.0
  Mg  Mg2  1  0.605  0.395  0.250  1.0
  Mg  Mg3  1  0.953  0.047  0.250  1.0
  Mg  Mg4  1  0.047  0.953  0.750  1.0
  Mg  Mg5  1  0.395  0.605  0.750  1.0
[/CIF]
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