data_CeMg2As
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.21
_cell_length_b   5.21
_cell_length_c   5.21
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   CeMg2As
_chemical_formula_sum   'Ce1 Mg2 As1'
_cell_volume   99.84
_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
  Ce  Ce1  1  0.68  0.68  0.68  1.0
  Mg  Mg2  1  0.52  0.52  0.52  1.0
  Mg  Mg3  1  0.84  0.84  0.84  1.0
  As  As0  1  0.0  0.0  0.0  1.0

data_CeMg2As
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.21
_cell_length_b   5.21
_cell_length_c   12.76
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   CeMg2As
_chemical_formula_sum   'Ce3 Mg6 As3'
_cell_volume   299.53
_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
  Ce  Ce0  3  0.0  0.0  0.32  1.0
  Mg  Mg1  3  0.0  0.0  0.16  1.0
  Mg  Mg2  3  0.0  0.0  0.48  1.0
  As  As3  3  0.0  0.0  0.0  1.0

Ce Mg Mg As
Ce Mg Mg As 0 1 o o o 0 2 o o o 2 3 + + + 
Mg2CeAs crystallizes in the trigonal R3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a single-bond geometry to one Ce(1) atom. The Mg(1)-Ce(1) bond length is 2.03 Å. In the second Mg site, Mg(2) is bonded in a linear geometry to one Ce(1) and one As(1) atom. The Mg(2)-Ce(1) bond length is 2.03 Å. The Mg(2)-As(1) bond length is 2.03 Å. Ce(1) is bonded to one Mg(1), one Mg(2), and three equivalent As(1) atoms to form CeMg2As3 trigonal bipyramids that share corners with six equivalent Ce(1)Mg2As3 trigonal bipyramids and  a cornercorner with one As(1)Ce3Mg trigonal pyramid. All Ce(1)-As(1) bond lengths are 3.01 Å. As(1) is bonded to one Mg(2) and three equivalent Ce(1) atoms to form distorted AsCe3Mg trigonal pyramids that share  a cornercorner with one Ce(1)Mg2As3 trigonal bipyramid and corners with six equivalent As(1)Ce3Mg trigonal pyramids.