data_SrMg2Cu
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.2
_cell_length_b   5.2
_cell_length_c   5.2
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   SrMg2Cu
_chemical_formula_sum   'Sr1 Mg2 Cu1'
_cell_volume   99.31
_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
  Sr  Sr3  1  0.84  0.84  0.84  1.0
  Mg  Mg1  1  0.0  0.0  0.0  1.0
  Mg  Mg2  1  0.51  0.51  0.51  1.0
  Cu  Cu0  1  0.68  0.68  0.68  1.0

data_SrMg2Cu
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.2
_cell_length_b   5.2
_cell_length_c   12.73
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   SrMg2Cu
_chemical_formula_sum   'Sr3 Mg6 Cu3'
_cell_volume   297.92
_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
  Sr  Sr0  3  0.0  0.0  0.16  1.0
  Mg  Mg1  3  0.0  0.0  0.0  1.0
  Mg  Mg2  3  0.0  0.0  0.49  1.0
  Cu  Cu3  3  0.0  0.0  0.32  1.0

Sr Mg Mg Cu
Sr Mg Mg Cu 0 3 o o o 0 1 + + + 2 3 o o o 
SrMg2Cu crystallizes in the trigonal R3m space group. Sr(1) is bonded in a 2-coordinate geometry to one Mg(1), three equivalent Mg(2), and one Cu(1) atom. The Sr(1)-Mg(1) bond length is 2.07 Å. All Sr(1)-Mg(2) bond lengths are 3.00 Å. The Sr(1)-Cu(1) bond length is 2.07 Å. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Sr(1) and three equivalent Cu(1) atoms to form distorted MgSrCu3 trigonal pyramids that share  a cornercorner with one Cu(1)SrMg4 trigonal bipyramid and corners with six equivalent Mg(1)SrCu3 trigonal pyramids. All Mg(1)-Cu(1) bond lengths are 3.00 Å. In the second Mg site, Mg(2) is bonded in a distorted single-bond geometry to three equivalent Sr(1) and one Cu(1) atom. The Mg(2)-Cu(1) bond length is 2.07 Å. Cu(1) is bonded to one Sr(1), one Mg(2), and three equivalent Mg(1) atoms to form distorted CuSrMg4 trigonal bipyramids that share corners with six equivalent Cu(1)SrMg4 trigonal bipyramids and  a cornercorner with one Mg(1)SrCu3 trigonal pyramid.