data_Cu2AgSe
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   4.5
_cell_length_b   4.5
_cell_length_c   4.5
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   Cu2AgSe
_chemical_formula_sum   'Cu2 Ag1 Se1'
_cell_volume   64.31
_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
  Cu  Cu1  1  0.59  0.59  0.59  1.0
  Cu  Cu2  1  0.0  0.0  0.0  1.0
  Ag  Ag0  1  0.77  0.77  0.77  1.0
  Se  Se3  1  0.18  0.18  0.18  1.0

data_Cu2AgSe
_symmetry_space_group_name_H-M   R3m
_cell_length_a   4.5
_cell_length_b   4.5
_cell_length_c   11.02
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   Cu2AgSe
_chemical_formula_sum   'Cu6 Ag3 Se3'
_cell_volume   192.93
_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
  Cu  Cu0  3  0.0  0.0  0.0  1.0
  Cu  Cu1  3  0.0  0.0  0.41  1.0
  Ag  Ag2  3  0.0  0.0  0.23  1.0
  Se  Se3  3  0.0  0.0  0.82  1.0

Cu Cu Ag Se
AgCu2Se crystallizes in the trigonal R3m space group. Ag(1) is bonded in a 5-coordinate geometry to one Cu(1), one Cu(2), and three equivalent Se(1) atoms. The Ag(1)-Cu(1) bond length is 1.98 Å. The Ag(1)-Cu(2) bond length is 2.54 Å. All Ag(1)-Se(1) bond lengths are 2.73 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Ag(1) and three equivalent Se(1) atoms to form distorted corner-sharing CuAgSe3 tetrahedra. All Cu(1)-Se(1) bond lengths are 2.73 Å. In the second Cu site, Cu(2) is bonded in a single-bond geometry to one Ag(1) and one Se(1) atom. The Cu(2)-Se(1) bond length is 1.98 Å. Se(1) is bonded in a distorted single-bond geometry to three equivalent Ag(1), one Cu(2), and three equivalent Cu(1) atoms.