data_HgSeBr2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.19
_cell_length_b   5.19
_cell_length_c   5.19
_cell_angle_alpha   60.0
_cell_angle_beta   60.0
_cell_angle_gamma   60.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   HgSeBr2
_chemical_formula_sum   'Hg1 Se1 Br2'
_cell_volume   98.92
_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
  Hg  Hg2  1  0.84  0.84  0.84  1.0
  Se  Se3  1  0.0  0.0  0.0  1.0
  Br  Br0  1  0.51  0.51  0.51  1.0
  Br  Br1  1  0.67  0.67  0.67  1.0

data_HgSeBr2
_symmetry_space_group_name_H-M   R3m
_cell_length_a   5.19
_cell_length_b   5.19
_cell_length_c   12.72
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   120.0
_symmetry_Int_Tables_number   160
_chemical_formula_structural   HgSeBr2
_chemical_formula_sum   'Hg3 Se3 Br6'
_cell_volume   296.75
_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
  Hg  Hg0  3  0.0  0.0  0.16  1.0
  Se  Se1  3  0.0  0.0  0.0  1.0
  Br  Br2  3  0.0  0.0  0.33  1.0
  Br  Br3  3  0.0  0.0  0.49  1.0

Hg Se Br Br
HgSeBr2 crystallizes in the trigonal R3m space group. Hg(1) is bonded to one Se(1), one Br(2), and three equivalent Br(1) atoms to form distorted HgSeBr4 trigonal bipyramids that share corners with six equivalent Hg(1)SeBr4 trigonal bipyramids,  a cornercorner with one Br(1)Hg3Br trigonal pyramid, and corners with three equivalent Se(1)HgBr3 trigonal pyramids. The Hg(1)-Se(1) bond length is 2.09 Å. The Hg(1)-Br(2) bond length is 2.09 Å. All Hg(1)-Br(1) bond lengths are 3.00 Å. Se(1) is bonded to one Hg(1) and three equivalent Br(2) atoms to form distorted SeHgBr3 trigonal pyramids that share corners with three equivalent Hg(1)SeBr4 trigonal bipyramids, corners with six equivalent Se(1)HgBr3 trigonal pyramids, and edges with three equivalent Br(1)Hg3Br trigonal pyramids. All Se(1)-Br(2) bond lengths are 3.00 Å. There are two inequivalent Br sites. In the first Br site, Br(1) is bonded to three equivalent Hg(1) and one Br(2) atom to form BrHg3Br trigonal pyramids that share  a cornercorner with one Hg(1)SeBr4 trigonal bipyramid, corners with six equivalent Br(1)Hg3Br trigonal pyramids, and edges with three equivalent Se(1)HgBr3 trigonal pyramids. The Br(1)-Br(2) bond length is 2.09 Å. In the second Br site, Br(2) is bonded in a distorted single-bond geometry to one Hg(1), three equivalent Se(1), and one Br(1) atom.