data_TaNbSe2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   3.23
_cell_length_b   3.23
_cell_length_c   6.46
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   1
_chemical_formula_structural   TaNbSe2
_chemical_formula_sum   'Ta1 Nb1 Se2'
_cell_volume   67.48
_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
  Ta  Ta3  1  0.0  0.0  0.23  1.0
  Nb  Nb0  1  0.0  0.0  0.0  1.0
  Se  Se1  1  0.62  0.62  0.62  1.0
  Se  Se2  1  0.62  0.62  0.84  1.0

data_TaNbSe2
_symmetry_space_group_name_H-M   Cm
_cell_length_a   4.57
_cell_length_b   4.57
_cell_length_c   6.46
_cell_angle_alpha   90.0
_cell_angle_beta   90.0
_cell_angle_gamma   90.0
_symmetry_Int_Tables_number   8
_chemical_formula_structural   TaNbSe2
_chemical_formula_sum   'Ta2 Nb2 Se4'
_cell_volume   134.97
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
  2  'x, -y, z'
  3  'x+1/2, y+1/2, z'
  4  'x+1/2, -y+1/2, 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
  Ta  Ta0  2  0.0  0.0  0.23  1.0
  Nb  Nb1  2  0.0  0.0  0.0  1.0
  Se  Se2  2  0.12  0.5  0.62  1.0
  Se  Se3  2  0.12  0.5  0.84  1.0

Ta Nb Se Se
Ta Nb Se Se 0 1 o o o 2 3 o o o 
TaNbSe2 crystallizes in the monoclinic Cm space group. Ta(1) is bonded in a distorted single-bond geometry to one Nb(1) and three equivalent Se(1) atoms. The Ta(1)-Nb(1) bond length is 1.49 Å. There is one shorter (3.05 Å) and two longer (3.43 Å) Ta(1)-Se(1) bond lengths. Nb(1) is bonded in a 5-coordinate geometry to one Ta(1) and four equivalent Se(2) atoms. There are a spread of Nb(1)-Se(2) bond distances ranging from 2.03-2.99 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to three equivalent Ta(1) and one Se(2) atom. The Se(1)-Se(2) bond length is 1.47 Å. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to four equivalent Nb(1) and one Se(1) atom.