The structure described by K3Cu3Ta2Se8 crystallizes in the monoclinic C2/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one Se(1), three equivalent Se(3), and three equivalent Se(4) atoms. In the second K site, K(2) is bonded in a body-centered cubic geometry to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms. Ta(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted TaSe4 tetrahedra that share  an edgeedge with one Cu(1)Se4 tetrahedra and edges with two equivalent Cu(2)Se4 tetrahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with four equivalent Cu(2)Se4 tetrahedra and edges with two equivalent Ta(1)Se4 tetrahedra. In the second Cu site, Cu(2) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra and edges with two equivalent Ta(1)Se4 tetrahedra. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Ta(1), one Cu(1), and one Cu(2) atom. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent K(2), one Ta(1), one Cu(1), and one Cu(2) atom. In the third Se site, Se(3) is bonded to one K(2), three equivalent K(1), one Ta(1), and one Cu(2) atom to form a mixture of distorted corner and edge-sharing SeK4TaCu octahedra. The corner-sharing octahedral tilt angles range from 0-68°. In the fourth Se site, Se(4) is bonded in a 5-coordinate geometry to three equivalent K(1), one Ta(1), and one Cu(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_K3Ta2Cu3Se8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.708
_cell_length_b   12.576
_cell_length_c   13.941
_cell_angle_alpha   68.740
_cell_angle_beta   78.186
_cell_angle_gamma   76.882
_symmetry_Int_Tables_number   1
_cell_volume   900.060
_cell_formula_units_Z   2
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
  K  K0  1  0.733  0.710  0.905  1.0
  K  K1  1  0.348  0.790  0.595  1.0
  K  K2  1  0.267  0.290  0.095  1.0
  K  K3  1  0.652  0.210  0.405  1.0
  K  K4  1  0.000  0.500  0.500  1.0
  K  K5  1  0.000  0.000  0.000  1.0
  Ta  Ta6  1  0.158  0.470  0.778  1.0
  Ta  Ta7  1  0.407  0.030  0.722  1.0
  Ta  Ta8  1  0.842  0.530  0.222  1.0
  Ta  Ta9  1  0.593  0.970  0.278  1.0
  Cu  Cu10  1  0.276  0.250  0.750  1.0
  Cu  Cu11  1  0.724  0.750  0.250  1.0
  Cu  Cu12  1  0.904  0.034  0.721  1.0
  Cu  Cu13  1  0.659  0.466  0.779  1.0
  Cu  Cu14  1  0.096  0.966  0.279  1.0
  Cu  Cu15  1  0.341  0.534  0.221  1.0
  Se  Se16  1  0.950  0.307  0.875  1.0
  Se  Se17  1  0.132  0.193  0.625  1.0
  Se  Se18  1  0.050  0.693  0.125  1.0
  Se  Se19  1  0.868  0.807  0.375  1.0
  Se  Se20  1  0.488  0.414  0.656  1.0
  Se  Se21  1  0.559  0.086  0.844  1.0
  Se  Se22  1  0.512  0.586  0.344  1.0
  Se  Se23  1  0.441  0.914  0.156  1.0
  Se  Se24  1  0.875  0.629  0.684  1.0
  Se  Se25  1  0.188  0.871  0.816  1.0
  Se  Se26  1  0.125  0.371  0.316  1.0
  Se  Se27  1  0.812  0.129  0.184  1.0
  Se  Se28  1  0.741  0.969  0.607  1.0
  Se  Se29  1  0.317  0.531  0.893  1.0
  Se  Se30  1  0.259  0.031  0.393  1.0
  Se  Se31  1  0.683  0.469  0.107  1.0
[/CIF]
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The structure described by K3Cu3Ta2Se8 crystallizes in the monoclinic C2/c space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one Se(1), three equivalent Se(3), and three equivalent Se(4) atoms. In the second K site, K(2) is bonded in a body-centered cubic geometry to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms. Ta(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted TaSe4 tetrahedra that share  an edgeedge with one Cu(1)Se4 tetrahedra and edges with two equivalent Cu(2)Se4 tetrahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with four equivalent Cu(2)Se4 tetrahedra and edges with two equivalent Ta(1)Se4 tetrahedra. In the second Cu site, Cu(2) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted CuSe4 tetrahedra that share corners with two equivalent Cu(1)Se4 tetrahedra and edges with two equivalent Ta(1)Se4 tetrahedra. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Ta(1), one Cu(1), and one Cu(2) atom. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to two equivalent K(2), one Ta(1), one Cu(1), and one Cu(2) atom. In the third Se site, Se(3) is bonded to one K(2), three equivalent K(1), one Ta(1), and one Cu(2) atom to form a mixture of distorted corner and edge-sharing SeK4TaCu octahedra. The corner-sharing octahedral tilt angles range from 0-68°. In the fourth Se site, Se(4) is bonded in a 5-coordinate geometry to three equivalent K(1), one Ta(1), and one Cu(2) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_K3Ta2Cu3Se8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.708
_cell_length_b   12.576
_cell_length_c   13.941
_cell_angle_alpha   68.740
_cell_angle_beta   78.186
_cell_angle_gamma   76.882
_symmetry_Int_Tables_number   1
_cell_volume   900.060
_cell_formula_units_Z   2
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
  K  K0  1  0.733  0.710  0.905  1.0
  K  K1  1  0.348  0.790  0.595  1.0
  K  K2  1  0.267  0.290  0.095  1.0
  K  K3  1  0.652  0.210  0.405  1.0
  K  K4  1  0.000  0.500  0.500  1.0
  K  K5  1  0.000  0.000  0.000  1.0
  Ta  Ta6  1  0.158  0.470  0.778  1.0
  Ta  Ta7  1  0.407  0.030  0.722  1.0
  Ta  Ta8  1  0.842  0.530  0.222  1.0
  Ta  Ta9  1  0.593  0.970  0.278  1.0
  Cu  Cu10  1  0.276  0.250  0.750  1.0
  Cu  Cu11  1  0.724  0.750  0.250  1.0
  Cu  Cu12  1  0.904  0.034  0.721  1.0
  Cu  Cu13  1  0.659  0.466  0.779  1.0
  Cu  Cu14  1  0.096  0.966  0.279  1.0
  Cu  Cu15  1  0.341  0.534  0.221  1.0
  Se  Se16  1  0.950  0.307  0.875  1.0
  Se  Se17  1  0.132  0.193  0.625  1.0
  Se  Se18  1  0.050  0.693  0.125  1.0
  Se  Se19  1  0.868  0.807  0.375  1.0
  Se  Se20  1  0.488  0.414  0.656  1.0
  Se  Se21  1  0.559  0.086  0.844  1.0
  Se  Se22  1  0.512  0.586  0.344  1.0
  Se  Se23  1  0.441  0.914  0.156  1.0
  Se  Se24  1  0.875  0.629  0.684  1.0
  Se  Se25  1  0.188  0.871  0.816  1.0
  Se  Se26  1  0.125  0.371  0.316  1.0
  Se  Se27  1  0.812  0.129  0.184  1.0
  Se  Se28  1  0.741  0.969  0.607  1.0
  Se  Se29  1  0.317  0.531  0.893  1.0
  Se  Se30  1  0.259  0.031  0.393  1.0
  Se  Se31  1  0.683  0.469  0.107  1.0
[/CIF]
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