The structure described by K3Cu3Nb2Se8 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. Nb(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted NbSe4 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 Nb(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 Nb(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 Nb(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 Nb(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 Nb(1), and one Cu(2) atom to form a mixture of distorted edge and corner-sharing SeK4NbCu 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 Nb(1), and one Cu(2) atom. is represented by the CIF card [CIF]
data_K3Nb2Cu3Se8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.717
_cell_length_b   12.568
_cell_length_c   13.927
_cell_angle_alpha   68.863
_cell_angle_beta   78.156
_cell_angle_gamma   76.854
_symmetry_Int_Tables_number   1
_cell_volume   900.498
_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  0.731  0.710  0.905  1.0
  K  K1  1  0.346  0.790  0.595  1.0
  K  K2  1  0.269  0.290  0.095  1.0
  K  K3  1  0.654  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
  Nb  Nb6  1  0.156  0.471  0.779  1.0
  Nb  Nb7  1  0.406  0.029  0.721  1.0
  Nb  Nb8  1  0.844  0.529  0.221  1.0
  Nb  Nb9  1  0.594  0.971  0.279  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  0.903  0.034  0.721  1.0
  Cu  Cu13  1  0.658  0.466  0.779  1.0
  Cu  Cu14  1  0.097  0.966  0.279  1.0
  Cu  Cu15  1  0.342  0.534  0.221  1.0
  Se  Se16  1  0.948  0.306  0.875  1.0
  Se  Se17  1  0.129  0.194  0.625  1.0
  Se  Se18  1  0.052  0.694  0.125  1.0
  Se  Se19  1  0.871  0.806  0.375  1.0
  Se  Se20  1  0.489  0.413  0.657  1.0
  Se  Se21  1  0.559  0.087  0.843  1.0
  Se  Se22  1  0.511  0.587  0.343  1.0
  Se  Se23  1  0.441  0.913  0.157  1.0
  Se  Se24  1  0.870  0.630  0.684  1.0
  Se  Se25  1  0.184  0.870  0.816  1.0
  Se  Se26  1  0.130  0.370  0.316  1.0
  Se  Se27  1  0.816  0.130  0.184  1.0
  Se  Se28  1  0.744  0.969  0.607  1.0
  Se  Se29  1  0.319  0.531  0.893  1.0
  Se  Se30  1  0.256  0.031  0.393  1.0
  Se  Se31  1  0.681  0.469  0.107  1.0
[/CIF]
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The structure described by K3Cu3Nb2Se8 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. Nb(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form distorted NbSe4 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 Nb(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 Nb(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 Nb(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 Nb(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 Nb(1), and one Cu(2) atom to form a mixture of distorted edge and corner-sharing SeK4NbCu 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 Nb(1), and one Cu(2) atom. is represented by the CIF card [CIF]
data_K3Nb2Cu3Se8
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.717
_cell_length_b   12.568
_cell_length_c   13.927
_cell_angle_alpha   68.863
_cell_angle_beta   78.156
_cell_angle_gamma   76.854
_symmetry_Int_Tables_number   1
_cell_volume   900.498
_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  0.731  0.710  0.905  1.0
  K  K1  1  0.346  0.790  0.595  1.0
  K  K2  1  0.269  0.290  0.095  1.0
  K  K3  1  0.654  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
  Nb  Nb6  1  0.156  0.471  0.779  1.0
  Nb  Nb7  1  0.406  0.029  0.721  1.0
  Nb  Nb8  1  0.844  0.529  0.221  1.0
  Nb  Nb9  1  0.594  0.971  0.279  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  0.903  0.034  0.721  1.0
  Cu  Cu13  1  0.658  0.466  0.779  1.0
  Cu  Cu14  1  0.097  0.966  0.279  1.0
  Cu  Cu15  1  0.342  0.534  0.221  1.0
  Se  Se16  1  0.948  0.306  0.875  1.0
  Se  Se17  1  0.129  0.194  0.625  1.0
  Se  Se18  1  0.052  0.694  0.125  1.0
  Se  Se19  1  0.871  0.806  0.375  1.0
  Se  Se20  1  0.489  0.413  0.657  1.0
  Se  Se21  1  0.559  0.087  0.843  1.0
  Se  Se22  1  0.511  0.587  0.343  1.0
  Se  Se23  1  0.441  0.913  0.157  1.0
  Se  Se24  1  0.870  0.630  0.684  1.0
  Se  Se25  1  0.184  0.870  0.816  1.0
  Se  Se26  1  0.130  0.370  0.316  1.0
  Se  Se27  1  0.816  0.130  0.184  1.0
  Se  Se28  1  0.744  0.969  0.607  1.0
  Se  Se29  1  0.319  0.531  0.893  1.0
  Se  Se30  1  0.256  0.031  0.393  1.0
  Se  Se31  1  0.681  0.469  0.107  1.0
[/CIF]
.