The crystal structure described by K2Fe2B2O7 crystallizes in the trigonal P321 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1) and three equivalent O(5) atoms to form corner-sharing FeO4 tetrahedra. In the second Fe site, Fe(2) is bonded to one O(2) and three equivalent O(4) atoms to form corner-sharing FeO4 tetrahedra. In the third Fe site, Fe(3) is bonded to one O(2) and three equivalent O(3) atoms to form corner-sharing FeO4 tetrahedra. B(1) is bonded in a trigonal planar geometry to one O(3), one O(4), and one O(5) atom. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Fe(1), and one B(1) atom. In the second O site, O(1) is bonded in a distorted linear geometry to three equivalent K(2) and two equivalent Fe(1) atoms. In the third O site, O(2) is bonded in a distorted linear geometry to three equivalent K(1), one Fe(2), and one Fe(3) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Fe(3), and one B(1) atom. In the fifth O site, O(4) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Fe(2), and one B(1) atom. is represented by the CIF file [CIF]
data_K2Fe2B2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.860
_cell_length_b   8.860
_cell_length_c   8.706
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   591.844
_cell_formula_units_Z   3
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  0.681  0.681  0.000  1.0
  K  K1  1  0.000  0.319  0.000  1.0
  K  K2  1  0.319  0.000  0.000  1.0
  K  K3  1  0.648  0.648  0.500  1.0
  K  K4  1  0.000  0.352  0.500  1.0
  K  K5  1  0.352  0.000  0.500  1.0
  Fe  Fe6  1  0.000  0.000  0.287  1.0
  Fe  Fe7  1  0.000  0.000  0.713  1.0
  Fe  Fe8  1  0.667  0.333  0.193  1.0
  Fe  Fe9  1  0.333  0.667  0.807  1.0
  Fe  Fe10  1  0.333  0.667  0.235  1.0
  Fe  Fe11  1  0.667  0.333  0.765  1.0
  B  B12  1  0.002  0.666  0.259  1.0
  B  B13  1  0.664  0.998  0.259  1.0
  B  B14  1  0.334  0.336  0.259  1.0
  B  B15  1  0.336  0.334  0.741  1.0
  B  B16  1  0.998  0.664  0.741  1.0
  B  B17  1  0.666  0.002  0.741  1.0
  O  O18  1  0.000  0.000  0.500  1.0
  O  O19  1  0.333  0.667  0.021  1.0
  O  O20  1  0.667  0.333  0.979  1.0
  O  O21  1  0.565  0.825  0.302  1.0
  O  O22  1  0.260  0.435  0.302  1.0
  O  O23  1  0.175  0.740  0.302  1.0
  O  O24  1  0.740  0.175  0.698  1.0
  O  O25  1  0.435  0.260  0.698  1.0
  O  O26  1  0.825  0.565  0.698  1.0
  O  O27  1  0.899  0.486  0.258  1.0
  O  O28  1  0.587  0.101  0.258  1.0
  O  O29  1  0.514  0.413  0.258  1.0
  O  O30  1  0.413  0.514  0.742  1.0
  O  O31  1  0.101  0.587  0.742  1.0
  O  O32  1  0.486  0.899  0.742  1.0
  O  O33  1  0.230  0.163  0.218  1.0
  O  O34  1  0.933  0.770  0.218  1.0
  O  O35  1  0.837  0.067  0.218  1.0
  O  O36  1  0.067  0.837  0.782  1.0
  O  O37  1  0.770  0.933  0.782  1.0
  O  O38  1  0.163  0.230  0.782  1.0
[/CIF]
.
The crystal structure described by K2Fe2B2O7 crystallizes in the trigonal P321 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1) and three equivalent O(5) atoms to form corner-sharing FeO4 tetrahedra. In the second Fe site, Fe(2) is bonded to one O(2) and three equivalent O(4) atoms to form corner-sharing FeO4 tetrahedra. In the third Fe site, Fe(3) is bonded to one O(2) and three equivalent O(3) atoms to form corner-sharing FeO4 tetrahedra. B(1) is bonded in a trigonal planar geometry to one O(3), one O(4), and one O(5) atom. There are five inequivalent O sites. In the first O site, O(5) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Fe(1), and one B(1) atom. In the second O site, O(1) is bonded in a distorted linear geometry to three equivalent K(2) and two equivalent Fe(1) atoms. In the third O site, O(2) is bonded in a distorted linear geometry to three equivalent K(1), one Fe(2), and one Fe(3) atom. In the fourth O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Fe(3), and one B(1) atom. In the fifth O site, O(4) is bonded in a 4-coordinate geometry to one K(1), one K(2), one Fe(2), and one B(1) atom. is represented by the CIF file [CIF]
data_K2Fe2B2O7
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   8.860
_cell_length_b   8.860
_cell_length_c   8.706
_cell_angle_alpha   90.000
_cell_angle_beta   90.000
_cell_angle_gamma   120.000
_symmetry_Int_Tables_number   1
_cell_volume   591.844
_cell_formula_units_Z   3
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  0.681  0.681  0.000  1.0
  K  K1  1  0.000  0.319  0.000  1.0
  K  K2  1  0.319  0.000  0.000  1.0
  K  K3  1  0.648  0.648  0.500  1.0
  K  K4  1  0.000  0.352  0.500  1.0
  K  K5  1  0.352  0.000  0.500  1.0
  Fe  Fe6  1  0.000  0.000  0.287  1.0
  Fe  Fe7  1  0.000  0.000  0.713  1.0
  Fe  Fe8  1  0.667  0.333  0.193  1.0
  Fe  Fe9  1  0.333  0.667  0.807  1.0
  Fe  Fe10  1  0.333  0.667  0.235  1.0
  Fe  Fe11  1  0.667  0.333  0.765  1.0
  B  B12  1  0.002  0.666  0.259  1.0
  B  B13  1  0.664  0.998  0.259  1.0
  B  B14  1  0.334  0.336  0.259  1.0
  B  B15  1  0.336  0.334  0.741  1.0
  B  B16  1  0.998  0.664  0.741  1.0
  B  B17  1  0.666  0.002  0.741  1.0
  O  O18  1  0.000  0.000  0.500  1.0
  O  O19  1  0.333  0.667  0.021  1.0
  O  O20  1  0.667  0.333  0.979  1.0
  O  O21  1  0.565  0.825  0.302  1.0
  O  O22  1  0.260  0.435  0.302  1.0
  O  O23  1  0.175  0.740  0.302  1.0
  O  O24  1  0.740  0.175  0.698  1.0
  O  O25  1  0.435  0.260  0.698  1.0
  O  O26  1  0.825  0.565  0.698  1.0
  O  O27  1  0.899  0.486  0.258  1.0
  O  O28  1  0.587  0.101  0.258  1.0
  O  O29  1  0.514  0.413  0.258  1.0
  O  O30  1  0.413  0.514  0.742  1.0
  O  O31  1  0.101  0.587  0.742  1.0
  O  O32  1  0.486  0.899  0.742  1.0
  O  O33  1  0.230  0.163  0.218  1.0
  O  O34  1  0.933  0.770  0.218  1.0
  O  O35  1  0.837  0.067  0.218  1.0
  O  O36  1  0.067  0.837  0.782  1.0
  O  O37  1  0.770  0.933  0.782  1.0
  O  O38  1  0.163  0.230  0.782  1.0
[/CIF]
.