The material described by Nb9As2O25 crystallizes in the tetragonal I4/m space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(5) and four O(6,6) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. In the second Nb site, Nb(2) is bonded to one O(1), one O(3), one O(6), one O(7), and two equivalent O(2) atoms to form a mixture of edge and corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 3-24°. In the third Nb site, Nb(3) is bonded to one O(2), one O(3), one O(4), one O(7), and two equivalent O(1) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 8-28°. As(1) is bonded to four equivalent O(4) atoms to form distorted AsO4 tetrahedra that share corners with four equivalent Nb(3)O6 octahedra and edges with two equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 51°. There are nine inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one Nb(3) and two equivalent As(1) atoms. In the second O site, O(6) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the third O site, O(5) is bonded in a linear geometry to two equivalent Nb(1) atoms. In the fourth O site, O(6) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the fifth O site, O(6) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the sixth O site, O(7) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. In the seventh O site, O(1) is bonded in a distorted T-shaped geometry to one Nb(2) and two equivalent Nb(3) atoms. In the eighth O site, O(2) is bonded in a distorted T-shaped geometry to one Nb(3) and two equivalent Nb(2) atoms. In the ninth O site, O(3) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. is represented by the CIF card [CIF]
data_Nb9As2O25
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   11.571
_cell_length_b   11.571
_cell_length_c   11.571
_cell_angle_alpha   91.751
_cell_angle_beta   91.751
_cell_angle_gamma   159.868
_symmetry_Int_Tables_number   1
_cell_volume   525.032
_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
  Nb  Nb0  1  0.000  0.000  0.000  1.0
  Nb  Nb1  1  0.221  0.899  0.121  1.0
  Nb  Nb2  1  0.779  0.101  0.879  1.0
  Nb  Nb3  1  0.899  0.779  0.678  1.0
  Nb  Nb4  1  0.101  0.221  0.322  1.0
  Nb  Nb5  1  0.125  0.681  0.806  1.0
  Nb  Nb6  1  0.875  0.319  0.194  1.0
  Nb  Nb7  1  0.681  0.875  0.557  1.0
  Nb  Nb8  1  0.319  0.125  0.443  1.0
  As  As9  1  0.750  0.250  0.500  1.0
  As  As10  1  0.250  0.750  0.500  1.0
  O  O11  1  0.350  0.837  0.187  1.0
  O  O12  1  0.650  0.163  0.813  1.0
  O  O13  1  0.837  0.650  0.487  1.0
  O  O14  1  0.163  0.350  0.513  1.0
  O  O15  1  0.254  0.612  0.866  1.0
  O  O16  1  0.746  0.388  0.134  1.0
  O  O17  1  0.612  0.746  0.358  1.0
  O  O18  1  0.388  0.254  0.642  1.0
  O  O19  1  0.181  0.787  0.968  1.0
  O  O20  1  0.819  0.213  0.032  1.0
  O  O21  1  0.787  0.819  0.606  1.0
  O  O22  1  0.213  0.181  0.394  1.0
  O  O23  1  0.094  0.559  0.653  1.0
  O  O24  1  0.906  0.441  0.347  1.0
  O  O25  1  0.559  0.906  0.464  1.0
  O  O26  1  0.441  0.094  0.536  1.0
  O  O27  1  0.500  0.500  0.000  1.0
  O  O28  1  0.117  0.950  0.067  1.0
  O  O29  1  0.883  0.050  0.933  1.0
  O  O30  1  0.950  0.883  0.833  1.0
  O  O31  1  0.050  0.117  0.167  1.0
  O  O32  1  0.016  0.719  0.735  1.0
  O  O33  1  0.984  0.281  0.265  1.0
  O  O34  1  0.719  0.984  0.702  1.0
  O  O35  1  0.281  0.016  0.298  1.0
[/CIF]
.
The material described by Nb9As2O25 crystallizes in the tetragonal I4/m space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(5) and four O(6,6) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. In the second Nb site, Nb(2) is bonded to one O(1), one O(3), one O(6), one O(7), and two equivalent O(2) atoms to form a mixture of edge and corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 3-24°. In the third Nb site, Nb(3) is bonded to one O(2), one O(3), one O(4), one O(7), and two equivalent O(1) atoms to form distorted NbO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 8-28°. As(1) is bonded to four equivalent O(4) atoms to form distorted AsO4 tetrahedra that share corners with four equivalent Nb(3)O6 octahedra and edges with two equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 51°. There are nine inequivalent O sites. In the first O site, O(4) is bonded in a 3-coordinate geometry to one Nb(3) and two equivalent As(1) atoms. In the second O site, O(6) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the third O site, O(5) is bonded in a linear geometry to two equivalent Nb(1) atoms. In the fourth O site, O(6) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the fifth O site, O(6) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the sixth O site, O(7) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. In the seventh O site, O(1) is bonded in a distorted T-shaped geometry to one Nb(2) and two equivalent Nb(3) atoms. In the eighth O site, O(2) is bonded in a distorted T-shaped geometry to one Nb(3) and two equivalent Nb(2) atoms. In the ninth O site, O(3) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. is represented by the CIF card [CIF]
data_Nb9As2O25
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   11.571
_cell_length_b   11.571
_cell_length_c   11.571
_cell_angle_alpha   91.751
_cell_angle_beta   91.751
_cell_angle_gamma   159.868
_symmetry_Int_Tables_number   1
_cell_volume   525.032
_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
  Nb  Nb0  1  0.000  0.000  0.000  1.0
  Nb  Nb1  1  0.221  0.899  0.121  1.0
  Nb  Nb2  1  0.779  0.101  0.879  1.0
  Nb  Nb3  1  0.899  0.779  0.678  1.0
  Nb  Nb4  1  0.101  0.221  0.322  1.0
  Nb  Nb5  1  0.125  0.681  0.806  1.0
  Nb  Nb6  1  0.875  0.319  0.194  1.0
  Nb  Nb7  1  0.681  0.875  0.557  1.0
  Nb  Nb8  1  0.319  0.125  0.443  1.0
  As  As9  1  0.750  0.250  0.500  1.0
  As  As10  1  0.250  0.750  0.500  1.0
  O  O11  1  0.350  0.837  0.187  1.0
  O  O12  1  0.650  0.163  0.813  1.0
  O  O13  1  0.837  0.650  0.487  1.0
  O  O14  1  0.163  0.350  0.513  1.0
  O  O15  1  0.254  0.612  0.866  1.0
  O  O16  1  0.746  0.388  0.134  1.0
  O  O17  1  0.612  0.746  0.358  1.0
  O  O18  1  0.388  0.254  0.642  1.0
  O  O19  1  0.181  0.787  0.968  1.0
  O  O20  1  0.819  0.213  0.032  1.0
  O  O21  1  0.787  0.819  0.606  1.0
  O  O22  1  0.213  0.181  0.394  1.0
  O  O23  1  0.094  0.559  0.653  1.0
  O  O24  1  0.906  0.441  0.347  1.0
  O  O25  1  0.559  0.906  0.464  1.0
  O  O26  1  0.441  0.094  0.536  1.0
  O  O27  1  0.500  0.500  0.000  1.0
  O  O28  1  0.117  0.950  0.067  1.0
  O  O29  1  0.883  0.050  0.933  1.0
  O  O30  1  0.950  0.883  0.833  1.0
  O  O31  1  0.050  0.117  0.167  1.0
  O  O32  1  0.016  0.719  0.735  1.0
  O  O33  1  0.984  0.281  0.265  1.0
  O  O34  1  0.719  0.984  0.702  1.0
  O  O35  1  0.281  0.016  0.298  1.0
[/CIF]
.