The structure described by NdNb3O9 crystallizes in the monoclinic C2/m space group. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to two equivalent O(13), two equivalent O(8), four equivalent O(11), and four equivalent O(2) atoms to form NdO12 cuboctahedra that share corners with four equivalent Nd(2)O12 cuboctahedra, faces with two equivalent Nd(3)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Nb(3)O6 octahedra. In the second Nd site, Nd(2) is bonded to one O(10), one O(12), one O(5), one O(9), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(7) atoms to form NdO12 cuboctahedra that share corners with two equivalent Nd(1)O12 cuboctahedra, corners with two equivalent Nd(2)O12 cuboctahedra,  a faceface with one Nd(3)O12 cuboctahedra, faces with two equivalent Nb(1)O6 octahedra, faces with two equivalent Nb(3)O6 octahedra, and faces with four equivalent Nb(2)O6 octahedra. In the third Nd site, Nd(3) is bonded to two equivalent O(12), two equivalent O(9), four equivalent O(11), and four equivalent O(2) atoms to form NdO12 cuboctahedra that share faces with two equivalent Nd(1)O12 cuboctahedra, faces with two equivalent Nd(2)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Nb(3)O6 octahedra. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(11), one O(12), one O(13), one O(2), and one O(3) atom to form NbO6 octahedra that share  a cornercorner with one Nb(2)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra,  a faceface with one Nd(1)O12 cuboctahedra,  a faceface with one Nd(2)O12 cuboctahedra, and  a faceface with one Nd(3)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-20°. In the second Nb site, Nb(2) is bonded to one O(10), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form NbO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra, corners with three equivalent Nb(2)O6 octahedra, and faces with two equivalent Nd(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-14°. In the third Nb site, Nb(3) is bonded to one O(11), one O(2), one O(6), one O(7), one O(8), and one O(9) atom to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra,  a faceface with one Nd(1)O12 cuboctahedra,  a faceface with one Nd(2)O12 cuboctahedra, and  a faceface with one Nd(3)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-20°. There are thirteen inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to one Nd(1), one Nd(2), one Nd(3), one Nb(1), and one Nb(3) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Nd(2), one Nb(1), and one Nb(2) atom. In the fourth O site, O(4) is bonded in a distorted linear geometry to two equivalent Nd(2) and two equivalent Nb(2) atoms. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Nd(2) and two equivalent Nb(2) atoms. In the sixth O site, O(6) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Nd(2), one Nb(2), and one Nb(3) atom. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to one Nd(1) and two equivalent Nb(3) atoms. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(3), and two equivalent Nb(3) atoms. In the tenth O site, O(10) is bonded in a distorted T-shaped geometry to one Nd(2) and two equivalent Nb(2) atoms. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one Nd(1), one Nd(3), one Nb(1), and one Nb(3) atom. In the twelfth O site, O(12) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(3), and two equivalent Nb(1) atoms. In the thirteenth O site, O(13) is bonded in a distorted T-shaped geometry to one Nd(1) and two equivalent Nb(1) atoms. is represented by the CIF card [CIF]
data_NdNb3O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   16.820
_cell_length_b   12.547
_cell_length_c   9.777
_cell_angle_alpha   59.122
_cell_angle_beta   54.998
_cell_angle_gamma   26.543
_symmetry_Int_Tables_number   1
_cell_volume   755.228
_cell_formula_units_Z   4
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
  Nd  Nd0  1  0.000  0.000  0.000  1.0
  Nd  Nd1  1  0.333  0.002  0.999  1.0
  Nd  Nd2  1  0.667  0.998  0.001  1.0
  Nd  Nd3  1  0.500  0.500  0.000  1.0
  Nb  Nb4  1  0.075  0.009  0.257  1.0
  Nb  Nb5  1  0.415  0.001  0.253  1.0
  Nb  Nb6  1  0.249  0.007  0.738  1.0
  Nb  Nb7  1  0.244  0.500  0.262  1.0
  Nb  Nb8  1  0.084  0.499  0.747  1.0
  Nb  Nb9  1  0.751  0.993  0.262  1.0
  Nb  Nb10  1  0.585  0.999  0.747  1.0
  Nb  Nb11  1  0.583  0.502  0.257  1.0
  Nb  Nb12  1  0.417  0.498  0.743  1.0
  Nb  Nb13  1  0.925  0.991  0.743  1.0
  Nb  Nb14  1  0.916  0.501  0.253  1.0
  Nb  Nb15  1  0.756  0.500  0.738  1.0
  O  O16  1  0.000  0.000  0.500  1.0
  O  O17  1  0.175  0.986  0.001  1.0
  O  O18  1  0.012  0.244  0.231  1.0
  O  O19  1  0.000  0.500  0.000  1.0
  O  O20  1  0.179  0.232  0.230  1.0
  O  O21  1  0.500  0.000  0.000  1.0
  O  O22  1  0.334  0.999  0.499  1.0
  O  O23  1  0.344  0.248  0.231  1.0
  O  O24  1  0.166  0.243  0.769  1.0
  O  O25  1  0.998  0.776  0.229  1.0
  O  O26  1  0.166  0.501  0.501  1.0
  O  O27  1  0.337  0.501  0.999  1.0
  O  O28  1  0.512  0.246  0.218  1.0
  O  O29  1  0.333  0.232  0.770  1.0
  O  O30  1  0.190  0.735  0.221  1.0
  O  O31  1  0.825  0.014  0.999  1.0
  O  O32  1  0.666  0.001  0.501  1.0
  O  O33  1  0.663  0.263  0.221  1.0
  O  O34  1  0.498  0.247  0.769  1.0
  O  O35  1  0.342  0.753  0.220  1.0
  O  O36  1  0.151  0.778  0.769  1.0
  O  O37  1  0.500  0.500  0.500  1.0
  O  O38  1  0.663  0.499  0.001  1.0
  O  O39  1  0.849  0.222  0.231  1.0
  O  O40  1  0.658  0.247  0.780  1.0
  O  O41  1  0.502  0.753  0.231  1.0
  O  O42  1  0.337  0.737  0.779  1.0
  O  O43  1  0.810  0.265  0.779  1.0
  O  O44  1  0.667  0.768  0.230  1.0
  O  O45  1  0.488  0.754  0.782  1.0
  O  O46  1  0.834  0.499  0.499  1.0
  O  O47  1  0.002  0.224  0.771  1.0
  O  O48  1  0.656  0.752  0.769  1.0
  O  O49  1  0.834  0.757  0.231  1.0
  O  O50  1  0.821  0.768  0.770  1.0
  O  O51  1  0.988  0.756  0.769  1.0
[/CIF]
.
The structure described by NdNb3O9 crystallizes in the monoclinic C2/m space group. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to two equivalent O(13), two equivalent O(8), four equivalent O(11), and four equivalent O(2) atoms to form NdO12 cuboctahedra that share corners with four equivalent Nd(2)O12 cuboctahedra, faces with two equivalent Nd(3)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Nb(3)O6 octahedra. In the second Nd site, Nd(2) is bonded to one O(10), one O(12), one O(5), one O(9), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(7) atoms to form NdO12 cuboctahedra that share corners with two equivalent Nd(1)O12 cuboctahedra, corners with two equivalent Nd(2)O12 cuboctahedra,  a faceface with one Nd(3)O12 cuboctahedra, faces with two equivalent Nb(1)O6 octahedra, faces with two equivalent Nb(3)O6 octahedra, and faces with four equivalent Nb(2)O6 octahedra. In the third Nd site, Nd(3) is bonded to two equivalent O(12), two equivalent O(9), four equivalent O(11), and four equivalent O(2) atoms to form NdO12 cuboctahedra that share faces with two equivalent Nd(1)O12 cuboctahedra, faces with two equivalent Nd(2)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Nb(3)O6 octahedra. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(11), one O(12), one O(13), one O(2), and one O(3) atom to form NbO6 octahedra that share  a cornercorner with one Nb(2)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra,  a faceface with one Nd(1)O12 cuboctahedra,  a faceface with one Nd(2)O12 cuboctahedra, and  a faceface with one Nd(3)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-20°. In the second Nb site, Nb(2) is bonded to one O(10), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form NbO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra, corners with three equivalent Nb(2)O6 octahedra, and faces with two equivalent Nd(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-14°. In the third Nb site, Nb(3) is bonded to one O(11), one O(2), one O(6), one O(7), one O(8), and one O(9) atom to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, corners with two equivalent Nb(3)O6 octahedra,  a faceface with one Nd(1)O12 cuboctahedra,  a faceface with one Nd(2)O12 cuboctahedra, and  a faceface with one Nd(3)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-20°. There are thirteen inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Nb(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to one Nd(1), one Nd(2), one Nd(3), one Nb(1), and one Nb(3) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Nd(2), one Nb(1), and one Nb(2) atom. In the fourth O site, O(4) is bonded in a distorted linear geometry to two equivalent Nd(2) and two equivalent Nb(2) atoms. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Nd(2) and two equivalent Nb(2) atoms. In the sixth O site, O(6) is bonded in a linear geometry to one Nb(2) and one Nb(3) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Nd(2), one Nb(2), and one Nb(3) atom. In the eighth O site, O(8) is bonded in a distorted T-shaped geometry to one Nd(1) and two equivalent Nb(3) atoms. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(3), and two equivalent Nb(3) atoms. In the tenth O site, O(10) is bonded in a distorted T-shaped geometry to one Nd(2) and two equivalent Nb(2) atoms. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one Nd(1), one Nd(3), one Nb(1), and one Nb(3) atom. In the twelfth O site, O(12) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(3), and two equivalent Nb(1) atoms. In the thirteenth O site, O(13) is bonded in a distorted T-shaped geometry to one Nd(1) and two equivalent Nb(1) atoms. is represented by the CIF card [CIF]
data_NdNb3O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   16.820
_cell_length_b   12.547
_cell_length_c   9.777
_cell_angle_alpha   59.122
_cell_angle_beta   54.998
_cell_angle_gamma   26.543
_symmetry_Int_Tables_number   1
_cell_volume   755.228
_cell_formula_units_Z   4
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
  Nd  Nd0  1  0.000  0.000  0.000  1.0
  Nd  Nd1  1  0.333  0.002  0.999  1.0
  Nd  Nd2  1  0.667  0.998  0.001  1.0
  Nd  Nd3  1  0.500  0.500  0.000  1.0
  Nb  Nb4  1  0.075  0.009  0.257  1.0
  Nb  Nb5  1  0.415  0.001  0.253  1.0
  Nb  Nb6  1  0.249  0.007  0.738  1.0
  Nb  Nb7  1  0.244  0.500  0.262  1.0
  Nb  Nb8  1  0.084  0.499  0.747  1.0
  Nb  Nb9  1  0.751  0.993  0.262  1.0
  Nb  Nb10  1  0.585  0.999  0.747  1.0
  Nb  Nb11  1  0.583  0.502  0.257  1.0
  Nb  Nb12  1  0.417  0.498  0.743  1.0
  Nb  Nb13  1  0.925  0.991  0.743  1.0
  Nb  Nb14  1  0.916  0.501  0.253  1.0
  Nb  Nb15  1  0.756  0.500  0.738  1.0
  O  O16  1  0.000  0.000  0.500  1.0
  O  O17  1  0.175  0.986  0.001  1.0
  O  O18  1  0.012  0.244  0.231  1.0
  O  O19  1  0.000  0.500  0.000  1.0
  O  O20  1  0.179  0.232  0.230  1.0
  O  O21  1  0.500  0.000  0.000  1.0
  O  O22  1  0.334  0.999  0.499  1.0
  O  O23  1  0.344  0.248  0.231  1.0
  O  O24  1  0.166  0.243  0.769  1.0
  O  O25  1  0.998  0.776  0.229  1.0
  O  O26  1  0.166  0.501  0.501  1.0
  O  O27  1  0.337  0.501  0.999  1.0
  O  O28  1  0.512  0.246  0.218  1.0
  O  O29  1  0.333  0.232  0.770  1.0
  O  O30  1  0.190  0.735  0.221  1.0
  O  O31  1  0.825  0.014  0.999  1.0
  O  O32  1  0.666  0.001  0.501  1.0
  O  O33  1  0.663  0.263  0.221  1.0
  O  O34  1  0.498  0.247  0.769  1.0
  O  O35  1  0.342  0.753  0.220  1.0
  O  O36  1  0.151  0.778  0.769  1.0
  O  O37  1  0.500  0.500  0.500  1.0
  O  O38  1  0.663  0.499  0.001  1.0
  O  O39  1  0.849  0.222  0.231  1.0
  O  O40  1  0.658  0.247  0.780  1.0
  O  O41  1  0.502  0.753  0.231  1.0
  O  O42  1  0.337  0.737  0.779  1.0
  O  O43  1  0.810  0.265  0.779  1.0
  O  O44  1  0.667  0.768  0.230  1.0
  O  O45  1  0.488  0.754  0.782  1.0
  O  O46  1  0.834  0.499  0.499  1.0
  O  O47  1  0.002  0.224  0.771  1.0
  O  O48  1  0.656  0.752  0.769  1.0
  O  O49  1  0.834  0.757  0.231  1.0
  O  O50  1  0.821  0.768  0.770  1.0
  O  O51  1  0.988  0.756  0.769  1.0
[/CIF]
.