The structure described by Mn4Nb2O9 is Ilmenite-like structured and crystallizes in the monoclinic Cc space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(5), one O(6), one O(8), and one O(9) atom to form distorted NbO6 octahedra that share corners with three equivalent Nb(2)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra,  a cornercorner with one Mn(3)O6 pentagonal pyramid, corners with two equivalent Mn(2)O6 pentagonal pyramids,  an edgeedge with one Mn(3)O6 pentagonal pyramid, and  a faceface with one Mn(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 39-42°. In the second Nb site, Nb(2) is bonded to one O(2), one O(3), one O(4), one O(6), one O(7), and one O(9) atom to form distorted NbO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra, corners with two equivalent Mn(3)O6 pentagonal pyramids, edges with two equivalent Mn(2)O6 pentagonal pyramids, and  a faceface with one Mn(3)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 39-47°. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(2)O6 octahedra,  a cornercorner with one Mn(2)O6 pentagonal pyramid,  an edgeedge with one Mn(2)O6 pentagonal pyramid, and edges with two equivalent Mn(3)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 39-47°. In the second Mn site, Mn(2) is bonded to one O(1), one O(2), one O(4), one O(6), one O(8), and one O(9) atom to form distorted MnO6 pentagonal pyramids that share  a cornercorner with one Mn(1)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, corners with three equivalent Mn(3)O6 pentagonal pyramids,  an edgeedge with one Mn(1)O6 octahedra, edges with two equivalent Nb(2)O6 octahedra, and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 57-67°. In the third Mn site, Mn(3) is bonded to one O(2), one O(3), one O(4), one O(5), one O(7), and one O(9) atom to form distorted MnO6 pentagonal pyramids that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, corners with three equivalent Mn(2)O6 pentagonal pyramids,  an edgeedge with one Nb(1)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra, and  a faceface with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-65°. In the fourth Mn site, Mn(4) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(8) atom. There are nine inequivalent O sites. In the first O site, O(9) is bonded in a distorted see-saw-like geometry to one Nb(1), one Nb(2), one Mn(2), and one Mn(3) atom. In the second O site, O(1) is bonded to one Nb(1), one Mn(1), one Mn(2), and one Mn(4) atom to form distorted corner-sharing OMn3Nb trigonal pyramids. In the third O site, O(2) is bonded in a distorted see-saw-like geometry to one Nb(1), one Nb(2), one Mn(2), and one Mn(3) atom. In the fourth O site, O(3) is bonded in a distorted see-saw-like geometry to one Nb(2), one Mn(1), one Mn(3), and one Mn(4) atom. In the fifth O site, O(4) is bonded to one Nb(2), one Mn(1), one Mn(2), and one Mn(3) atom to form distorted corner-sharing OMn3Nb trigonal pyramids. In the sixth O site, O(5) is bonded in a distorted see-saw-like geometry to one Nb(1), one Mn(1), one Mn(3), and one Mn(4) atom. In the seventh O site, O(6) is bonded in a distorted see-saw-like geometry to one Nb(1), one Nb(2), one Mn(2), and one Mn(4) atom. In the eighth O site, O(7) is bonded in a distorted see-saw-like geometry to one Nb(2), one Mn(1), one Mn(3), and one Mn(4) atom. In the ninth O site, O(8) is bonded in a distorted see-saw-like geometry to one Nb(1), one Mn(1), one Mn(2), and one Mn(4) atom. is represented by the CIF file [CIF]
data_Mn4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.731
_cell_length_b   5.731
_cell_length_c   13.421
_cell_angle_alpha   87.593
_cell_angle_beta   87.593
_cell_angle_gamma   56.216
_symmetry_Int_Tables_number   1
_cell_volume   365.892
_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
  Mn  Mn0  1  0.995  0.996  0.499  1.0
  Mn  Mn1  1  0.996  0.995  0.999  1.0
  Mn  Mn2  1  0.952  0.962  0.738  1.0
  Mn  Mn3  1  0.626  0.612  0.405  1.0
  Mn  Mn4  1  0.293  0.292  0.074  1.0
  Mn  Mn5  1  0.962  0.952  0.238  1.0
  Mn  Mn6  1  0.612  0.626  0.905  1.0
  Mn  Mn7  1  0.292  0.293  0.574  1.0
  Nb  Nb8  1  0.674  0.662  0.162  1.0
  Nb  Nb9  1  0.323  0.342  0.840  1.0
  Nb  Nb10  1  0.662  0.674  0.662  1.0
  Nb  Nb11  1  0.342  0.323  0.340  1.0
  O  O12  1  0.720  0.971  0.604  1.0
  O  O13  1  0.403  0.653  0.258  1.0
  O  O14  1  0.056  0.323  0.923  1.0
  O  O15  1  0.747  0.175  0.369  1.0
  O  O16  1  0.442  0.822  0.047  1.0
  O  O17  1  0.101  0.484  0.714  1.0
  O  O18  1  0.259  0.572  0.456  1.0
  O  O19  1  0.899  0.273  0.133  1.0
  O  O20  1  0.574  0.939  0.797  1.0
  O  O21  1  0.273  0.899  0.633  1.0
  O  O22  1  0.939  0.574  0.297  1.0
  O  O23  1  0.572  0.259  0.956  1.0
  O  O24  1  0.822  0.442  0.547  1.0
  O  O25  1  0.484  0.101  0.214  1.0
  O  O26  1  0.175  0.747  0.869  1.0
  O  O27  1  0.323  0.056  0.423  1.0
  O  O28  1  0.971  0.720  0.104  1.0
  O  O29  1  0.653  0.403  0.758  1.0
[/CIF]
.
The structure described by Mn4Nb2O9 is Ilmenite-like structured and crystallizes in the monoclinic Cc space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(5), one O(6), one O(8), and one O(9) atom to form distorted NbO6 octahedra that share corners with three equivalent Nb(2)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra,  a cornercorner with one Mn(3)O6 pentagonal pyramid, corners with two equivalent Mn(2)O6 pentagonal pyramids,  an edgeedge with one Mn(3)O6 pentagonal pyramid, and  a faceface with one Mn(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 39-42°. In the second Nb site, Nb(2) is bonded to one O(2), one O(3), one O(4), one O(6), one O(7), and one O(9) atom to form distorted NbO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra, corners with two equivalent Mn(3)O6 pentagonal pyramids, edges with two equivalent Mn(2)O6 pentagonal pyramids, and  a faceface with one Mn(3)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 39-47°. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(2)O6 octahedra,  a cornercorner with one Mn(2)O6 pentagonal pyramid,  an edgeedge with one Mn(2)O6 pentagonal pyramid, and edges with two equivalent Mn(3)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 39-47°. In the second Mn site, Mn(2) is bonded to one O(1), one O(2), one O(4), one O(6), one O(8), and one O(9) atom to form distorted MnO6 pentagonal pyramids that share  a cornercorner with one Mn(1)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, corners with three equivalent Mn(3)O6 pentagonal pyramids,  an edgeedge with one Mn(1)O6 octahedra, edges with two equivalent Nb(2)O6 octahedra, and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 57-67°. In the third Mn site, Mn(3) is bonded to one O(2), one O(3), one O(4), one O(5), one O(7), and one O(9) atom to form distorted MnO6 pentagonal pyramids that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(2)O6 octahedra, corners with three equivalent Mn(2)O6 pentagonal pyramids,  an edgeedge with one Nb(1)O6 octahedra, edges with two equivalent Mn(1)O6 octahedra, and  a faceface with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 59-65°. In the fourth Mn site, Mn(4) is bonded in a 6-coordinate geometry to one O(1), one O(3), one O(5), one O(6), one O(7), and one O(8) atom. There are nine inequivalent O sites. In the first O site, O(9) is bonded in a distorted see-saw-like geometry to one Nb(1), one Nb(2), one Mn(2), and one Mn(3) atom. In the second O site, O(1) is bonded to one Nb(1), one Mn(1), one Mn(2), and one Mn(4) atom to form distorted corner-sharing OMn3Nb trigonal pyramids. In the third O site, O(2) is bonded in a distorted see-saw-like geometry to one Nb(1), one Nb(2), one Mn(2), and one Mn(3) atom. In the fourth O site, O(3) is bonded in a distorted see-saw-like geometry to one Nb(2), one Mn(1), one Mn(3), and one Mn(4) atom. In the fifth O site, O(4) is bonded to one Nb(2), one Mn(1), one Mn(2), and one Mn(3) atom to form distorted corner-sharing OMn3Nb trigonal pyramids. In the sixth O site, O(5) is bonded in a distorted see-saw-like geometry to one Nb(1), one Mn(1), one Mn(3), and one Mn(4) atom. In the seventh O site, O(6) is bonded in a distorted see-saw-like geometry to one Nb(1), one Nb(2), one Mn(2), and one Mn(4) atom. In the eighth O site, O(7) is bonded in a distorted see-saw-like geometry to one Nb(2), one Mn(1), one Mn(3), and one Mn(4) atom. In the ninth O site, O(8) is bonded in a distorted see-saw-like geometry to one Nb(1), one Mn(1), one Mn(2), and one Mn(4) atom. is represented by the CIF file [CIF]
data_Mn4Nb2O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.731
_cell_length_b   5.731
_cell_length_c   13.421
_cell_angle_alpha   87.593
_cell_angle_beta   87.593
_cell_angle_gamma   56.216
_symmetry_Int_Tables_number   1
_cell_volume   365.892
_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
  Mn  Mn0  1  0.995  0.996  0.499  1.0
  Mn  Mn1  1  0.996  0.995  0.999  1.0
  Mn  Mn2  1  0.952  0.962  0.738  1.0
  Mn  Mn3  1  0.626  0.612  0.405  1.0
  Mn  Mn4  1  0.293  0.292  0.074  1.0
  Mn  Mn5  1  0.962  0.952  0.238  1.0
  Mn  Mn6  1  0.612  0.626  0.905  1.0
  Mn  Mn7  1  0.292  0.293  0.574  1.0
  Nb  Nb8  1  0.674  0.662  0.162  1.0
  Nb  Nb9  1  0.323  0.342  0.840  1.0
  Nb  Nb10  1  0.662  0.674  0.662  1.0
  Nb  Nb11  1  0.342  0.323  0.340  1.0
  O  O12  1  0.720  0.971  0.604  1.0
  O  O13  1  0.403  0.653  0.258  1.0
  O  O14  1  0.056  0.323  0.923  1.0
  O  O15  1  0.747  0.175  0.369  1.0
  O  O16  1  0.442  0.822  0.047  1.0
  O  O17  1  0.101  0.484  0.714  1.0
  O  O18  1  0.259  0.572  0.456  1.0
  O  O19  1  0.899  0.273  0.133  1.0
  O  O20  1  0.574  0.939  0.797  1.0
  O  O21  1  0.273  0.899  0.633  1.0
  O  O22  1  0.939  0.574  0.297  1.0
  O  O23  1  0.572  0.259  0.956  1.0
  O  O24  1  0.822  0.442  0.547  1.0
  O  O25  1  0.484  0.101  0.214  1.0
  O  O26  1  0.175  0.747  0.869  1.0
  O  O27  1  0.323  0.056  0.423  1.0
  O  O28  1  0.971  0.720  0.104  1.0
  O  O29  1  0.653  0.403  0.758  1.0
[/CIF]
.