The structure described by Co4Nb2O9 is Ilmenite-like structured and crystallizes in the triclinic P1 space group. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form distorted NbO6 octahedra that share corners with three equivalent Co(5)O6 octahedra, corners with three equivalent Co(6)O6 octahedra, corners with three equivalent Co(7)O6 octahedra, edges with three equivalent Co(3)O6 octahedra, and  a faceface with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-57°. In the second Nb site, Nb(2) is bonded to one O(10), one O(11), one O(12), one O(4), one O(5), and one O(6) atom to form distorted NbO6 octahedra that share corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Co(2)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, edges with three equivalent Co(7)O6 octahedra, and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the third Nb site, Nb(3) is bonded to one O(1), one O(13), one O(14), one O(15), one O(2), and one O(3) atom to form distorted NbO6 octahedra that share corners with three equivalent Co(5)O6 octahedra, corners with three equivalent Co(6)O6 octahedra, corners with three equivalent Co(8)O6 octahedra, edges with three equivalent Co(4)O6 octahedra, and  a faceface with one Nb(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-57°. In the fourth Nb site, Nb(4) is bonded to one O(1), one O(16), one O(17), one O(18), one O(2), and one O(3) atom to form distorted NbO6 octahedra that share corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Co(2)O6 octahedra, corners with three equivalent Co(4)O6 octahedra, edges with three equivalent Co(8)O6 octahedra, and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. There are eight inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(10), one O(11), one O(12), one O(16), one O(17), and one O(18) atom to form CoO6 octahedra that share corners with three equivalent Nb(2)O6 octahedra, corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Co(8)O6 octahedra, edges with three equivalent Co(2)O6 octahedra, and  a faceface with one Co(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the second Co site, Co(2) is bonded to one O(10), one O(11), one O(12), one O(16), one O(17), and one O(18) atom to form CoO6 octahedra that share corners with three equivalent Nb(2)O6 octahedra, corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Co(7)O6 octahedra, edges with three equivalent Co(1)O6 octahedra, and  a faceface with one Co(8)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the third Co site, Co(3) is bonded to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form distorted CoO6 octahedra that share corners with three equivalent Nb(2)O6 octahedra, corners with three equivalent Co(6)O6 octahedra, corners with three equivalent Co(7)O6 octahedra, edges with three equivalent Nb(1)O6 octahedra, and  a faceface with one Co(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-66°. In the fourth Co site, Co(4) is bonded to one O(1), one O(13), one O(14), one O(15), one O(2), and one O(3) atom to form distorted CoO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Co(5)O6 octahedra, corners with three equivalent Co(8)O6 octahedra, edges with three equivalent Nb(3)O6 octahedra, and  a faceface with one Co(6)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-66°. In the fifth Co site, Co(5) is bonded to one O(13), one O(14), one O(15), one O(7), one O(8), and one O(9) atom to form CoO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, corners with three equivalent Co(4)O6 octahedra, edges with three equivalent Co(6)O6 octahedra, and  a faceface with one Co(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the sixth Co site, Co(6) is bonded to one O(13), one O(14), one O(15), one O(7), one O(8), and one O(9) atom to form CoO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, edges with three equivalent Co(5)O6 octahedra, and  a faceface with one Co(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-57°. In the seventh Co site, Co(7) is bonded to one O(10), one O(11), one O(12), one O(4), one O(5), and one O(6) atom to form distorted CoO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Co(2)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, edges with three equivalent Nb(2)O6 octahedra, and  a faceface with one Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-66°. In the eighth Co site, Co(8) is bonded to one O(1), one O(16), one O(17), one O(18), one O(2), and one O(3) atom to form distorted CoO6 octahedra that share corners with three equivalent Nb(3)O6 octahedra, corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Co(4)O6 octahedra, edges with three equivalent Nb(4)O6 octahedra, and  a faceface with one Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-66°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded to one Nb(3), one Nb(4), one Co(4), and one Co(8) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(2)Nb2Co2 trigonal pyramid,  an edgeedge with one O(3)Nb2Co2 trigonal pyramid,  an edgeedge with one O(13)NbCo3 trigonal pyramid, and  an edgeedge with one O(17)NbCo3 trigonal pyramid. In the second O site, O(2) is bonded to one Nb(3), one Nb(4), one Co(4), and one Co(8) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(1)Nb2Co2 trigonal pyramid,  an edgeedge with one O(3)Nb2Co2 trigonal pyramid,  an edgeedge with one O(14)NbCo3 trigonal pyramid, and  an edgeedge with one O(16)NbCo3 trigonal pyramid. In the third O site, O(3) is bonded to one Nb(3), one Nb(4), one Co(4), and one Co(8) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids,  an edgeedge with one O(1)Nb2Co2 trigonal pyramid,  an edgeedge with one O(2)Nb2Co2 trigonal pyramid,  an edgeedge with one O(15)NbCo3 trigonal pyramid, and  an edgeedge with one O(18)NbCo3 trigonal pyramid. In the fourth O site, O(4) is bonded to one Nb(1), one Nb(2), one Co(3), and one Co(7) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(5)Nb2Co2 trigonal pyramid,  an edgeedge with one O(6)Nb2Co2 trigonal pyramid,  an edgeedge with one O(11)NbCo3 trigonal pyramid, and  an edgeedge with one O(7)NbCo3 trigonal pyramid. In the fifth O site, O(5) is bonded to one Nb(1), one Nb(2), one Co(3), and one Co(7) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(4)Nb2Co2 trigonal pyramid,  an edgeedge with one O(6)Nb2Co2 trigonal pyramid,  an edgeedge with one O(10)NbCo3 trigonal pyramid, and  an edgeedge with one O(8)NbCo3 trigonal pyramid. In the sixth O site, O(6) is bonded to one Nb(1), one Nb(2), one Co(3), and one Co(7) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids,  an edgeedge with one O(4)Nb2Co2 trigonal pyramid,  an edgeedge with one O(5)Nb2Co2 trigonal pyramid,  an edgeedge with one O(12)NbCo3 trigonal pyramid, and  an edgeedge with one O(9)NbCo3 trigonal pyramid. In the seventh O site, O(7) is bonded to one Nb(1), one Co(3), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(4)Nb2Co2 trigonal pyramid,  an edgeedge with one O(13)NbCo3 trigonal pyramid,  an edgeedge with one O(8)NbCo3 trigonal pyramid, and  an edgeedge with one O(9)NbCo3 trigonal pyramid. In the eighth O site, O(8) is bonded to one Nb(1), one Co(3), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(5)Nb2Co2 trigonal pyramid,  an edgeedge with one O(14)NbCo3 trigonal pyramid,  an edgeedge with one O(7)NbCo3 trigonal pyramid, and  an edgeedge with one O(9)NbCo3 trigonal pyramid. In the ninth O site, O(9) is bonded to one Nb(1), one Co(3), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids,  an edgeedge with one O(6)Nb2Co2 trigonal pyramid,  an edgeedge with one O(15)NbCo3 trigonal pyramid,  an edgeedge with one O(7)NbCo3 trigonal pyramid, and  an edgeedge with one O(8)NbCo3 trigonal pyramid. In the tenth O site, O(10) is bonded to one Nb(2), one Co(1), one Co(2), and one Co(7) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(5)Nb2Co2 trigonal pyramid,  an edgeedge with one O(11)NbCo3 trigonal pyramid,  an edgeedge with one O(12)NbCo3 trigonal pyramid, and  an edgeedge with one O(16)NbCo3 trigonal pyramid. In the eleventh O site, O(11) is bonded to one Nb(2), one Co(1), one Co(2), and one Co(7) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(4)Nb2Co2 trigonal pyramid,  an edgeedge with one O(10)NbCo3 trigonal pyramid,  an edgeedge with one O(12)NbCo3 trigonal pyramid, and  an edgeedge with one O(17)NbCo3 trigonal pyramid. In the twelfth O site, O(12) is bonded to one Nb(2), one Co(1), one Co(2), and one Co(7) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids,  an edgeedge with one O(6)Nb2Co2 trigonal pyramid,  an edgeedge with one O(10)NbCo3 trigonal pyramid,  an edgeedge with one O(11)NbCo3 trigonal pyramid, and  an edgeedge with one O(18)NbCo3 trigonal pyramid. In the thirteenth O site, O(13) is bonded to one Nb(3), one Co(4), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(1)Nb2Co2 trigonal pyramid,  an edgeedge with one O(14)NbCo3 trigonal pyramid,  an edgeedge with one O(15)NbCo3 trigonal pyramid, and  an edgeedge with one O(7)NbCo3 trigonal pyramid. In the fourteenth O site, O(14) is bonded to one Nb(3), one Co(4), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(2)Nb2Co2 trigonal pyramid,  an edgeedge with one O(13)NbCo3 trigonal pyramid,  an edgeedge with one O(15)NbCo3 trigonal pyramid, and  an edgeedge with one O(8)NbCo3 trigonal pyramid. In the fifteenth O site, O(15) is bonded to one Nb(3), one Co(4), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids,  an edgeedge with one O(3)Nb2Co2 trigonal pyramid,  an edgeedge with one O(13)NbCo3 trigonal pyramid,  an edgeedge with one O(14)NbCo3 trigonal pyramid, and  an edgeedge with one O(9)NbCo3 trigonal pyramid. In the sixteenth O site, O(16) is bonded to one Nb(4), one Co(1), one Co(2), and one Co(8) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(2)Nb2Co2 trigonal pyramid,  an edgeedge with one O(10)NbCo3 trigonal pyramid,  an edgeedge with one O(17)NbCo3 trigonal pyramid, and  an edgeedge with one O(18)NbCo3 trigonal pyramid. In the seventeenth O site, O(17) is bonded to one Nb(4), one Co(1), one Co(2), and one Co(8) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(1)Nb2Co2 trigonal pyramid,  an edgeedge with one O(11)NbCo3 trigonal pyramid,  an edgeedge with one O(16)NbCo3 trigonal pyramid, and  an edgeedge with one O(18)NbCo3 trigonal pyramid. In the eighteenth O site, O(18) is bonded to one Nb(4), one Co(1), one Co(2), and one Co(8) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids,  an edgeedge with one O(3)Nb2Co2 trigonal pyramid,  an edgeedge with one O(12)NbCo3 trigonal pyramid,  an edgeedge with one O(16)NbCo3 trigonal pyramid, and  an edgeedge with one O(17)NbCo3 trigonal pyramid. is represented by the CIF file [CIF]
data_Nb2Co4O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.215
_cell_length_b   5.226
_cell_length_c   14.319
_cell_angle_alpha   89.951
_cell_angle_beta   89.647
_cell_angle_gamma   59.956
_symmetry_Int_Tables_number   1
_cell_volume   337.836
_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
  Nb  Nb0  1  0.997  0.001  0.642  1.0
  Nb  Nb1  1  0.003  0.001  0.858  1.0
  Nb  Nb2  1  0.002  0.997  0.359  1.0
  Nb  Nb3  1  0.998  0.002  0.143  1.0
  Co  Co4  1  0.335  0.335  0.015  1.0
  Co  Co5  1  0.669  0.666  0.985  1.0
  Co  Co6  1  0.666  0.667  0.694  1.0
  Co  Co7  1  0.331  0.334  0.305  1.0
  Co  Co8  1  0.666  0.668  0.488  1.0
  Co  Co9  1  0.333  0.333  0.514  1.0
  Co  Co10  1  0.329  0.336  0.810  1.0
  Co  Co11  1  0.663  0.663  0.188  1.0
  O  O12  1  0.711  0.291  0.250  1.0
  O  O13  1  0.997  0.711  0.249  1.0
  O  O14  1  0.291  0.999  0.250  1.0
  O  O15  1  0.288  0.709  0.749  1.0
  O  O16  1  0.001  0.288  0.749  1.0
  O  O17  1  0.705  0.003  0.751  1.0
  O  O18  1  0.343  0.978  0.584  1.0
  O  O19  1  0.678  0.343  0.583  1.0
  O  O20  1  0.977  0.678  0.584  1.0
  O  O21  1  0.322  0.021  0.917  1.0
  O  O22  1  0.026  0.654  0.915  1.0
  O  O23  1  0.659  0.322  0.916  1.0
  O  O24  1  0.658  0.020  0.417  1.0
  O  O25  1  0.324  0.655  0.416  1.0
  O  O26  1  0.022  0.321  0.416  1.0
  O  O27  1  0.680  0.980  0.084  1.0
  O  O28  1  0.979  0.343  0.083  1.0
  O  O29  1  0.346  0.679  0.084  1.0
[/CIF]
.
The structure described by Co4Nb2O9 is Ilmenite-like structured and crystallizes in the triclinic P1 space group. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form distorted NbO6 octahedra that share corners with three equivalent Co(5)O6 octahedra, corners with three equivalent Co(6)O6 octahedra, corners with three equivalent Co(7)O6 octahedra, edges with three equivalent Co(3)O6 octahedra, and  a faceface with one Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-57°. In the second Nb site, Nb(2) is bonded to one O(10), one O(11), one O(12), one O(4), one O(5), and one O(6) atom to form distorted NbO6 octahedra that share corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Co(2)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, edges with three equivalent Co(7)O6 octahedra, and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the third Nb site, Nb(3) is bonded to one O(1), one O(13), one O(14), one O(15), one O(2), and one O(3) atom to form distorted NbO6 octahedra that share corners with three equivalent Co(5)O6 octahedra, corners with three equivalent Co(6)O6 octahedra, corners with three equivalent Co(8)O6 octahedra, edges with three equivalent Co(4)O6 octahedra, and  a faceface with one Nb(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-57°. In the fourth Nb site, Nb(4) is bonded to one O(1), one O(16), one O(17), one O(18), one O(2), and one O(3) atom to form distorted NbO6 octahedra that share corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Co(2)O6 octahedra, corners with three equivalent Co(4)O6 octahedra, edges with three equivalent Co(8)O6 octahedra, and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. There are eight inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(10), one O(11), one O(12), one O(16), one O(17), and one O(18) atom to form CoO6 octahedra that share corners with three equivalent Nb(2)O6 octahedra, corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Co(8)O6 octahedra, edges with three equivalent Co(2)O6 octahedra, and  a faceface with one Co(7)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the second Co site, Co(2) is bonded to one O(10), one O(11), one O(12), one O(16), one O(17), and one O(18) atom to form CoO6 octahedra that share corners with three equivalent Nb(2)O6 octahedra, corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Co(7)O6 octahedra, edges with three equivalent Co(1)O6 octahedra, and  a faceface with one Co(8)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the third Co site, Co(3) is bonded to one O(4), one O(5), one O(6), one O(7), one O(8), and one O(9) atom to form distorted CoO6 octahedra that share corners with three equivalent Nb(2)O6 octahedra, corners with three equivalent Co(6)O6 octahedra, corners with three equivalent Co(7)O6 octahedra, edges with three equivalent Nb(1)O6 octahedra, and  a faceface with one Co(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-66°. In the fourth Co site, Co(4) is bonded to one O(1), one O(13), one O(14), one O(15), one O(2), and one O(3) atom to form distorted CoO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Co(5)O6 octahedra, corners with three equivalent Co(8)O6 octahedra, edges with three equivalent Nb(3)O6 octahedra, and  a faceface with one Co(6)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-66°. In the fifth Co site, Co(5) is bonded to one O(13), one O(14), one O(15), one O(7), one O(8), and one O(9) atom to form CoO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, corners with three equivalent Co(4)O6 octahedra, edges with three equivalent Co(6)O6 octahedra, and  a faceface with one Co(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-57°. In the sixth Co site, Co(6) is bonded to one O(13), one O(14), one O(15), one O(7), one O(8), and one O(9) atom to form CoO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, edges with three equivalent Co(5)O6 octahedra, and  a faceface with one Co(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-57°. In the seventh Co site, Co(7) is bonded to one O(10), one O(11), one O(12), one O(4), one O(5), and one O(6) atom to form distorted CoO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Co(2)O6 octahedra, corners with three equivalent Co(3)O6 octahedra, edges with three equivalent Nb(2)O6 octahedra, and  a faceface with one Co(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-66°. In the eighth Co site, Co(8) is bonded to one O(1), one O(16), one O(17), one O(18), one O(2), and one O(3) atom to form distorted CoO6 octahedra that share corners with three equivalent Nb(3)O6 octahedra, corners with three equivalent Co(1)O6 octahedra, corners with three equivalent Co(4)O6 octahedra, edges with three equivalent Nb(4)O6 octahedra, and  a faceface with one Co(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-66°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded to one Nb(3), one Nb(4), one Co(4), and one Co(8) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(2)Nb2Co2 trigonal pyramid,  an edgeedge with one O(3)Nb2Co2 trigonal pyramid,  an edgeedge with one O(13)NbCo3 trigonal pyramid, and  an edgeedge with one O(17)NbCo3 trigonal pyramid. In the second O site, O(2) is bonded to one Nb(3), one Nb(4), one Co(4), and one Co(8) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(1)Nb2Co2 trigonal pyramid,  an edgeedge with one O(3)Nb2Co2 trigonal pyramid,  an edgeedge with one O(14)NbCo3 trigonal pyramid, and  an edgeedge with one O(16)NbCo3 trigonal pyramid. In the third O site, O(3) is bonded to one Nb(3), one Nb(4), one Co(4), and one Co(8) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids,  an edgeedge with one O(1)Nb2Co2 trigonal pyramid,  an edgeedge with one O(2)Nb2Co2 trigonal pyramid,  an edgeedge with one O(15)NbCo3 trigonal pyramid, and  an edgeedge with one O(18)NbCo3 trigonal pyramid. In the fourth O site, O(4) is bonded to one Nb(1), one Nb(2), one Co(3), and one Co(7) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(5)Nb2Co2 trigonal pyramid,  an edgeedge with one O(6)Nb2Co2 trigonal pyramid,  an edgeedge with one O(11)NbCo3 trigonal pyramid, and  an edgeedge with one O(7)NbCo3 trigonal pyramid. In the fifth O site, O(5) is bonded to one Nb(1), one Nb(2), one Co(3), and one Co(7) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(4)Nb2Co2 trigonal pyramid,  an edgeedge with one O(6)Nb2Co2 trigonal pyramid,  an edgeedge with one O(10)NbCo3 trigonal pyramid, and  an edgeedge with one O(8)NbCo3 trigonal pyramid. In the sixth O site, O(6) is bonded to one Nb(1), one Nb(2), one Co(3), and one Co(7) atom to form distorted ONb2Co2 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids,  an edgeedge with one O(4)Nb2Co2 trigonal pyramid,  an edgeedge with one O(5)Nb2Co2 trigonal pyramid,  an edgeedge with one O(12)NbCo3 trigonal pyramid, and  an edgeedge with one O(9)NbCo3 trigonal pyramid. In the seventh O site, O(7) is bonded to one Nb(1), one Co(3), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(4)Nb2Co2 trigonal pyramid,  an edgeedge with one O(13)NbCo3 trigonal pyramid,  an edgeedge with one O(8)NbCo3 trigonal pyramid, and  an edgeedge with one O(9)NbCo3 trigonal pyramid. In the eighth O site, O(8) is bonded to one Nb(1), one Co(3), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(5)Nb2Co2 trigonal pyramid,  an edgeedge with one O(14)NbCo3 trigonal pyramid,  an edgeedge with one O(7)NbCo3 trigonal pyramid, and  an edgeedge with one O(9)NbCo3 trigonal pyramid. In the ninth O site, O(9) is bonded to one Nb(1), one Co(3), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids,  an edgeedge with one O(6)Nb2Co2 trigonal pyramid,  an edgeedge with one O(15)NbCo3 trigonal pyramid,  an edgeedge with one O(7)NbCo3 trigonal pyramid, and  an edgeedge with one O(8)NbCo3 trigonal pyramid. In the tenth O site, O(10) is bonded to one Nb(2), one Co(1), one Co(2), and one Co(7) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(5)Nb2Co2 trigonal pyramid,  an edgeedge with one O(11)NbCo3 trigonal pyramid,  an edgeedge with one O(12)NbCo3 trigonal pyramid, and  an edgeedge with one O(16)NbCo3 trigonal pyramid. In the eleventh O site, O(11) is bonded to one Nb(2), one Co(1), one Co(2), and one Co(7) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(6)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(4)Nb2Co2 trigonal pyramid,  an edgeedge with one O(10)NbCo3 trigonal pyramid,  an edgeedge with one O(12)NbCo3 trigonal pyramid, and  an edgeedge with one O(17)NbCo3 trigonal pyramid. In the twelfth O site, O(12) is bonded to one Nb(2), one Co(1), one Co(2), and one Co(7) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(4)Nb2Co2 trigonal pyramids, corners with two equivalent O(5)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids,  an edgeedge with one O(6)Nb2Co2 trigonal pyramid,  an edgeedge with one O(10)NbCo3 trigonal pyramid,  an edgeedge with one O(11)NbCo3 trigonal pyramid, and  an edgeedge with one O(18)NbCo3 trigonal pyramid. In the thirteenth O site, O(13) is bonded to one Nb(3), one Co(4), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(1)Nb2Co2 trigonal pyramid,  an edgeedge with one O(14)NbCo3 trigonal pyramid,  an edgeedge with one O(15)NbCo3 trigonal pyramid, and  an edgeedge with one O(7)NbCo3 trigonal pyramid. In the fourteenth O site, O(14) is bonded to one Nb(3), one Co(4), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(15)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(9)NbCo3 trigonal pyramids,  an edgeedge with one O(2)Nb2Co2 trigonal pyramid,  an edgeedge with one O(13)NbCo3 trigonal pyramid,  an edgeedge with one O(15)NbCo3 trigonal pyramid, and  an edgeedge with one O(8)NbCo3 trigonal pyramid. In the fifteenth O site, O(15) is bonded to one Nb(3), one Co(4), one Co(5), and one Co(6) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(13)NbCo3 trigonal pyramids, corners with two equivalent O(14)NbCo3 trigonal pyramids, corners with two equivalent O(7)NbCo3 trigonal pyramids, corners with two equivalent O(8)NbCo3 trigonal pyramids,  an edgeedge with one O(3)Nb2Co2 trigonal pyramid,  an edgeedge with one O(13)NbCo3 trigonal pyramid,  an edgeedge with one O(14)NbCo3 trigonal pyramid, and  an edgeedge with one O(9)NbCo3 trigonal pyramid. In the sixteenth O site, O(16) is bonded to one Nb(4), one Co(1), one Co(2), and one Co(8) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(2)Nb2Co2 trigonal pyramid,  an edgeedge with one O(10)NbCo3 trigonal pyramid,  an edgeedge with one O(17)NbCo3 trigonal pyramid, and  an edgeedge with one O(18)NbCo3 trigonal pyramid. In the seventeenth O site, O(17) is bonded to one Nb(4), one Co(1), one Co(2), and one Co(8) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(3)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(12)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(18)NbCo3 trigonal pyramids,  an edgeedge with one O(1)Nb2Co2 trigonal pyramid,  an edgeedge with one O(11)NbCo3 trigonal pyramid,  an edgeedge with one O(16)NbCo3 trigonal pyramid, and  an edgeedge with one O(18)NbCo3 trigonal pyramid. In the eighteenth O site, O(18) is bonded to one Nb(4), one Co(1), one Co(2), and one Co(8) atom to form distorted ONbCo3 trigonal pyramids that share corners with two equivalent O(1)Nb2Co2 trigonal pyramids, corners with two equivalent O(2)Nb2Co2 trigonal pyramids, corners with two equivalent O(10)NbCo3 trigonal pyramids, corners with two equivalent O(11)NbCo3 trigonal pyramids, corners with two equivalent O(16)NbCo3 trigonal pyramids, corners with two equivalent O(17)NbCo3 trigonal pyramids,  an edgeedge with one O(3)Nb2Co2 trigonal pyramid,  an edgeedge with one O(12)NbCo3 trigonal pyramid,  an edgeedge with one O(16)NbCo3 trigonal pyramid, and  an edgeedge with one O(17)NbCo3 trigonal pyramid. is represented by the CIF file [CIF]
data_Nb2Co4O9
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.215
_cell_length_b   5.226
_cell_length_c   14.319
_cell_angle_alpha   89.951
_cell_angle_beta   89.647
_cell_angle_gamma   59.956
_symmetry_Int_Tables_number   1
_cell_volume   337.836
_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
  Nb  Nb0  1  0.997  0.001  0.642  1.0
  Nb  Nb1  1  0.003  0.001  0.858  1.0
  Nb  Nb2  1  0.002  0.997  0.359  1.0
  Nb  Nb3  1  0.998  0.002  0.143  1.0
  Co  Co4  1  0.335  0.335  0.015  1.0
  Co  Co5  1  0.669  0.666  0.985  1.0
  Co  Co6  1  0.666  0.667  0.694  1.0
  Co  Co7  1  0.331  0.334  0.305  1.0
  Co  Co8  1  0.666  0.668  0.488  1.0
  Co  Co9  1  0.333  0.333  0.514  1.0
  Co  Co10  1  0.329  0.336  0.810  1.0
  Co  Co11  1  0.663  0.663  0.188  1.0
  O  O12  1  0.711  0.291  0.250  1.0
  O  O13  1  0.997  0.711  0.249  1.0
  O  O14  1  0.291  0.999  0.250  1.0
  O  O15  1  0.288  0.709  0.749  1.0
  O  O16  1  0.001  0.288  0.749  1.0
  O  O17  1  0.705  0.003  0.751  1.0
  O  O18  1  0.343  0.978  0.584  1.0
  O  O19  1  0.678  0.343  0.583  1.0
  O  O20  1  0.977  0.678  0.584  1.0
  O  O21  1  0.322  0.021  0.917  1.0
  O  O22  1  0.026  0.654  0.915  1.0
  O  O23  1  0.659  0.322  0.916  1.0
  O  O24  1  0.658  0.020  0.417  1.0
  O  O25  1  0.324  0.655  0.416  1.0
  O  O26  1  0.022  0.321  0.416  1.0
  O  O27  1  0.680  0.980  0.084  1.0
  O  O28  1  0.979  0.343  0.083  1.0
  O  O29  1  0.346  0.679  0.084  1.0
[/CIF]
.