The crystal structure described by MgNb4Mn6O18 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(12), one O(17), one O(6), and one O(9) atom to form distorted MgO5 trigonal bipyramids that share corners with three equivalent Nb(3)O6 octahedra, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mn(3)O6 octahedra, and  an edgeedge with one Mn(4)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 46-57°. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(11), one O(14), one O(18), one O(2), one O(7), and one O(8) atom to form distorted NbO6 octahedra that share corners with three equivalent Mn(2)O6 octahedra, corners with three equivalent Mn(5)O6 octahedra, corners with two equivalent Mn(1)O4 trigonal pyramids,  an edgeedge with one Mn(1)O4 trigonal pyramid, and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-56°. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(1), one O(13), one O(15), one O(3), one O(4), and one O(5) atom. In the third Nb site, Nb(3) is bonded to one O(10), one O(11), one O(12), one O(18), one O(6), and one O(7) atom to form distorted NbO6 octahedra that share corners with three equivalent Mg(1)O5 trigonal bipyramids, corners with three equivalent Mn(4)O5 trigonal bipyramids, corners with three equivalent Mn(1)O4 trigonal pyramids, and  a faceface with one Nb(1)O6 octahedra. In the fourth Nb site, Nb(4) is bonded in a 6-coordinate geometry to one O(13), one O(16), one O(17), one O(3), one O(4), and one O(9) atom. There are six inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(11), one O(18), one O(7), and one O(8) atom to form distorted MnO4 trigonal pyramids that share  a cornercorner with one Mn(2)O6 octahedra,  a cornercorner with one Mn(5)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, and  an edgeedge with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 45-88°. In the second Mn site, Mn(2) is bonded to one O(1), one O(14), one O(15), one O(2), one O(5), and one O(8) atom to form distorted MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra,  a cornercorner with one Mn(1)O4 trigonal pyramid, edges with three equivalent Mn(5)O6 octahedra, and  a faceface with one Mn(6)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-54°. In the third Mn site, Mn(3) is bonded to one O(13), one O(16), one O(17), one O(3), one O(4), and one O(9) atom to form distorted MnO6 octahedra that share corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mg(1)O5 trigonal bipyramid, and  a faceface with one Mn(6)O6 octahedra. In the fourth Mn site, Mn(4) is bonded to one O(10), one O(12), one O(16), one O(6), and one O(9) atom to form MnO5 trigonal bipyramids that share corners with two equivalent Mn(3)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 48-58°. In the fifth Mn site, Mn(5) is bonded to one O(1), one O(14), one O(15), one O(2), one O(5), and one O(8) atom to form MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Mn(6)O6 octahedra,  a cornercorner with one Mn(1)O4 trigonal pyramid, and edges with three equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-56°. In the sixth Mn site, Mn(6) is bonded to one O(1), one O(13), one O(15), one O(3), one O(4), and one O(5) atom to form a mixture of distorted face and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 50-53°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded to one Nb(2), one Mn(2), one Mn(5), and one Mn(6) atom to form distorted corner-sharing OMn3Nb trigonal pyramids. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Nb(1), one Mn(2), and one Mn(5) atom. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Nb(2), one Nb(4), one Mn(3), and one Mn(6) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Nb(2), one Nb(4), one Mn(3), and one Mn(6) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Nb(2), one Mn(2), one Mn(5), and one Mn(6) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Mg(1), one Nb(3), and one Mn(4) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Nb(1), one Nb(3), and one Mn(1) atom. In the eighth O site, O(8) is bonded to one Nb(1), one Mn(1), one Mn(2), and one Mn(5) atom to form distorted corner-sharing OMn3Nb trigonal pyramids. In the ninth O site, O(9) is bonded in a distorted trigonal pyramidal geometry to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom. In the tenth O site, O(10) is bonded in a trigonal planar geometry to one Mg(1), one Nb(3), and one Mn(4) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(3), and one Mn(1) atom. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to one Mg(1), one Nb(3), and one Mn(4) atom. In the thirteenth O site, O(13) is bonded in a distorted rectangular see-saw-like geometry to one Nb(2), one Nb(4), one Mn(3), and one Mn(6) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal planar geometry to one Nb(1), one Mn(2), and one Mn(5) atom. In the fifteenth O site, O(15) is bonded in a 4-coordinate geometry to one Nb(2), one Mn(2), one Mn(5), and one Mn(6) atom. In the sixteenth O site, O(16) is bonded in a distorted trigonal planar geometry to one Nb(4), one Mn(3), and one Mn(4) atom. In the seventeenth O site, O(17) is bonded in a distorted T-shaped geometry to one Mg(1), one Nb(4), and one Mn(3) atom. In the eighteenth O site, O(18) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(3), and one Mn(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_MgMn6Nb4O18
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.248
_cell_length_b   5.568
_cell_length_c   15.028
_cell_angle_alpha   85.050
_cell_angle_beta   93.647
_cell_angle_gamma   120.746
_symmetry_Int_Tables_number   1
_cell_volume   375.882
_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
  Mg  Mg0  1  0.659  0.386  0.535  1.0
  Mn  Mn1  1  0.706  0.336  0.778  1.0
  Mn  Mn2  1  0.654  0.317  0.982  1.0
  Mn  Mn3  1  0.700  0.348  0.347  1.0
  Mn  Mn4  1  0.335  0.723  0.524  1.0
  Mn  Mn5  1  0.333  0.660  0.005  1.0
  Mn  Mn6  1  0.667  0.306  0.170  1.0
  Nb  Nb7  1  0.972  0.980  0.859  1.0
  Nb  Nb8  1  0.997  0.963  0.153  1.0
  Nb  Nb9  1  0.006  0.026  0.649  1.0
  Nb  Nb10  1  0.999  0.000  0.362  1.0
  O  O11  1  0.351  0.297  0.090  1.0
  O  O12  1  0.658  0.675  0.926  1.0
  O  O13  1  0.935  0.229  0.248  1.0
  O  O14  1  0.342  0.079  0.249  1.0
  O  O15  1  0.977  0.645  0.096  1.0
  O  O16  1  0.689  0.710  0.591  1.0
  O  O17  1  0.722  0.027  0.750  1.0
  O  O18  1  0.952  0.306  0.897  1.0
  O  O19  1  0.978  0.674  0.431  1.0
  O  O20  1  0.323  0.036  0.591  1.0
  O  O21  1  0.306  0.241  0.756  1.0
  O  O22  1  0.994  0.335  0.587  1.0
  O  O23  1  0.789  0.698  0.256  1.0
  O  O24  1  0.291  0.979  0.929  1.0
  O  O25  1  0.702  0.016  0.085  1.0
  O  O26  1  0.693  0.001  0.419  1.0
  O  O27  1  0.339  0.285  0.420  1.0
  O  O28  1  0.938  0.725  0.763  1.0
[/CIF]
.
The crystal structure described by MgNb4Mn6O18 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(12), one O(17), one O(6), and one O(9) atom to form distorted MgO5 trigonal bipyramids that share corners with three equivalent Nb(3)O6 octahedra, corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mn(3)O6 octahedra, and  an edgeedge with one Mn(4)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 46-57°. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(11), one O(14), one O(18), one O(2), one O(7), and one O(8) atom to form distorted NbO6 octahedra that share corners with three equivalent Mn(2)O6 octahedra, corners with three equivalent Mn(5)O6 octahedra, corners with two equivalent Mn(1)O4 trigonal pyramids,  an edgeedge with one Mn(1)O4 trigonal pyramid, and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-56°. In the second Nb site, Nb(2) is bonded in a 6-coordinate geometry to one O(1), one O(13), one O(15), one O(3), one O(4), and one O(5) atom. In the third Nb site, Nb(3) is bonded to one O(10), one O(11), one O(12), one O(18), one O(6), and one O(7) atom to form distorted NbO6 octahedra that share corners with three equivalent Mg(1)O5 trigonal bipyramids, corners with three equivalent Mn(4)O5 trigonal bipyramids, corners with three equivalent Mn(1)O4 trigonal pyramids, and  a faceface with one Nb(1)O6 octahedra. In the fourth Nb site, Nb(4) is bonded in a 6-coordinate geometry to one O(13), one O(16), one O(17), one O(3), one O(4), and one O(9) atom. There are six inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(11), one O(18), one O(7), and one O(8) atom to form distorted MnO4 trigonal pyramids that share  a cornercorner with one Mn(2)O6 octahedra,  a cornercorner with one Mn(5)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, and  an edgeedge with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 45-88°. In the second Mn site, Mn(2) is bonded to one O(1), one O(14), one O(15), one O(2), one O(5), and one O(8) atom to form distorted MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra,  a cornercorner with one Mn(1)O4 trigonal pyramid, edges with three equivalent Mn(5)O6 octahedra, and  a faceface with one Mn(6)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-54°. In the third Mn site, Mn(3) is bonded to one O(13), one O(16), one O(17), one O(3), one O(4), and one O(9) atom to form distorted MnO6 octahedra that share corners with two equivalent Mn(4)O5 trigonal bipyramids,  an edgeedge with one Mg(1)O5 trigonal bipyramid, and  a faceface with one Mn(6)O6 octahedra. In the fourth Mn site, Mn(4) is bonded to one O(10), one O(12), one O(16), one O(6), and one O(9) atom to form MnO5 trigonal bipyramids that share corners with two equivalent Mn(3)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 48-58°. In the fifth Mn site, Mn(5) is bonded to one O(1), one O(14), one O(15), one O(2), one O(5), and one O(8) atom to form MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Mn(6)O6 octahedra,  a cornercorner with one Mn(1)O4 trigonal pyramid, and edges with three equivalent Mn(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-56°. In the sixth Mn site, Mn(6) is bonded to one O(1), one O(13), one O(15), one O(3), one O(4), and one O(5) atom to form a mixture of distorted face and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 50-53°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded to one Nb(2), one Mn(2), one Mn(5), and one Mn(6) atom to form distorted corner-sharing OMn3Nb trigonal pyramids. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Nb(1), one Mn(2), and one Mn(5) atom. In the third O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Nb(2), one Nb(4), one Mn(3), and one Mn(6) atom. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Nb(2), one Nb(4), one Mn(3), and one Mn(6) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Nb(2), one Mn(2), one Mn(5), and one Mn(6) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Mg(1), one Nb(3), and one Mn(4) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Nb(1), one Nb(3), and one Mn(1) atom. In the eighth O site, O(8) is bonded to one Nb(1), one Mn(1), one Mn(2), and one Mn(5) atom to form distorted corner-sharing OMn3Nb trigonal pyramids. In the ninth O site, O(9) is bonded in a distorted trigonal pyramidal geometry to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom. In the tenth O site, O(10) is bonded in a trigonal planar geometry to one Mg(1), one Nb(3), and one Mn(4) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(3), and one Mn(1) atom. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to one Mg(1), one Nb(3), and one Mn(4) atom. In the thirteenth O site, O(13) is bonded in a distorted rectangular see-saw-like geometry to one Nb(2), one Nb(4), one Mn(3), and one Mn(6) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal planar geometry to one Nb(1), one Mn(2), and one Mn(5) atom. In the fifteenth O site, O(15) is bonded in a 4-coordinate geometry to one Nb(2), one Mn(2), one Mn(5), and one Mn(6) atom. In the sixteenth O site, O(16) is bonded in a distorted trigonal planar geometry to one Nb(4), one Mn(3), and one Mn(4) atom. In the seventeenth O site, O(17) is bonded in a distorted T-shaped geometry to one Mg(1), one Nb(4), and one Mn(3) atom. In the eighteenth O site, O(18) is bonded in a distorted trigonal planar geometry to one Nb(1), one Nb(3), and one Mn(1) atom. is represented by the Crystallographic Information File (CIF) [CIF]
data_MgMn6Nb4O18
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.248
_cell_length_b   5.568
_cell_length_c   15.028
_cell_angle_alpha   85.050
_cell_angle_beta   93.647
_cell_angle_gamma   120.746
_symmetry_Int_Tables_number   1
_cell_volume   375.882
_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
  Mg  Mg0  1  0.659  0.386  0.535  1.0
  Mn  Mn1  1  0.706  0.336  0.778  1.0
  Mn  Mn2  1  0.654  0.317  0.982  1.0
  Mn  Mn3  1  0.700  0.348  0.347  1.0
  Mn  Mn4  1  0.335  0.723  0.524  1.0
  Mn  Mn5  1  0.333  0.660  0.005  1.0
  Mn  Mn6  1  0.667  0.306  0.170  1.0
  Nb  Nb7  1  0.972  0.980  0.859  1.0
  Nb  Nb8  1  0.997  0.963  0.153  1.0
  Nb  Nb9  1  0.006  0.026  0.649  1.0
  Nb  Nb10  1  0.999  0.000  0.362  1.0
  O  O11  1  0.351  0.297  0.090  1.0
  O  O12  1  0.658  0.675  0.926  1.0
  O  O13  1  0.935  0.229  0.248  1.0
  O  O14  1  0.342  0.079  0.249  1.0
  O  O15  1  0.977  0.645  0.096  1.0
  O  O16  1  0.689  0.710  0.591  1.0
  O  O17  1  0.722  0.027  0.750  1.0
  O  O18  1  0.952  0.306  0.897  1.0
  O  O19  1  0.978  0.674  0.431  1.0
  O  O20  1  0.323  0.036  0.591  1.0
  O  O21  1  0.306  0.241  0.756  1.0
  O  O22  1  0.994  0.335  0.587  1.0
  O  O23  1  0.789  0.698  0.256  1.0
  O  O24  1  0.291  0.979  0.929  1.0
  O  O25  1  0.702  0.016  0.085  1.0
  O  O26  1  0.693  0.001  0.419  1.0
  O  O27  1  0.339  0.285  0.420  1.0
  O  O28  1  0.938  0.725  0.763  1.0
[/CIF]
.