MgNb4Mn6O18 crystallizes in the triclinic P1 space group. Mg(1) 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 MgO6 octahedra that share corners with three equivalent Mn(4)O6 octahedra and  a faceface with one Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-53°. 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(5)O6 octahedra and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-47°. 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 Mn(3)O6 octahedra, corners with three equivalent Mn(4)O6 octahedra, and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-57°. 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 in a 4-coordinate geometry to one O(11), one O(12), one O(18), and one O(7) atom. In the second Mn site, Mn(2) is bonded in a 6-coordinate geometry to one O(1), one O(14), one O(15), one O(2), one O(5), and one O(8) atom. In the third Mn site, Mn(3) is bonded to one O(10), one O(12), one O(16), one O(17), one O(6), and one O(9) atom to form MnO6 octahedra that share corners with three equivalent Nb(3)O6 octahedra, edges with three equivalent Mn(4)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-51°. In the fourth Mn site, Mn(4) is bonded to one O(10), one O(12), one O(16), one O(17), one O(6), and one O(9) atom to form MnO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, and edges with three equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-57°. 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. The corner-sharing octahedral tilt angles range from 43-47°. In the sixth Mn site, Mn(6) 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. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Nb(2), one Mn(2), one Mn(5), and one Mn(6) atom. 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 Mg(1), one Nb(2), one Nb(4), and one Mn(6) atom. In the fourth O site, O(4) is bonded in a square co-planar geometry to one Mg(1), one Nb(2), one Nb(4), 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 3-coordinate geometry to one Nb(3), one Mn(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 in a distorted trigonal planar geometry to one Nb(1), one Mn(2), and one Mn(5) atom. In the ninth O site, O(9) is bonded in a 4-coordinate 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 3-coordinate geometry to one Nb(3), one Mn(3), and one Mn(4) atom. In the eleventh O site, O(11) is bonded in a distorted T-shaped 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 see-saw-like geometry to one Nb(3), one Mn(1), one Mn(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 Mg(1), one Nb(2), one Nb(4), 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 4-coordinate geometry to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom. In the seventeenth O site, O(17) is bonded in a 4-coordinate geometry to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom. In the eighteenth O site, O(18) is bonded in a distorted trigonal non-coplanar geometry to one Nb(1), one Nb(3), and one Mn(1) atom.
MgNb4Mn6O18 crystallizes in the triclinic P1 space group. Mg(1) 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 MgO6 octahedra that share corners with three equivalent Mn(4)O6 octahedra and  a faceface with one Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-53°. The Mg(1)-O(13) bond length is 2.04 Å. The Mg(1)-O(16) bond length is 2.10 Å. The Mg(1)-O(17) bond length is 2.10 Å. The Mg(1)-O(3) bond length is 2.12 Å. The Mg(1)-O(4) bond length is 2.13 Å. The Mg(1)-O(9) bond length is 2.10 Å. 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(5)O6 octahedra and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-47°. The Nb(1)-O(11) bond length is 2.15 Å. The Nb(1)-O(14) bond length is 1.90 Å. The Nb(1)-O(18) bond length is 2.19 Å. The Nb(1)-O(2) bond length is 1.91 Å. The Nb(1)-O(7) bond length is 2.18 Å. The Nb(1)-O(8) bond length is 1.91 Å. 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. The Nb(2)-O(1) bond length is 2.02 Å. The Nb(2)-O(13) bond length is 2.02 Å. The Nb(2)-O(15) bond length is 1.91 Å. The Nb(2)-O(3) bond length is 2.26 Å. The Nb(2)-O(4) bond length is 2.19 Å. The Nb(2)-O(5) bond length is 1.95 Å. 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 Mn(3)O6 octahedra, corners with three equivalent Mn(4)O6 octahedra, and  a faceface with one Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-57°. The Nb(3)-O(10) bond length is 1.93 Å. The Nb(3)-O(11) bond length is 2.20 Å. The Nb(3)-O(12) bond length is 2.04 Å. The Nb(3)-O(18) bond length is 2.00 Å. The Nb(3)-O(6) bond length is 1.94 Å. The Nb(3)-O(7) bond length is 2.10 Å. 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. The Nb(4)-O(13) bond length is 2.15 Å. The Nb(4)-O(16) bond length is 1.91 Å. The Nb(4)-O(17) bond length is 1.93 Å. The Nb(4)-O(3) bond length is 2.23 Å. The Nb(4)-O(4) bond length is 2.21 Å. The Nb(4)-O(9) bond length is 1.94 Å. There are six inequivalent Mn sites. In the first Mn site, Mn(1) is bonded in a 4-coordinate geometry to one O(11), one O(12), one O(18), and one O(7) atom. The Mn(1)-O(11) bond length is 1.88 Å. The Mn(1)-O(12) bond length is 2.14 Å. The Mn(1)-O(18) bond length is 1.92 Å. The Mn(1)-O(7) bond length is 1.86 Å. In the second Mn site, Mn(2) is bonded in a 6-coordinate geometry to one O(1), one O(14), one O(15), one O(2), one O(5), and one O(8) atom. The Mn(2)-O(1) bond length is 2.38 Å. The Mn(2)-O(14) bond length is 2.04 Å. The Mn(2)-O(15) bond length is 2.54 Å. The Mn(2)-O(2) bond length is 2.03 Å. The Mn(2)-O(5) bond length is 2.56 Å. The Mn(2)-O(8) bond length is 2.04 Å. In the third Mn site, Mn(3) is bonded to one O(10), one O(12), one O(16), one O(17), one O(6), and one O(9) atom to form MnO6 octahedra that share corners with three equivalent Nb(3)O6 octahedra, edges with three equivalent Mn(4)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-51°. The Mn(3)-O(10) bond length is 2.06 Å. The Mn(3)-O(12) bond length is 2.13 Å. The Mn(3)-O(16) bond length is 2.27 Å. The Mn(3)-O(17) bond length is 2.22 Å. The Mn(3)-O(6) bond length is 2.11 Å. The Mn(3)-O(9) bond length is 2.33 Å. In the fourth Mn site, Mn(4) is bonded to one O(10), one O(12), one O(16), one O(17), one O(6), and one O(9) atom to form MnO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Nb(3)O6 octahedra, and edges with three equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-57°. The Mn(4)-O(10) bond length is 2.15 Å. The Mn(4)-O(12) bond length is 2.34 Å. The Mn(4)-O(16) bond length is 2.48 Å. The Mn(4)-O(17) bond length is 2.45 Å. The Mn(4)-O(6) bond length is 2.12 Å. The Mn(4)-O(9) bond length is 2.26 Å. 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. The corner-sharing octahedral tilt angles range from 43-47°. The Mn(5)-O(1) bond length is 2.40 Å. The Mn(5)-O(14) bond length is 2.12 Å. The Mn(5)-O(15) bond length is 2.29 Å. The Mn(5)-O(2) bond length is 2.11 Å. The Mn(5)-O(5) bond length is 2.32 Å. The Mn(5)-O(8) bond length is 2.15 Å. In the sixth Mn site, Mn(6) 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. The Mn(6)-O(1) bond length is 1.93 Å. The Mn(6)-O(13) bond length is 2.40 Å. The Mn(6)-O(15) bond length is 2.12 Å. The Mn(6)-O(3) bond length is 1.96 Å. The Mn(6)-O(4) bond length is 1.96 Å. The Mn(6)-O(5) bond length is 2.05 Å. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Nb(2), one Mn(2), one Mn(5), and one Mn(6) atom. 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 Mg(1), one Nb(2), one Nb(4), and one Mn(6) atom. In the fourth O site, O(4) is bonded in a square co-planar geometry to one Mg(1), one Nb(2), one Nb(4), 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 3-coordinate geometry to one Nb(3), one Mn(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 in a distorted trigonal planar geometry to one Nb(1), one Mn(2), and one Mn(5) atom. In the ninth O site, O(9) is bonded in a 4-coordinate 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 3-coordinate geometry to one Nb(3), one Mn(3), and one Mn(4) atom. In the eleventh O site, O(11) is bonded in a distorted T-shaped 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 see-saw-like geometry to one Nb(3), one Mn(1), one Mn(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 Mg(1), one Nb(2), one Nb(4), 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 4-coordinate geometry to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom. In the seventeenth O site, O(17) is bonded in a 4-coordinate geometry to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom. In the eighteenth O site, O(18) is bonded in a distorted trigonal non-coplanar geometry to one Nb(1), one Nb(3), and one Mn(1) atom.