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  a cornercorner with one Nb(3)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids,  a cornercorner with one Mn(3)O4 trigonal pyramid,  an edgeedge with one Nb(3)O6 octahedra,  an edgeedge with one Nb(4)O6 octahedra, and  an edgeedge with one Mn(3)O4 trigonal pyramid. The corner-sharing octahedral tilt angles are 42°. 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, corners with three equivalent Mn(1)O5 trigonal bipyramids, and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-49°. 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  a cornercorner with one Mg(1)O5 trigonal bipyramid,  a cornercorner with one Mn(1)O5 trigonal bipyramid,  a cornercorner with one Mn(3)O4 trigonal pyramid,  an edgeedge with one Mg(1)O5 trigonal bipyramid, edges with two equivalent Mn(1)O5 trigonal bipyramids, and  a faceface with one Nb(1)O6 octahedra. In the fourth Nb site, Nb(4) 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 NbO6 octahedra that share corners with three equivalent Mn(3)O4 trigonal pyramids and  an edgeedge with one Mg(1)O5 trigonal bipyramid. There are six inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(10), one O(11), one O(12), one O(18), and one O(7) atom to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Nb(3)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-68°. 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(16), one O(17), one O(6), and one O(9) atom to form distorted MnO4 trigonal pyramids that share  a cornercorner with one Nb(3)O6 octahedra, corners with three equivalent Nb(4)O6 octahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 59-68°. In the fourth Mn site, Mn(4) is bonded in a 5-coordinate geometry to one O(10), one O(12), one O(16), one O(17), and one O(9) atom. 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 distorted MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-49°. 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 T-shaped geometry to one Nb(2), one Nb(4), and one Mn(6) atom. In the fourth O site, O(4) is bonded in a T-shaped geometry to 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 Mg(1), one Nb(3), and one Mn(3) 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 to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom to form a mixture of distorted corner and edge-sharing OMgMn2Nb tetrahedra. In the tenth O site, O(10) is bonded to one Mg(1), one Nb(3), one Mn(1), and one Mn(4) atom to form a mixture of distorted corner and edge-sharing OMgMn2Nb tetrahedra. 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 Mg(1), one Nb(3), one Mn(1), and one Mn(4) atom. In the thirteenth O site, O(13) is bonded in a distorted T-shaped geometry to 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 trigonal planar geometry to one Nb(4), one Mn(3), and one Mn(4) atom. In the seventeenth O site, O(17) is bonded to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom to form a mixture of corner and edge-sharing OMgMn2Nb trigonal pyramids. In the eighteenth O site, O(18) is bonded in a distorted T-shaped 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(10), one O(12), one O(17), one O(6), and one O(9) atom to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Nb(3)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids,  a cornercorner with one Mn(3)O4 trigonal pyramid,  an edgeedge with one Nb(3)O6 octahedra,  an edgeedge with one Nb(4)O6 octahedra, and  an edgeedge with one Mn(3)O4 trigonal pyramid. The corner-sharing octahedral tilt angles are 42°. The Mg(1)-O(10) bond length is 2.22 Å. The Mg(1)-O(12) bond length is 2.02 Å. The Mg(1)-O(17) bond length is 2.17 Å. The Mg(1)-O(6) bond length is 2.02 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, corners with three equivalent Mn(1)O5 trigonal bipyramids, and  a faceface with one Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-49°. The Nb(1)-O(11) bond length is 2.16 Å. The Nb(1)-O(14) bond length is 1.89 Å. The Nb(1)-O(18) bond length is 2.31 Å. The Nb(1)-O(2) bond length is 1.91 Å. The Nb(1)-O(7) bond length is 2.27 Å. The Nb(1)-O(8) bond length is 1.89 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 1.94 Å. The Nb(2)-O(13) bond length is 2.29 Å. The Nb(2)-O(15) bond length is 1.99 Å. The Nb(2)-O(3) bond length is 2.22 Å. The Nb(2)-O(4) bond length is 2.06 Å. The Nb(2)-O(5) bond length is 1.91 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  a cornercorner with one Mg(1)O5 trigonal bipyramid,  a cornercorner with one Mn(1)O5 trigonal bipyramid,  a cornercorner with one Mn(3)O4 trigonal pyramid,  an edgeedge with one Mg(1)O5 trigonal bipyramid, edges with two equivalent Mn(1)O5 trigonal bipyramids, and  a faceface with one Nb(1)O6 octahedra. The Nb(3)-O(10) bond length is 2.03 Å. The Nb(3)-O(11) bond length is 2.14 Å. The Nb(3)-O(12) bond length is 2.17 Å. The Nb(3)-O(18) bond length is 1.95 Å. The Nb(3)-O(6) bond length is 1.94 Å. The Nb(3)-O(7) bond length is 1.95 Å. In the fourth Nb site, Nb(4) 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 NbO6 octahedra that share corners with three equivalent Mn(3)O4 trigonal pyramids and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The Nb(4)-O(13) bond length is 1.96 Å. The Nb(4)-O(16) bond length is 1.94 Å. The Nb(4)-O(17) bond length is 2.06 Å. The Nb(4)-O(3) bond length is 2.10 Å. The Nb(4)-O(4) bond length is 2.06 Å. The Nb(4)-O(9) bond length is 2.01 Å. There are six inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(10), one O(11), one O(12), one O(18), and one O(7) atom to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Nb(3)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent Nb(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-68°. The Mn(1)-O(10) bond length is 2.04 Å. The Mn(1)-O(11) bond length is 1.90 Å. The Mn(1)-O(12) bond length is 2.02 Å. The Mn(1)-O(18) bond length is 2.02 Å. The Mn(1)-O(7) bond length is 2.03 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 2.32 Å. The Mn(2)-O(14) bond length is 2.09 Å. The Mn(2)-O(15) bond length is 2.60 Å. The Mn(2)-O(2) bond length is 2.09 Å. The Mn(2)-O(5) bond length is 2.28 Å. The Mn(2)-O(8) bond length is 2.10 Å. In the third Mn site, Mn(3) is bonded to one O(16), one O(17), one O(6), and one O(9) atom to form distorted MnO4 trigonal pyramids that share  a cornercorner with one Nb(3)O6 octahedra, corners with three equivalent Nb(4)O6 octahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 59-68°. The Mn(3)-O(16) bond length is 2.02 Å. The Mn(3)-O(17) bond length is 2.09 Å. The Mn(3)-O(6) bond length is 2.21 Å. The Mn(3)-O(9) bond length is 2.04 Å. In the fourth Mn site, Mn(4) is bonded in a 5-coordinate geometry to one O(10), one O(12), one O(16), one O(17), and one O(9) atom. The Mn(4)-O(10) bond length is 2.07 Å. The Mn(4)-O(12) bond length is 2.34 Å. The Mn(4)-O(16) bond length is 2.04 Å. The Mn(4)-O(17) bond length is 2.06 Å. The Mn(4)-O(9) bond length is 2.32 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 distorted MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-49°. The Mn(5)-O(1) bond length is 2.72 Å. The Mn(5)-O(14) bond length is 2.15 Å. The Mn(5)-O(15) bond length is 2.23 Å. The Mn(5)-O(2) bond length is 2.13 Å. The Mn(5)-O(5) bond length is 2.23 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 2.04 Å. The Mn(6)-O(13) bond length is 2.02 Å. The Mn(6)-O(15) bond length is 2.03 Å. The Mn(6)-O(3) bond length is 1.90 Å. The Mn(6)-O(4) bond length is 2.11 Å. The Mn(6)-O(5) bond length is 2.45 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 T-shaped geometry to one Nb(2), one Nb(4), and one Mn(6) atom. In the fourth O site, O(4) is bonded in a T-shaped geometry to 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 Mg(1), one Nb(3), and one Mn(3) 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 to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom to form a mixture of distorted corner and edge-sharing OMgMn2Nb tetrahedra. In the tenth O site, O(10) is bonded to one Mg(1), one Nb(3), one Mn(1), and one Mn(4) atom to form a mixture of distorted corner and edge-sharing OMgMn2Nb tetrahedra. 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 Mg(1), one Nb(3), one Mn(1), and one Mn(4) atom. In the thirteenth O site, O(13) is bonded in a distorted T-shaped geometry to 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 trigonal planar geometry to one Nb(4), one Mn(3), and one Mn(4) atom. In the seventeenth O site, O(17) is bonded to one Mg(1), one Nb(4), one Mn(3), and one Mn(4) atom to form a mixture of corner and edge-sharing OMgMn2Nb trigonal pyramids. In the eighteenth O site, O(18) is bonded in a distorted T-shaped geometry to one Nb(1), one Nb(3), and one Mn(1) atom.