MgNb4Mn6O18 crystallizes in the trigonal P3 space group. Mg(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form distorted MgO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Mn(2)O6 octahedra, edges with three equivalent Nb(2)O6 pentagonal pyramids, and  a faceface with one Mn(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-47°. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to three equivalent O(2) and three equivalent O(5) atoms to form distorted NbO6 octahedra that share corners with three equivalent Mn(1)O6 octahedra, corners with three equivalent Mn(2)O6 octahedra, and corners with three equivalent Mn(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 33-50°. In the second Nb site, Nb(2) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form distorted NbO6 pentagonal pyramids that share corners with three equivalent Mn(2)O6 octahedra, corners with three equivalent Mn(5)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, and  a faceface with one Nb(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-56°. In the third Nb site, Nb(3) is bonded in a 6-coordinate geometry to three equivalent O(4) and three equivalent O(5) atoms. In the fourth Nb site, Nb(4) is bonded to three equivalent O(3) and three equivalent O(6) atoms to form distorted NbO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Mn(3)O6 octahedra, corners with three equivalent Mn(4)O6 octahedra, and  a faceface with one Nb(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 46-54°. There are six inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to three equivalent O(4) and three equivalent O(5) atoms to form distorted MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, 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 33-46°. In the second Mn site, Mn(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MnO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(2)O6 pentagonal pyramids, and edges with three equivalent Mn(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-48°. In the third Mn site, Mn(3) is bonded to three equivalent O(4) and three equivalent O(6) atoms to form distorted MnO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra, edges with three equivalent Mn(4)O6 octahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 54°. In the fourth Mn site, Mn(4) is bonded to three equivalent O(4) and three equivalent O(6) atoms to form MnO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra, and edges with three equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. In the fifth Mn site, Mn(5) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(2)O6 pentagonal pyramids, edges with three equivalent Mn(2)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. In the sixth Mn site, Mn(6) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(3) atoms. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), 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 to one Mg(1), one Nb(2), one Nb(4), and one Mn(6) atom to form a mixture of distorted corner and edge-sharing OMgMnNb2 trigonal pyramids. In the fourth O site, O(4) is bonded to one Nb(3), one Mn(1), one Mn(3), and one Mn(4) atom to form a mixture of distorted corner and edge-sharing OMn3Nb trigonal pyramids. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Nb(1), one Nb(3), and one Mn(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Nb(4), one Mn(3), and one Mn(4) atom.
MgNb4Mn6O18 crystallizes in the trigonal P3 space group. Mg(1) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form distorted MgO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Mn(2)O6 octahedra, edges with three equivalent Nb(2)O6 pentagonal pyramids, and  a faceface with one Mn(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-47°. All Mg(1)-O(1) bond lengths are 2.30 Å. All Mg(1)-O(3) bond lengths are 2.01 Å. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to three equivalent O(2) and three equivalent O(5) atoms to form distorted NbO6 octahedra that share corners with three equivalent Mn(1)O6 octahedra, corners with three equivalent Mn(2)O6 octahedra, and corners with three equivalent Mn(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 33-50°. All Nb(1)-O(2) bond lengths are 1.89 Å. All Nb(1)-O(5) bond lengths are 2.24 Å. In the second Nb site, Nb(2) is bonded to three equivalent O(1) and three equivalent O(3) atoms to form distorted NbO6 pentagonal pyramids that share corners with three equivalent Mn(2)O6 octahedra, corners with three equivalent Mn(5)O6 octahedra, edges with three equivalent Mg(1)O6 octahedra, and  a faceface with one Nb(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-56°. All Nb(2)-O(1) bond lengths are 1.95 Å. All Nb(2)-O(3) bond lengths are 2.15 Å. In the third Nb site, Nb(3) is bonded in a 6-coordinate geometry to three equivalent O(4) and three equivalent O(5) atoms. All Nb(3)-O(4) bond lengths are 2.00 Å. All Nb(3)-O(5) bond lengths are 2.08 Å. In the fourth Nb site, Nb(4) is bonded to three equivalent O(3) and three equivalent O(6) atoms to form distorted NbO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Mn(3)O6 octahedra, corners with three equivalent Mn(4)O6 octahedra, and  a faceface with one Nb(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 46-54°. All Nb(4)-O(3) bond lengths are 2.21 Å. All Nb(4)-O(6) bond lengths are 1.90 Å. There are six inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to three equivalent O(4) and three equivalent O(5) atoms to form distorted MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, 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 33-46°. All Mn(1)-O(4) bond lengths are 2.09 Å. All Mn(1)-O(5) bond lengths are 1.92 Å. In the second Mn site, Mn(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MnO6 octahedra that share corners with three equivalent Mg(1)O6 octahedra, corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(2)O6 pentagonal pyramids, and edges with three equivalent Mn(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-48°. All Mn(2)-O(1) bond lengths are 2.32 Å. All Mn(2)-O(2) bond lengths are 2.11 Å. In the third Mn site, Mn(3) is bonded to three equivalent O(4) and three equivalent O(6) atoms to form distorted MnO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra, edges with three equivalent Mn(4)O6 octahedra, and  a faceface with one Mn(1)O6 octahedra. The corner-sharing octahedral tilt angles are 54°. All Mn(3)-O(4) bond lengths are 2.29 Å. All Mn(3)-O(6) bond lengths are 2.08 Å. In the fourth Mn site, Mn(4) is bonded to three equivalent O(4) and three equivalent O(6) atoms to form MnO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra, corners with three equivalent Mn(1)O6 octahedra, and edges with three equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles are 46°. All Mn(4)-O(4) bond lengths are 2.28 Å. All Mn(4)-O(6) bond lengths are 2.16 Å. In the fifth Mn site, Mn(5) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form MnO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra, corners with three equivalent Nb(2)O6 pentagonal pyramids, edges with three equivalent Mn(2)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. All Mn(5)-O(1) bond lengths are 2.32 Å. All Mn(5)-O(2) bond lengths are 2.09 Å. In the sixth Mn site, Mn(6) is bonded in a 6-coordinate geometry to three equivalent O(1) and three equivalent O(3) atoms. All Mn(6)-O(1) bond lengths are 2.50 Å. All Mn(6)-O(3) bond lengths are 2.06 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Mg(1), 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 to one Mg(1), one Nb(2), one Nb(4), and one Mn(6) atom to form a mixture of distorted corner and edge-sharing OMgMnNb2 trigonal pyramids. In the fourth O site, O(4) is bonded to one Nb(3), one Mn(1), one Mn(3), and one Mn(4) atom to form a mixture of distorted corner and edge-sharing OMn3Nb trigonal pyramids. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Nb(1), one Nb(3), and one Mn(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Nb(4), one Mn(3), and one Mn(4) atom.