MgTi5NbO12 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(6) atoms to form MgO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, edges with two equivalent Ti(2)O6 octahedra, and edges with two equivalent Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(5), and two equivalent O(6) atoms. In the second Ti site, Ti(2) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form TiO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra,  an edgeedge with one Ti(2)O6 octahedra, and  an edgeedge with one Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-53°. In the third Ti site, Ti(3) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Ti(2)O6 octahedra. The corner-sharing octahedral tilt angles are 43°. Nb(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NbO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Ti(3)O6 octahedra, and corners with six equivalent Ti(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-53°. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Ti(1), one Ti(2), and one Nb(1) atom to form distorted OMgTi2Nb trigonal pyramids that share corners with two equivalent O(1)MgTi2Nb trigonal pyramids, corners with two equivalent O(6)MgTi3 trigonal pyramids, and  an edgeedge with one O(6)MgTi3 trigonal pyramid. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ti(1), one Ti(2), and one Nb(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Ti(2), and one Ti(3) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Ti(2), one Ti(3), and one Nb(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Ti(1) and two equivalent Ti(2) atoms. In the sixth O site, O(6) is bonded to one Mg(1), one Ti(3), and two equivalent Ti(1) atoms to form distorted OMgTi3 trigonal pyramids that share corners with two equivalent O(1)MgTi2Nb trigonal pyramids, corners with two equivalent O(6)MgTi3 trigonal pyramids,  an edgeedge with one O(1)MgTi2Nb trigonal pyramid, and  an edgeedge with one O(6)MgTi3 trigonal pyramid.
MgTi5NbO12 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(6) atoms to form MgO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, edges with two equivalent Ti(2)O6 octahedra, and edges with two equivalent Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles are 52°. Both Mg(1)-O(1) bond lengths are 2.12 Å. Both Mg(1)-O(3) bond lengths are 1.95 Å. Both Mg(1)-O(6) bond lengths are 2.10 Å. There are three inequivalent Ti sites. In the first Ti site, Ti(1) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(5), and two equivalent O(6) atoms. The Ti(1)-O(1) bond length is 2.02 Å. The Ti(1)-O(2) bond length is 1.95 Å. The Ti(1)-O(5) bond length is 1.81 Å. There is one shorter (1.98 Å) and one longer (2.04 Å) Ti(1)-O(6) bond length. In the second Ti site, Ti(2) is bonded to one O(1), one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form TiO6 octahedra that share corners with three equivalent Nb(1)O6 octahedra,  an edgeedge with one Mg(1)O6 octahedra,  an edgeedge with one Ti(2)O6 octahedra, and  an edgeedge with one Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 47-53°. The Ti(2)-O(1) bond length is 2.18 Å. The Ti(2)-O(2) bond length is 1.96 Å. The Ti(2)-O(3) bond length is 1.91 Å. The Ti(2)-O(4) bond length is 1.94 Å. There is one shorter (2.04 Å) and one longer (2.11 Å) Ti(2)-O(5) bond length. In the third Ti site, Ti(3) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Ti(2)O6 octahedra. The corner-sharing octahedral tilt angles are 43°. Both Ti(3)-O(3) bond lengths are 1.96 Å. Both Ti(3)-O(4) bond lengths are 2.06 Å. Both Ti(3)-O(6) bond lengths are 2.12 Å. Nb(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NbO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Ti(3)O6 octahedra, and corners with six equivalent Ti(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-53°. Both Nb(1)-O(1) bond lengths are 2.11 Å. Both Nb(1)-O(2) bond lengths are 2.08 Å. Both Nb(1)-O(4) bond lengths are 2.09 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Ti(1), one Ti(2), and one Nb(1) atom to form distorted OMgTi2Nb trigonal pyramids that share corners with two equivalent O(1)MgTi2Nb trigonal pyramids, corners with two equivalent O(6)MgTi3 trigonal pyramids, and  an edgeedge with one O(6)MgTi3 trigonal pyramid. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ti(1), one Ti(2), and one Nb(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Ti(2), and one Ti(3) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Ti(2), one Ti(3), and one Nb(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Ti(1) and two equivalent Ti(2) atoms. In the sixth O site, O(6) is bonded to one Mg(1), one Ti(3), and two equivalent Ti(1) atoms to form distorted OMgTi3 trigonal pyramids that share corners with two equivalent O(1)MgTi2Nb trigonal pyramids, corners with two equivalent O(6)MgTi3 trigonal pyramids,  an edgeedge with one O(1)MgTi2Nb trigonal pyramid, and  an edgeedge with one O(6)MgTi3 trigonal pyramid.