MgTi5NbO12 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(12), one O(2), one O(3), one O(7), and one O(9) atom to form MgO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra,  an edgeedge with one Ti(2)O6 octahedra,  an edgeedge with one Ti(3)O6 octahedra, and edges with two equivalent Ti(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-51°. There are five inequivalent Ti sites. In the first Ti site, Ti(1) is bonded in a 5-coordinate geometry to one O(1), one O(10), one O(12), one O(5), and one O(9) atom. In the second Ti site, Ti(2) is bonded to one O(1), one O(10), one O(3), one O(5), one O(6), and one O(8) atom 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(3)O6 octahedra, and  an edgeedge with one Ti(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-53°. In the third Ti site, Ti(3) is bonded to one O(11), one O(2), one O(4), one O(5), one O(7), and one O(8) atom 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(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 45-53°. In the fourth Ti site, Ti(4) is bonded in a 5-coordinate geometry to one O(11), one O(12), one O(2), one O(8), and one O(9) atom. In the fifth Ti site, Ti(5) is bonded to one O(12), one O(3), one O(4), one O(6), one O(7), and one O(9) atom to form TiO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra,  an edgeedge with one Ti(2)O6 octahedra,  an edgeedge with one Ti(3)O6 octahedra, and edges with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-46°. Nb(1) is bonded to one O(1), one O(10), one O(11), one O(2), one O(4), and one O(6) atom to form NbO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Ti(5)O6 octahedra, corners with three equivalent Ti(2)O6 octahedra, and corners with three equivalent Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-53°. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ti(1), one Ti(2), and one Nb(1) atom. In the second O site, O(2) is bonded to one Mg(1), one Ti(3), one Ti(4), and one Nb(1) atom to form distorted OMgTi2Nb trigonal pyramids that share corners with two equivalent O(10)MgTi2Nb trigonal pyramids, corners with two equivalent O(9)MgTi3 trigonal pyramids, and  an edgeedge with one O(12)MgTi3 trigonal pyramid. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Ti(2), and one Ti(5) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Ti(3), one Ti(5), and one Nb(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Ti(1), one Ti(2), and one Ti(3) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Ti(2), one Ti(5), and one Nb(1) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Ti(3), and one Ti(5) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Ti(2), one Ti(3), and one Ti(4) atom. In the ninth O site, O(9) is bonded to one Mg(1), one Ti(1), one Ti(4), and one Ti(5) atom to form distorted OMgTi3 trigonal pyramids that share corners with two equivalent O(2)MgTi2Nb trigonal pyramids, corners with two equivalent O(12)MgTi3 trigonal pyramids,  an edgeedge with one O(10)MgTi2Nb trigonal pyramid, and  an edgeedge with one O(12)MgTi3 trigonal pyramid. In the tenth O site, O(10) 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(2)MgTi2Nb trigonal pyramids, corners with two equivalent O(12)MgTi3 trigonal pyramids, and  an edgeedge with one O(9)MgTi3 trigonal pyramid. In the eleventh O site, O(11) is bonded in a distorted T-shaped geometry to one Ti(3), one Ti(4), and one Nb(1) atom. In the twelfth O site, O(12) is bonded to one Mg(1), one Ti(1), one Ti(4), and one Ti(5) atom to form distorted OMgTi3 trigonal pyramids that share corners with two equivalent O(10)MgTi2Nb trigonal pyramids, corners with two equivalent O(9)MgTi3 trigonal pyramids,  an edgeedge with one O(2)MgTi2Nb trigonal pyramid, and  an edgeedge with one O(9)MgTi3 trigonal pyramid.
MgTi5NbO12 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(10), one O(12), one O(2), one O(3), one O(7), and one O(9) atom to form MgO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra,  an edgeedge with one Ti(2)O6 octahedra,  an edgeedge with one Ti(3)O6 octahedra, and edges with two equivalent Ti(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-51°. The Mg(1)-O(10) bond length is 2.09 Å. The Mg(1)-O(12) bond length is 2.08 Å. The Mg(1)-O(2) bond length is 2.11 Å. The Mg(1)-O(3) bond length is 1.94 Å. The Mg(1)-O(7) bond length is 1.94 Å. The Mg(1)-O(9) bond length is 2.10 Å. There are five inequivalent Ti sites. In the first Ti site, Ti(1) is bonded in a 5-coordinate geometry to one O(1), one O(10), one O(12), one O(5), and one O(9) atom. The Ti(1)-O(1) bond length is 1.95 Å. The Ti(1)-O(10) bond length is 2.05 Å. The Ti(1)-O(12) bond length is 1.97 Å. The Ti(1)-O(5) bond length is 1.83 Å. The Ti(1)-O(9) bond length is 2.07 Å. In the second Ti site, Ti(2) is bonded to one O(1), one O(10), one O(3), one O(5), one O(6), and one O(8) atom 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(3)O6 octahedra, and  an edgeedge with one Ti(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 46-53°. The Ti(2)-O(1) bond length is 1.94 Å. The Ti(2)-O(10) bond length is 2.17 Å. The Ti(2)-O(3) bond length is 1.95 Å. The Ti(2)-O(5) bond length is 2.07 Å. The Ti(2)-O(6) bond length is 1.96 Å. The Ti(2)-O(8) bond length is 2.00 Å. In the third Ti site, Ti(3) is bonded to one O(11), one O(2), one O(4), one O(5), one O(7), and one O(8) atom 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(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 45-53°. The Ti(3)-O(11) bond length is 1.95 Å. The Ti(3)-O(2) bond length is 2.14 Å. The Ti(3)-O(4) bond length is 1.96 Å. The Ti(3)-O(5) bond length is 2.01 Å. The Ti(3)-O(7) bond length is 1.95 Å. The Ti(3)-O(8) bond length is 2.07 Å. In the fourth Ti site, Ti(4) is bonded in a 5-coordinate geometry to one O(11), one O(12), one O(2), one O(8), and one O(9) atom. The Ti(4)-O(11) bond length is 1.96 Å. The Ti(4)-O(12) bond length is 2.08 Å. The Ti(4)-O(2) bond length is 2.03 Å. The Ti(4)-O(8) bond length is 1.83 Å. The Ti(4)-O(9) bond length is 2.01 Å. In the fifth Ti site, Ti(5) is bonded to one O(12), one O(3), one O(4), one O(6), one O(7), and one O(9) atom to form TiO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra,  an edgeedge with one Ti(2)O6 octahedra,  an edgeedge with one Ti(3)O6 octahedra, and edges with two equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-46°. The Ti(5)-O(12) bond length is 2.16 Å. The Ti(5)-O(3) bond length is 1.95 Å. The Ti(5)-O(4) bond length is 2.03 Å. The Ti(5)-O(6) bond length is 2.03 Å. The Ti(5)-O(7) bond length is 1.95 Å. The Ti(5)-O(9) bond length is 2.06 Å. Nb(1) is bonded to one O(1), one O(10), one O(11), one O(2), one O(4), and one O(6) atom to form NbO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Ti(5)O6 octahedra, corners with three equivalent Ti(2)O6 octahedra, and corners with three equivalent Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 43-53°. The Nb(1)-O(1) bond length is 2.08 Å. The Nb(1)-O(10) bond length is 2.10 Å. The Nb(1)-O(11) bond length is 2.05 Å. The Nb(1)-O(2) bond length is 2.09 Å. The Nb(1)-O(4) bond length is 2.09 Å. The Nb(1)-O(6) bond length is 2.09 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ti(1), one Ti(2), and one Nb(1) atom. In the second O site, O(2) is bonded to one Mg(1), one Ti(3), one Ti(4), and one Nb(1) atom to form distorted OMgTi2Nb trigonal pyramids that share corners with two equivalent O(10)MgTi2Nb trigonal pyramids, corners with two equivalent O(9)MgTi3 trigonal pyramids, and  an edgeedge with one O(12)MgTi3 trigonal pyramid. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Ti(2), and one Ti(5) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Ti(3), one Ti(5), and one Nb(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to one Ti(1), one Ti(2), and one Ti(3) atom. In the sixth O site, O(6) is bonded in a distorted T-shaped geometry to one Ti(2), one Ti(5), and one Nb(1) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Ti(3), and one Ti(5) atom. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Ti(2), one Ti(3), and one Ti(4) atom. In the ninth O site, O(9) is bonded to one Mg(1), one Ti(1), one Ti(4), and one Ti(5) atom to form distorted OMgTi3 trigonal pyramids that share corners with two equivalent O(2)MgTi2Nb trigonal pyramids, corners with two equivalent O(12)MgTi3 trigonal pyramids,  an edgeedge with one O(10)MgTi2Nb trigonal pyramid, and  an edgeedge with one O(12)MgTi3 trigonal pyramid. In the tenth O site, O(10) 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(2)MgTi2Nb trigonal pyramids, corners with two equivalent O(12)MgTi3 trigonal pyramids, and  an edgeedge with one O(9)MgTi3 trigonal pyramid. In the eleventh O site, O(11) is bonded in a distorted T-shaped geometry to one Ti(3), one Ti(4), and one Nb(1) atom. In the twelfth O site, O(12) is bonded to one Mg(1), one Ti(1), one Ti(4), and one Ti(5) atom to form distorted OMgTi3 trigonal pyramids that share corners with two equivalent O(10)MgTi2Nb trigonal pyramids, corners with two equivalent O(9)MgTi3 trigonal pyramids,  an edgeedge with one O(2)MgTi2Nb trigonal pyramid, and  an edgeedge with one O(9)MgTi3 trigonal pyramid.