TiTa6Tl2O18 crystallizes in the monoclinic C2 space group. Ti(1) is bonded to two equivalent O(7), two equivalent O(8), and two equivalent O(9) atoms to form TiO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, and corners with two equivalent Ta(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 34-35°. There are three inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(2), one O(3), one O(6), one O(7), and two equivalent O(5) atoms to form distorted TaO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, corners with two equivalent Ta(3)O6 octahedra,  an edgeedge with one Ta(1)O6 octahedra, and  an edgeedge with one Ta(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-49°. In the second Ta site, Ta(2) is bonded to one O(1), one O(3), one O(6), one O(8), and two equivalent O(4) atoms to form distorted TaO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(3)O6 octahedra,  an edgeedge with one Ta(2)O6 octahedra, and  an edgeedge with one Ta(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 25-50°. In the third Ta site, Ta(3) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(9) atom to form distorted TaO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra,  an edgeedge with one Ta(1)O6 octahedra, and  an edgeedge with one Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 25-50°. Tl(1) is bonded in a distorted single-bond geometry to one O(2) atom. There are nine inequivalent O sites. In the first O site, O(9) is bonded in a bent 150 degrees geometry to one Ti(1) and one Ta(3) atom. In the second O site, O(1) is bonded in a bent 150 degrees geometry to one Ta(2) and one Ta(3) atom. In the third O site, O(2) is bonded in a bent 150 degrees geometry to one Ta(1), one Ta(3), and one Tl(1) atom. In the fourth O site, O(3) is bonded in a bent 150 degrees geometry to one Ta(1) and one Ta(2) atom. In the fifth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Ta(3) and two equivalent Ta(2) atoms. In the sixth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Ta(3) and two equivalent Ta(1) atoms. In the seventh O site, O(6) is bonded in a trigonal non-coplanar geometry to one Ta(1), one Ta(2), and one Ta(3) atom. In the eighth O site, O(7) is bonded in a bent 150 degrees geometry to one Ti(1) and one Ta(1) atom. In the ninth O site, O(8) is bonded in a bent 150 degrees geometry to one Ti(1) and one Ta(2) atom.
TiTa6Tl2O18 crystallizes in the monoclinic C2 space group. Ti(1) is bonded to two equivalent O(7), two equivalent O(8), and two equivalent O(9) atoms to form TiO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, and corners with two equivalent Ta(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 34-35°. Both Ti(1)-O(7) bond lengths are 1.97 Å. Both Ti(1)-O(8) bond lengths are 1.97 Å. Both Ti(1)-O(9) bond lengths are 1.98 Å. There are three inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(2), one O(3), one O(6), one O(7), and two equivalent O(5) atoms to form distorted TaO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra, corners with two equivalent Ta(3)O6 octahedra,  an edgeedge with one Ta(1)O6 octahedra, and  an edgeedge with one Ta(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-49°. The Ta(1)-O(2) bond length is 1.96 Å. The Ta(1)-O(3) bond length is 1.93 Å. The Ta(1)-O(6) bond length is 2.13 Å. The Ta(1)-O(7) bond length is 1.86 Å. There is one shorter (2.09 Å) and one longer (2.13 Å) Ta(1)-O(5) bond length. In the second Ta site, Ta(2) is bonded to one O(1), one O(3), one O(6), one O(8), and two equivalent O(4) atoms to form distorted TaO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(3)O6 octahedra,  an edgeedge with one Ta(2)O6 octahedra, and  an edgeedge with one Ta(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 25-50°. The Ta(2)-O(1) bond length is 1.94 Å. The Ta(2)-O(3) bond length is 1.95 Å. The Ta(2)-O(6) bond length is 2.11 Å. The Ta(2)-O(8) bond length is 1.86 Å. There is one shorter (2.11 Å) and one longer (2.14 Å) Ta(2)-O(4) bond length. In the third Ta site, Ta(3) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(9) atom to form distorted TaO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, corners with two equivalent Ta(2)O6 octahedra,  an edgeedge with one Ta(1)O6 octahedra, and  an edgeedge with one Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 25-50°. The Ta(3)-O(1) bond length is 1.93 Å. The Ta(3)-O(2) bond length is 1.96 Å. The Ta(3)-O(4) bond length is 2.12 Å. The Ta(3)-O(5) bond length is 2.09 Å. The Ta(3)-O(6) bond length is 2.13 Å. The Ta(3)-O(9) bond length is 1.86 Å. Tl(1) is bonded in a distorted single-bond geometry to one O(2) atom. The Tl(1)-O(2) bond length is 2.79 Å. There are nine inequivalent O sites. In the first O site, O(9) is bonded in a bent 150 degrees geometry to one Ti(1) and one Ta(3) atom. In the second O site, O(1) is bonded in a bent 150 degrees geometry to one Ta(2) and one Ta(3) atom. In the third O site, O(2) is bonded in a bent 150 degrees geometry to one Ta(1), one Ta(3), and one Tl(1) atom. In the fourth O site, O(3) is bonded in a bent 150 degrees geometry to one Ta(1) and one Ta(2) atom. In the fifth O site, O(4) is bonded in a trigonal non-coplanar geometry to one Ta(3) and two equivalent Ta(2) atoms. In the sixth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Ta(3) and two equivalent Ta(1) atoms. In the seventh O site, O(6) is bonded in a trigonal non-coplanar geometry to one Ta(1), one Ta(2), and one Ta(3) atom. In the eighth O site, O(7) is bonded in a bent 150 degrees geometry to one Ti(1) and one Ta(1) atom. In the ninth O site, O(8) is bonded in a bent 150 degrees geometry to one Ti(1) and one Ta(2) atom.