Tm2TiO5 crystallizes in the orthorhombic Cmcm space group. Tm(1) is bonded to one O(3), two equivalent O(1), and three equivalent O(2) atoms to form distorted TmO6 pentagonal pyramids that share  a cornercorner with one Ti(1)O6 octahedra, corners with three equivalent Tm(1)O6 pentagonal pyramids, edges with three equivalent Ti(1)O6 octahedra, and edges with three equivalent Tm(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 30°. Ti(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent Tm(1)O6 pentagonal pyramids, and edges with six equivalent Tm(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 33°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Tm(1) and one Ti(1) atom. In the second O site, O(2) is bonded to three equivalent Tm(1) and one Ti(1) atom to form OTm3Ti trigonal pyramids that share  a cornercorner with one O(3)Tm2Ti2 tetrahedra, corners with three equivalent O(2)Tm3Ti trigonal pyramids, edges with two equivalent O(3)Tm2Ti2 tetrahedra, and edges with two equivalent O(2)Tm3Ti trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Tm(1) and two equivalent Ti(1) atoms to form distorted OTm2Ti2 tetrahedra that share corners with two equivalent O(3)Tm2Ti2 tetrahedra, corners with two equivalent O(2)Tm3Ti trigonal pyramids, and edges with four equivalent O(2)Tm3Ti trigonal pyramids.
Tm2TiO5 crystallizes in the orthorhombic Cmcm space group. Tm(1) is bonded to one O(3), two equivalent O(1), and three equivalent O(2) atoms to form distorted TmO6 pentagonal pyramids that share  a cornercorner with one Ti(1)O6 octahedra, corners with three equivalent Tm(1)O6 pentagonal pyramids, edges with three equivalent Ti(1)O6 octahedra, and edges with three equivalent Tm(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 30°. The Tm(1)-O(3) bond length is 2.35 Å. There is one shorter (2.18 Å) and one longer (2.24 Å) Tm(1)-O(1) bond length. There are two shorter (2.16 Å) and one longer (2.32 Å) Tm(1)-O(2) bond length. Ti(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent Tm(1)O6 pentagonal pyramids, and edges with six equivalent Tm(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 33°. Both Ti(1)-O(1) bond lengths are 1.88 Å. Both Ti(1)-O(2) bond lengths are 2.11 Å. Both Ti(1)-O(3) bond lengths are 2.12 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Tm(1) and one Ti(1) atom. In the second O site, O(2) is bonded to three equivalent Tm(1) and one Ti(1) atom to form OTm3Ti trigonal pyramids that share  a cornercorner with one O(3)Tm2Ti2 tetrahedra, corners with three equivalent O(2)Tm3Ti trigonal pyramids, edges with two equivalent O(3)Tm2Ti2 tetrahedra, and edges with two equivalent O(2)Tm3Ti trigonal pyramids. In the third O site, O(3) is bonded to two equivalent Tm(1) and two equivalent Ti(1) atoms to form distorted OTm2Ti2 tetrahedra that share corners with two equivalent O(3)Tm2Ti2 tetrahedra, corners with two equivalent O(2)Tm3Ti trigonal pyramids, and edges with four equivalent O(2)Tm3Ti trigonal pyramids.