Tm2TiO5 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(3), two equivalent O(1), and three equivalent O(4) atoms to form distorted TmO6 octahedra that share corners with two equivalent Tm(2)O6 octahedra, corners with four equivalent Ti(1)O6 octahedra, edges with two equivalent Tm(2)O6 octahedra, and edges with four equivalent Tm(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-66°. In the second Tm site, Tm(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form TmO6 octahedra that share corners with two equivalent Tm(1)O6 octahedra, corners with two equivalent Tm(2)O6 octahedra, corners with four equivalent Ti(1)O6 octahedra, edges with two equivalent Tm(1)O6 octahedra, and edges with two equivalent Tm(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-64°. Ti(1) is bonded to one O(3), one O(4), one O(5), and three equivalent O(2) atoms to form distorted TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with four equivalent Tm(1)O6 octahedra, corners with four equivalent Tm(2)O6 octahedra, and edges with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 34-66°. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form OTm4 tetrahedra that share corners with two equivalent O(3)Tm3Ti tetrahedra, corners with four equivalent O(4)Tm3Ti tetrahedra, corners with four equivalent O(1)Tm4 tetrahedra,  an edgeedge with one O(4)Tm3Ti tetrahedra, and edges with two equivalent O(3)Tm3Ti tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to three equivalent Ti(1) atoms. In the third O site, O(3) is bonded to one Tm(1), two equivalent Tm(2), and one Ti(1) atom to form OTm3Ti tetrahedra that share corners with two equivalent O(3)Tm3Ti tetrahedra, corners with two equivalent O(1)Tm4 tetrahedra, corners with four equivalent O(4)Tm3Ti tetrahedra, and edges with two equivalent O(1)Tm4 tetrahedra. In the fourth O site, O(4) is bonded to three equivalent Tm(1) and one Ti(1) atom to form OTm3Ti tetrahedra that share corners with two equivalent O(4)Tm3Ti tetrahedra, corners with four equivalent O(3)Tm3Ti tetrahedra, corners with four equivalent O(1)Tm4 tetrahedra,  an edgeedge with one O(1)Tm4 tetrahedra, and edges with two equivalent O(4)Tm3Ti tetrahedra. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Tm(2) and one Ti(1) atom.
Tm2TiO5 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(3), two equivalent O(1), and three equivalent O(4) atoms to form distorted TmO6 octahedra that share corners with two equivalent Tm(2)O6 octahedra, corners with four equivalent Ti(1)O6 octahedra, edges with two equivalent Tm(2)O6 octahedra, and edges with four equivalent Tm(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-66°. The Tm(1)-O(3) bond length is 2.29 Å. Both Tm(1)-O(1) bond lengths are 2.28 Å. There is one shorter (2.26 Å) and two longer (2.29 Å) Tm(1)-O(4) bond lengths. In the second Tm site, Tm(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form TmO6 octahedra that share corners with two equivalent Tm(1)O6 octahedra, corners with two equivalent Tm(2)O6 octahedra, corners with four equivalent Ti(1)O6 octahedra, edges with two equivalent Tm(1)O6 octahedra, and edges with two equivalent Tm(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-64°. There is one shorter (2.18 Å) and one longer (2.21 Å) Tm(2)-O(1) bond length. Both Tm(2)-O(3) bond lengths are 2.27 Å. Both Tm(2)-O(5) bond lengths are 2.31 Å. Ti(1) is bonded to one O(3), one O(4), one O(5), and three equivalent O(2) atoms to form distorted TiO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with four equivalent Tm(1)O6 octahedra, corners with four equivalent Tm(2)O6 octahedra, and edges with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 34-66°. The Ti(1)-O(3) bond length is 2.07 Å. The Ti(1)-O(4) bond length is 2.03 Å. The Ti(1)-O(5) bond length is 1.85 Å. There are two shorter (1.88 Å) and one longer (2.36 Å) Ti(1)-O(2) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form OTm4 tetrahedra that share corners with two equivalent O(3)Tm3Ti tetrahedra, corners with four equivalent O(4)Tm3Ti tetrahedra, corners with four equivalent O(1)Tm4 tetrahedra,  an edgeedge with one O(4)Tm3Ti tetrahedra, and edges with two equivalent O(3)Tm3Ti tetrahedra. In the second O site, O(2) is bonded in a 3-coordinate geometry to three equivalent Ti(1) atoms. In the third O site, O(3) is bonded to one Tm(1), two equivalent Tm(2), and one Ti(1) atom to form OTm3Ti tetrahedra that share corners with two equivalent O(3)Tm3Ti tetrahedra, corners with two equivalent O(1)Tm4 tetrahedra, corners with four equivalent O(4)Tm3Ti tetrahedra, and edges with two equivalent O(1)Tm4 tetrahedra. In the fourth O site, O(4) is bonded to three equivalent Tm(1) and one Ti(1) atom to form OTm3Ti tetrahedra that share corners with two equivalent O(4)Tm3Ti tetrahedra, corners with four equivalent O(3)Tm3Ti tetrahedra, corners with four equivalent O(1)Tm4 tetrahedra,  an edgeedge with one O(1)Tm4 tetrahedra, and edges with two equivalent O(4)Tm3Ti tetrahedra. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Tm(2) and one Ti(1) atom.