Tm2O3 crystallizes in the monoclinic C2/m space group. There are three inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 7-coordinate geometry to two equivalent O(1), two equivalent O(3), and three equivalent O(2) atoms. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(2), one O(5), two equivalent O(1), and three equivalent O(4) atoms. In the third Tm site, Tm(3) is bonded to one O(1), one O(4), two equivalent O(3), and two equivalent O(5) atoms to form a mixture of distorted corner and edge-sharing TmO6 octahedra. The corner-sharing octahedra are not tilted. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Tm(3), two equivalent Tm(1), and two equivalent Tm(2) atoms to form distorted OTm5 square pyramids that share corners with two equivalent O(3)Tm4 tetrahedra, corners with five equivalent O(4)Tm4 tetrahedra, corners with two equivalent O(2)Tm4 trigonal pyramids, edges with two equivalent O(5)Tm6 octahedra, edges with two equivalent O(1)Tm5 square pyramids,  an edgeedge with one O(4)Tm4 tetrahedra, edges with two equivalent O(3)Tm4 tetrahedra, and edges with three equivalent O(2)Tm4 trigonal pyramids. In the second O site, O(2) is bonded to one Tm(2) and three equivalent Tm(1) atoms to form distorted OTm4 trigonal pyramids that share  a cornercorner with one O(5)Tm6 octahedra, corners with two equivalent O(1)Tm5 square pyramids, corners with three equivalent O(4)Tm4 tetrahedra, corners with six equivalent O(3)Tm4 tetrahedra, corners with two equivalent O(2)Tm4 trigonal pyramids, edges with three equivalent O(1)Tm5 square pyramids, and edges with two equivalent O(2)Tm4 trigonal pyramids. The corner-sharing octahedral tilt angles are 37°. In the third O site, O(3) is bonded to two equivalent Tm(1) and two equivalent Tm(3) atoms to form OTm4 tetrahedra that share corners with two equivalent O(5)Tm6 octahedra, corners with two equivalent O(1)Tm5 square pyramids, corners with two equivalent O(3)Tm4 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra, corners with six equivalent O(2)Tm4 trigonal pyramids,  an edgeedge with one O(5)Tm6 octahedra, edges with two equivalent O(1)Tm5 square pyramids, and  an edgeedge with one O(3)Tm4 tetrahedra. The corner-sharing octahedral tilt angles are 13°. In the fourth O site, O(4) is bonded to one Tm(3) and three equivalent Tm(2) atoms to form OTm4 tetrahedra that share  a cornercorner with one O(5)Tm6 octahedra, corners with five equivalent O(1)Tm5 square pyramids, corners with two equivalent O(3)Tm4 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra, corners with three equivalent O(2)Tm4 trigonal pyramids, edges with two equivalent O(5)Tm6 octahedra,  an edgeedge with one O(1)Tm5 square pyramid, and edges with two equivalent O(4)Tm4 tetrahedra. The corner-sharing octahedral tilt angles are 49°. In the fifth O site, O(5) is bonded to two equivalent Tm(2) and four equivalent Tm(3) atoms to form OTm6 octahedra that share corners with two equivalent O(4)Tm4 tetrahedra, corners with four equivalent O(3)Tm4 tetrahedra, corners with two equivalent O(2)Tm4 trigonal pyramids, edges with two equivalent O(5)Tm6 octahedra, edges with four equivalent O(1)Tm5 square pyramids, edges with two equivalent O(3)Tm4 tetrahedra, and edges with four equivalent O(4)Tm4 tetrahedra.
Tm2O3 crystallizes in the monoclinic C2/m space group. There are three inequivalent Tm sites. In the first Tm site, Tm(1) is bonded in a 7-coordinate geometry to two equivalent O(1), two equivalent O(3), and three equivalent O(2) atoms. Both Tm(1)-O(1) bond lengths are 2.42 Å. There is one shorter (2.21 Å) and one longer (2.37 Å) Tm(1)-O(3) bond length. There are two shorter (2.19 Å) and one longer (2.50 Å) Tm(1)-O(2) bond length. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(2), one O(5), two equivalent O(1), and three equivalent O(4) atoms. The Tm(2)-O(2) bond length is 2.25 Å. The Tm(2)-O(5) bond length is 2.67 Å. Both Tm(2)-O(1) bond lengths are 2.35 Å. There is one shorter (2.19 Å) and two longer (2.20 Å) Tm(2)-O(4) bond lengths. In the third Tm site, Tm(3) is bonded to one O(1), one O(4), two equivalent O(3), and two equivalent O(5) atoms to form a mixture of distorted corner and edge-sharing TmO6 octahedra. The corner-sharing octahedra are not tilted. The Tm(3)-O(1) bond length is 2.20 Å. The Tm(3)-O(4) bond length is 2.14 Å. Both Tm(3)-O(3) bond lengths are 2.15 Å. Both Tm(3)-O(5) bond lengths are 2.41 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to one Tm(3), two equivalent Tm(1), and two equivalent Tm(2) atoms to form distorted OTm5 square pyramids that share corners with two equivalent O(3)Tm4 tetrahedra, corners with five equivalent O(4)Tm4 tetrahedra, corners with two equivalent O(2)Tm4 trigonal pyramids, edges with two equivalent O(5)Tm6 octahedra, edges with two equivalent O(1)Tm5 square pyramids,  an edgeedge with one O(4)Tm4 tetrahedra, edges with two equivalent O(3)Tm4 tetrahedra, and edges with three equivalent O(2)Tm4 trigonal pyramids. In the second O site, O(2) is bonded to one Tm(2) and three equivalent Tm(1) atoms to form distorted OTm4 trigonal pyramids that share  a cornercorner with one O(5)Tm6 octahedra, corners with two equivalent O(1)Tm5 square pyramids, corners with three equivalent O(4)Tm4 tetrahedra, corners with six equivalent O(3)Tm4 tetrahedra, corners with two equivalent O(2)Tm4 trigonal pyramids, edges with three equivalent O(1)Tm5 square pyramids, and edges with two equivalent O(2)Tm4 trigonal pyramids. The corner-sharing octahedral tilt angles are 37°. In the third O site, O(3) is bonded to two equivalent Tm(1) and two equivalent Tm(3) atoms to form OTm4 tetrahedra that share corners with two equivalent O(5)Tm6 octahedra, corners with two equivalent O(1)Tm5 square pyramids, corners with two equivalent O(3)Tm4 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra, corners with six equivalent O(2)Tm4 trigonal pyramids,  an edgeedge with one O(5)Tm6 octahedra, edges with two equivalent O(1)Tm5 square pyramids, and  an edgeedge with one O(3)Tm4 tetrahedra. The corner-sharing octahedral tilt angles are 13°. In the fourth O site, O(4) is bonded to one Tm(3) and three equivalent Tm(2) atoms to form OTm4 tetrahedra that share  a cornercorner with one O(5)Tm6 octahedra, corners with five equivalent O(1)Tm5 square pyramids, corners with two equivalent O(3)Tm4 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra, corners with three equivalent O(2)Tm4 trigonal pyramids, edges with two equivalent O(5)Tm6 octahedra,  an edgeedge with one O(1)Tm5 square pyramid, and edges with two equivalent O(4)Tm4 tetrahedra. The corner-sharing octahedral tilt angles are 49°. In the fifth O site, O(5) is bonded to two equivalent Tm(2) and four equivalent Tm(3) atoms to form OTm6 octahedra that share corners with two equivalent O(4)Tm4 tetrahedra, corners with four equivalent O(3)Tm4 tetrahedra, corners with two equivalent O(2)Tm4 trigonal pyramids, edges with two equivalent O(5)Tm6 octahedra, edges with four equivalent O(1)Tm5 square pyramids, edges with two equivalent O(3)Tm4 tetrahedra, and edges with four equivalent O(4)Tm4 tetrahedra.