Cs3TmO3 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form distorted CsO4 tetrahedra that share corners with five equivalent Tm(1)O4 tetrahedra and  an edgeedge with one Cs(1)O4 tetrahedra. In the second Cs site, Cs(2) is bonded in a 4-coordinate geometry to one O(2), one O(3), and two equivalent O(1) atoms. In the third Cs site, Cs(3) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(3) atoms. Tm(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form TmO4 tetrahedra that share corners with five equivalent Cs(1)O4 tetrahedra and  an edgeedge with one Tm(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 7-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), two equivalent Cs(3), and one Tm(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cs(3), and two equivalent Tm(1) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Cs(1), one Cs(2), two equivalent Cs(3), and one Tm(1) atom.
Cs3TmO3 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form distorted CsO4 tetrahedra that share corners with five equivalent Tm(1)O4 tetrahedra and  an edgeedge with one Cs(1)O4 tetrahedra. The Cs(1)-O(2) bond length is 2.94 Å. The Cs(1)-O(3) bond length is 2.91 Å. There is one shorter (2.99 Å) and one longer (3.28 Å) Cs(1)-O(1) bond length. In the second Cs site, Cs(2) is bonded in a 4-coordinate geometry to one O(2), one O(3), and two equivalent O(1) atoms. The Cs(2)-O(2) bond length is 3.14 Å. The Cs(2)-O(3) bond length is 3.12 Å. There is one shorter (2.97 Å) and one longer (3.33 Å) Cs(2)-O(1) bond length. In the third Cs site, Cs(3) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(3) atoms. The Cs(3)-O(2) bond length is 3.20 Å. There is one shorter (3.25 Å) and one longer (3.39 Å) Cs(3)-O(1) bond length. There is one shorter (2.85 Å) and one longer (3.18 Å) Cs(3)-O(3) bond length. Tm(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form TmO4 tetrahedra that share corners with five equivalent Cs(1)O4 tetrahedra and  an edgeedge with one Tm(1)O4 tetrahedra. The Tm(1)-O(1) bond length is 2.08 Å. The Tm(1)-O(3) bond length is 2.07 Å. There is one shorter (2.15 Å) and one longer (2.16 Å) Tm(1)-O(2) bond length. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 7-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), two equivalent Cs(3), and one Tm(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Cs(1), one Cs(2), one Cs(3), and two equivalent Tm(1) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Cs(1), one Cs(2), two equivalent Cs(3), and one Tm(1) atom.