Rb3TlO3 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(2), and two equivalent O(3) atoms. In the second Rb site, Rb(2) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form distorted RbO4 trigonal pyramids that share corners with five equivalent Tl(1)O4 tetrahedra and  an edgeedge with one Rb(2)O4 trigonal pyramid. In the third Rb site, Rb(3) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(3) atoms. Tl(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form TlO4 tetrahedra that share corners with five equivalent Rb(2)O4 trigonal pyramids and  an edgeedge with one Tl(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Rb(1), one Rb(2), two equivalent Rb(3), and one Tl(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(3), two equivalent Rb(1), and two equivalent Tl(1) atoms. In the third O site, O(3) is bonded in a 7-coordinate geometry to two equivalent Rb(1), two equivalent Rb(2), two equivalent Rb(3), and one Tl(1) atom.
Rb3TlO3 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 5-coordinate geometry to one O(1), two equivalent O(2), and two equivalent O(3) atoms. The Rb(1)-O(1) bond length is 2.94 Å. There is one shorter (2.84 Å) and one longer (3.23 Å) Rb(1)-O(2) bond length. There is one shorter (2.86 Å) and one longer (3.23 Å) Rb(1)-O(3) bond length. In the second Rb site, Rb(2) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form distorted RbO4 trigonal pyramids that share corners with five equivalent Tl(1)O4 tetrahedra and  an edgeedge with one Rb(2)O4 trigonal pyramid. The Rb(2)-O(1) bond length is 2.76 Å. The Rb(2)-O(2) bond length is 2.81 Å. There is one shorter (2.74 Å) and one longer (3.01 Å) Rb(2)-O(3) bond length. In the third Rb site, Rb(3) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(1), and two equivalent O(3) atoms. The Rb(3)-O(2) bond length is 2.87 Å. There is one shorter (2.71 Å) and one longer (2.95 Å) Rb(3)-O(1) bond length. There is one shorter (3.04 Å) and one longer (3.24 Å) Rb(3)-O(3) bond length. Tl(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form TlO4 tetrahedra that share corners with five equivalent Rb(2)O4 trigonal pyramids and  an edgeedge with one Tl(1)O4 tetrahedra. The Tl(1)-O(1) bond length is 2.12 Å. The Tl(1)-O(3) bond length is 2.12 Å. Both Tl(1)-O(2) bond lengths are 2.25 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Rb(1), one Rb(2), two equivalent Rb(3), and one Tl(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Rb(2), one Rb(3), two equivalent Rb(1), and two equivalent Tl(1) atoms. In the third O site, O(3) is bonded in a 7-coordinate geometry to two equivalent Rb(1), two equivalent Rb(2), two equivalent Rb(3), and one Tl(1) atom.