RbTl(FeSe)8 crystallizes in the tetragonal I-4m2 space group. Rb(1) is bonded in a body-centered cubic geometry to four equivalent Se(2) and four equivalent Se(3) atoms. Fe(1) is bonded in a 4-coordinate geometry to one Se(1), one Se(2), one Se(3), and one Se(4) atom. Tl(1) is bonded in a 8-coordinate geometry to four equivalent Se(1) and four equivalent Se(4) atoms. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to four equivalent Fe(1) and two equivalent Tl(1) atoms. In the second Se site, Se(2) is bonded to two equivalent Rb(1) and four equivalent Fe(1) atoms to form a mixture of distorted corner and edge-sharing SeRb2Fe4 pentagonal pyramids. In the third Se site, Se(3) is bonded to two equivalent Rb(1) and four equivalent Fe(1) atoms to form a mixture of distorted corner and edge-sharing SeRb2Fe4 pentagonal pyramids. In the fourth Se site, Se(4) is bonded in a 4-coordinate geometry to four equivalent Fe(1) and two equivalent Tl(1) atoms.
RbTl(FeSe)8 crystallizes in the tetragonal I-4m2 space group. Rb(1) is bonded in a body-centered cubic geometry to four equivalent Se(2) and four equivalent Se(3) atoms. All Rb(1)-Se(2) bond lengths are 3.49 Å. All Rb(1)-Se(3) bond lengths are 3.50 Å. Fe(1) is bonded in a 4-coordinate geometry to one Se(1), one Se(2), one Se(3), and one Se(4) atom. The Fe(1)-Se(1) bond length is 2.44 Å. The Fe(1)-Se(2) bond length is 2.44 Å. The Fe(1)-Se(3) bond length is 2.44 Å. The Fe(1)-Se(4) bond length is 2.45 Å. Tl(1) is bonded in a 8-coordinate geometry to four equivalent Se(1) and four equivalent Se(4) atoms. All Tl(1)-Se(1) bond lengths are 3.43 Å. All Tl(1)-Se(4) bond lengths are 3.43 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to four equivalent Fe(1) and two equivalent Tl(1) atoms. In the second Se site, Se(2) is bonded to two equivalent Rb(1) and four equivalent Fe(1) atoms to form a mixture of distorted corner and edge-sharing SeRb2Fe4 pentagonal pyramids. In the third Se site, Se(3) is bonded to two equivalent Rb(1) and four equivalent Fe(1) atoms to form a mixture of distorted corner and edge-sharing SeRb2Fe4 pentagonal pyramids. In the fourth Se site, Se(4) is bonded in a 4-coordinate geometry to four equivalent Fe(1) and two equivalent Tl(1) atoms.