Cs4Rb2Fe2O5 crystallizes in the monoclinic C2/m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(2) atoms. In the second Cs site, Cs(2) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(2) atoms. Rb(1) is bonded to four equivalent O(2) atoms to form distorted edge-sharing RbO4 tetrahedra. Fe(1) is bonded in a trigonal planar geometry to one O(1) and two equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Fe(1) atoms. In the second O site, O(2) is bonded in a 7-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), two equivalent Rb(1), and one Fe(1) atom.
Cs4Rb2Fe2O5 crystallizes in the monoclinic C2/m space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(2) atoms. The Cs(1)-O(1) bond length is 3.51 Å. There are two shorter (3.16 Å) and two longer (3.37 Å) Cs(1)-O(2) bond lengths. In the second Cs site, Cs(2) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(2) atoms. The Cs(2)-O(1) bond length is 3.02 Å. There are two shorter (3.07 Å) and two longer (3.20 Å) Cs(2)-O(2) bond lengths. Rb(1) is bonded to four equivalent O(2) atoms to form distorted edge-sharing RbO4 tetrahedra. There are two shorter (2.81 Å) and two longer (2.94 Å) Rb(1)-O(2) bond lengths. Fe(1) is bonded in a trigonal planar geometry to one O(1) and two equivalent O(2) atoms. The Fe(1)-O(1) bond length is 1.94 Å. Both Fe(1)-O(2) bond lengths are 1.91 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Fe(1) atoms. In the second O site, O(2) is bonded in a 7-coordinate geometry to two equivalent Cs(1), two equivalent Cs(2), two equivalent Rb(1), and one Fe(1) atom.