Rb4K2Fe2O5 crystallizes in the monoclinic C2/m space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(2) atoms. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(2) atoms. K(1) is bonded to four equivalent O(2) atoms to form distorted edge-sharing KO4 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 octahedral geometry to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Fe(1) atoms. In the second O site, O(2) is bonded in a 7-coordinate geometry to two equivalent Rb(1), two equivalent Rb(2), two equivalent K(1), and one Fe(1) atom.
Rb4K2Fe2O5 crystallizes in the monoclinic C2/m space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(2) atoms. The Rb(1)-O(1) bond length is 2.91 Å. There are two shorter (2.86 Å) and two longer (3.15 Å) Rb(1)-O(2) bond lengths. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(1) and four equivalent O(2) atoms. The Rb(2)-O(1) bond length is 3.23 Å. There are two shorter (3.06 Å) and two longer (3.23 Å) Rb(2)-O(2) bond lengths. K(1) is bonded to four equivalent O(2) atoms to form distorted edge-sharing KO4 tetrahedra. There are two shorter (2.66 Å) and two longer (2.75 Å) K(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 1.90 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted octahedral geometry to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Fe(1) atoms. In the second O site, O(2) is bonded in a 7-coordinate geometry to two equivalent Rb(1), two equivalent Rb(2), two equivalent K(1), and one Fe(1) atom.