Cs5FeO4 crystallizes in the monoclinic P2_1/c space group. There are five inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. In the second Cs site, Cs(2) is bonded in a 4-coordinate geometry to one O(2), one O(4), and two equivalent O(1) atoms. In the third Cs site, Cs(3) is bonded to one O(1), one O(4), and two equivalent O(3) atoms to form distorted CsO4 tetrahedra that share corners with two equivalent Fe(1)O4 tetrahedra,  an edgeedge with one Cs(3)O4 tetrahedra, and  an edgeedge with one Fe(1)O4 tetrahedra. In the fourth Cs site, Cs(4) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(4), and two equivalent O(2) atoms. In the fifth Cs site, Cs(5) is bonded in a 3-coordinate geometry to one O(1), one O(3), and one O(4) atom. Fe(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form FeO4 tetrahedra that share corners with two equivalent Cs(3)O4 tetrahedra and  an edgeedge with one Cs(3)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(3) is bonded in a 1-coordinate geometry to one Cs(5), two equivalent Cs(1), two equivalent Cs(3), and one Fe(1) atom. In the second O site, O(4) is bonded in a distorted single-bond geometry to one Cs(2), one Cs(3), one Cs(4), one Cs(5), two equivalent Cs(1), and one Fe(1) atom. In the third O site, O(1) is bonded to one Cs(3), one Cs(4), one Cs(5), two equivalent Cs(2), and one Fe(1) atom to form distorted corner-sharing OCs5Fe octahedra. The corner-sharing octahedral tilt angles are 61°. In the fourth O site, O(2) is bonded in a 6-coordinate geometry to one Cs(2), two equivalent Cs(1), two equivalent Cs(4), and one Fe(1) atom.
Cs5FeO4 crystallizes in the monoclinic P2_1/c space group. There are five inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. There is one shorter (2.96 Å) and one longer (3.10 Å) Cs(1)-O(2) bond length. There is one shorter (2.99 Å) and one longer (3.54 Å) Cs(1)-O(3) bond length. There is one shorter (3.44 Å) and one longer (3.56 Å) Cs(1)-O(4) bond length. In the second Cs site, Cs(2) is bonded in a 4-coordinate geometry to one O(2), one O(4), and two equivalent O(1) atoms. The Cs(2)-O(2) bond length is 3.13 Å. The Cs(2)-O(4) bond length is 3.00 Å. There is one shorter (2.73 Å) and one longer (3.17 Å) Cs(2)-O(1) bond length. In the third Cs site, Cs(3) is bonded to one O(1), one O(4), and two equivalent O(3) atoms to form distorted CsO4 tetrahedra that share corners with two equivalent Fe(1)O4 tetrahedra,  an edgeedge with one Cs(3)O4 tetrahedra, and  an edgeedge with one Fe(1)O4 tetrahedra. The Cs(3)-O(1) bond length is 2.87 Å. The Cs(3)-O(4) bond length is 2.96 Å. There is one shorter (2.93 Å) and one longer (3.05 Å) Cs(3)-O(3) bond length. In the fourth Cs site, Cs(4) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(4), and two equivalent O(2) atoms. The Cs(4)-O(1) bond length is 2.96 Å. The Cs(4)-O(4) bond length is 3.03 Å. There is one shorter (2.84 Å) and one longer (2.91 Å) Cs(4)-O(2) bond length. In the fifth Cs site, Cs(5) is bonded in a 3-coordinate geometry to one O(1), one O(3), and one O(4) atom. The Cs(5)-O(1) bond length is 3.14 Å. The Cs(5)-O(3) bond length is 2.97 Å. The Cs(5)-O(4) bond length is 2.94 Å. Fe(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form FeO4 tetrahedra that share corners with two equivalent Cs(3)O4 tetrahedra and  an edgeedge with one Cs(3)O4 tetrahedra. The Fe(1)-O(1) bond length is 1.92 Å. The Fe(1)-O(2) bond length is 1.92 Å. The Fe(1)-O(3) bond length is 1.90 Å. The Fe(1)-O(4) bond length is 1.91 Å. There are four inequivalent O sites. In the first O site, O(3) is bonded in a 1-coordinate geometry to one Cs(5), two equivalent Cs(1), two equivalent Cs(3), and one Fe(1) atom. In the second O site, O(4) is bonded in a distorted single-bond geometry to one Cs(2), one Cs(3), one Cs(4), one Cs(5), two equivalent Cs(1), and one Fe(1) atom. In the third O site, O(1) is bonded to one Cs(3), one Cs(4), one Cs(5), two equivalent Cs(2), and one Fe(1) atom to form distorted corner-sharing OCs5Fe octahedra. The corner-sharing octahedral tilt angles are 61°. In the fourth O site, O(2) is bonded in a 6-coordinate geometry to one Cs(2), two equivalent Cs(1), two equivalent Cs(4), and one Fe(1) atom.