Cs4FeO4 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to one O(1), one O(3), one O(4), and two equivalent O(2) atoms to form distorted CsO5 square pyramids that share corners with three equivalent Fe(1)O4 tetrahedra,  an edgeedge with one Cs(1)O5 square pyramid, and  an edgeedge with one Fe(1)O4 tetrahedra. In the second Cs site, Cs(2) is bonded in a 5-coordinate geometry to two equivalent O(3) and three equivalent O(2) atoms. In the third Cs site, Cs(3) is bonded in a 4-coordinate geometry to one O(3), one O(4), and two equivalent O(1) atoms. In the fourth Cs site, Cs(4) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(1), and two equivalent O(4) atoms. 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 three equivalent Cs(1)O5 square pyramids and  an edgeedge with one Cs(1)O5 square pyramid. There are four inequivalent O sites. In the first O site, O(4) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(3), two equivalent Cs(4), and one Fe(1) atom. In the second O site, O(1) is bonded in a 1-coordinate geometry to one Cs(1), two equivalent Cs(3), two equivalent Cs(4), and one Fe(1) atom. In the third O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Cs(1), three equivalent Cs(2), and one Fe(1) atom. In the fourth O site, O(3) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(3), one Cs(4), two equivalent Cs(2), and one Fe(1) atom.
Cs4FeO4 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Cs sites. In the first Cs site, Cs(1) is bonded to one O(1), one O(3), one O(4), and two equivalent O(2) atoms to form distorted CsO5 square pyramids that share corners with three equivalent Fe(1)O4 tetrahedra,  an edgeedge with one Cs(1)O5 square pyramid, and  an edgeedge with one Fe(1)O4 tetrahedra. The Cs(1)-O(1) bond length is 3.07 Å. The Cs(1)-O(3) bond length is 2.98 Å. The Cs(1)-O(4) bond length is 3.09 Å. There is one shorter (2.98 Å) and one longer (3.00 Å) Cs(1)-O(2) bond length. In the second Cs site, Cs(2) is bonded in a 5-coordinate geometry to two equivalent O(3) and three equivalent O(2) atoms. There is one shorter (2.95 Å) and one longer (3.38 Å) Cs(2)-O(3) bond length. There are a spread of Cs(2)-O(2) bond distances ranging from 3.04-3.21 Å. In the third Cs site, Cs(3) is bonded in a 4-coordinate geometry to one O(3), one O(4), and two equivalent O(1) atoms. The Cs(3)-O(3) bond length is 2.88 Å. The Cs(3)-O(4) bond length is 2.96 Å. There is one shorter (2.90 Å) and one longer (3.10 Å) Cs(3)-O(1) bond length. In the fourth Cs site, Cs(4) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(1), and two equivalent O(4) atoms. The Cs(4)-O(3) bond length is 3.17 Å. There is one shorter (2.98 Å) and one longer (3.16 Å) Cs(4)-O(1) bond length. There is one shorter (2.89 Å) and one longer (3.22 Å) Cs(4)-O(4) bond length. 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 three equivalent Cs(1)O5 square pyramids and  an edgeedge with one Cs(1)O5 square pyramid. The Fe(1)-O(1) bond length is 1.81 Å. The Fe(1)-O(2) bond length is 1.78 Å. The Fe(1)-O(3) bond length is 1.81 Å. The Fe(1)-O(4) bond length is 1.82 Å. There are four inequivalent O sites. In the first O site, O(4) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(3), two equivalent Cs(4), and one Fe(1) atom. In the second O site, O(1) is bonded in a 1-coordinate geometry to one Cs(1), two equivalent Cs(3), two equivalent Cs(4), and one Fe(1) atom. In the third O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Cs(1), three equivalent Cs(2), and one Fe(1) atom. In the fourth O site, O(3) is bonded in a distorted single-bond geometry to one Cs(1), one Cs(3), one Cs(4), two equivalent Cs(2), and one Fe(1) atom.