BaSr4(FeO2)5 crystallizes in the tetragonal P4/mmm space group. Ba(1) is bonded in a distorted body-centered cubic geometry to eight equivalent O(1) atoms. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(2) atoms. In the second Sr site, Sr(2) is bonded in a body-centered cubic geometry to four equivalent O(2) and four equivalent O(3) atoms. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a rectangular see-saw-like geometry to four equivalent O(1) atoms. In the second Fe site, Fe(2) is bonded in a rectangular see-saw-like geometry to four equivalent O(2) atoms. In the third Fe site, Fe(3) is bonded in a square co-planar geometry to four equivalent O(3) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), two equivalent Sr(1), and two equivalent Fe(1) atoms to form OBa2Sr2Fe2 octahedra that share corners with six equivalent O(2)Sr4Fe2 octahedra, corners with eight equivalent O(1)Ba2Sr2Fe2 octahedra,  an edgeedge with one O(2)Sr4Fe2 octahedra, edges with three equivalent O(1)Ba2Sr2Fe2 octahedra, and faces with four equivalent O(1)Ba2Sr2Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-65°. In the second O site, O(2) is bonded to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Fe(2) atoms to form OSr4Fe2 octahedra that share corners with two equivalent O(2)Sr4Fe2 octahedra, corners with six equivalent O(1)Ba2Sr2Fe2 octahedra, corners with six equivalent O(3)Sr4Fe2 octahedra,  an edgeedge with one O(1)Ba2Sr2Fe2 octahedra,  an edgeedge with one O(3)Sr4Fe2 octahedra, edges with two equivalent O(2)Sr4Fe2 octahedra, and faces with four equivalent O(2)Sr4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-65°. In the third O site, O(3) is bonded to four equivalent Sr(2) and two equivalent Fe(3) atoms to form a mixture of face, corner, and edge-sharing OSr4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-65°.
BaSr4(FeO2)5 crystallizes in the tetragonal P4/mmm space group. Ba(1) is bonded in a distorted body-centered cubic geometry to eight equivalent O(1) atoms. All Ba(1)-O(1) bond lengths are 2.82 Å. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(2) atoms. All Sr(1)-O(1) bond lengths are 2.65 Å. All Sr(1)-O(2) bond lengths are 2.69 Å. In the second Sr site, Sr(2) is bonded in a body-centered cubic geometry to four equivalent O(2) and four equivalent O(3) atoms. All Sr(2)-O(2) bond lengths are 2.68 Å. All Sr(2)-O(3) bond lengths are 2.69 Å. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a rectangular see-saw-like geometry to four equivalent O(1) atoms. All Fe(1)-O(1) bond lengths are 2.04 Å. In the second Fe site, Fe(2) is bonded in a rectangular see-saw-like geometry to four equivalent O(2) atoms. All Fe(2)-O(2) bond lengths are 2.04 Å. In the third Fe site, Fe(3) is bonded in a square co-planar geometry to four equivalent O(3) atoms. All Fe(3)-O(3) bond lengths are 2.04 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), two equivalent Sr(1), and two equivalent Fe(1) atoms to form OBa2Sr2Fe2 octahedra that share corners with six equivalent O(2)Sr4Fe2 octahedra, corners with eight equivalent O(1)Ba2Sr2Fe2 octahedra,  an edgeedge with one O(2)Sr4Fe2 octahedra, edges with three equivalent O(1)Ba2Sr2Fe2 octahedra, and faces with four equivalent O(1)Ba2Sr2Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-65°. In the second O site, O(2) is bonded to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Fe(2) atoms to form OSr4Fe2 octahedra that share corners with two equivalent O(2)Sr4Fe2 octahedra, corners with six equivalent O(1)Ba2Sr2Fe2 octahedra, corners with six equivalent O(3)Sr4Fe2 octahedra,  an edgeedge with one O(1)Ba2Sr2Fe2 octahedra,  an edgeedge with one O(3)Sr4Fe2 octahedra, edges with two equivalent O(2)Sr4Fe2 octahedra, and faces with four equivalent O(2)Sr4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-65°. In the third O site, O(3) is bonded to four equivalent Sr(2) and two equivalent Fe(3) atoms to form a mixture of face, corner, and edge-sharing OSr4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-65°.