Bi2Fe4O9 crystallizes in the orthorhombic Pbam space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with four equivalent Fe(2)O4 tetrahedra and edges with two equivalent Fe(1)O6 octahedra. In the second Fe site, Fe(2) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form FeO4 tetrahedra that share corners with four equivalent Fe(1)O6 octahedra and  a cornercorner with one Fe(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-62°. Bi(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(2) and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Fe(2) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Fe(1), one Fe(2), and one Bi(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Fe(2) and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Fe(1) and two equivalent Bi(1) atoms to form a mixture of distorted corner and edge-sharing OFe2Bi2 tetrahedra.
Bi2Fe4O9 crystallizes in the orthorhombic Pbam space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with four equivalent Fe(2)O4 tetrahedra and edges with two equivalent Fe(1)O6 octahedra. Both Fe(1)-O(2) bond lengths are 2.04 Å. Both Fe(1)-O(3) bond lengths are 1.99 Å. Both Fe(1)-O(4) bond lengths are 2.05 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form FeO4 tetrahedra that share corners with four equivalent Fe(1)O6 octahedra and  a cornercorner with one Fe(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-62°. The Fe(2)-O(1) bond length is 1.84 Å. The Fe(2)-O(3) bond length is 1.88 Å. Both Fe(2)-O(2) bond lengths are 1.91 Å. Bi(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Bi(1)-O(2) bond lengths are 2.14 Å. There is one shorter (2.19 Å) and one longer (2.47 Å) Bi(1)-O(4) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Fe(2) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Fe(1), one Fe(2), and one Bi(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Fe(2) and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded to two equivalent Fe(1) and two equivalent Bi(1) atoms to form a mixture of distorted corner and edge-sharing OFe2Bi2 tetrahedra.