FeO2 is trigonal omega-like structured and crystallizes in the orthorhombic Imma space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form edge-sharing FeO6 octahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form edge-sharing FeO6 octahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Fe(1) and two equivalent Fe(2) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Fe(2) and two equivalent Fe(1) atoms.
FeO2 is trigonal omega-like structured and crystallizes in the orthorhombic Imma space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form edge-sharing FeO6 octahedra. Both Fe(1)-O(1) bond lengths are 1.89 Å. All Fe(1)-O(2) bond lengths are 1.98 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form edge-sharing FeO6 octahedra. Both Fe(2)-O(2) bond lengths are 1.99 Å. All Fe(2)-O(1) bond lengths are 2.02 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Fe(1) and two equivalent Fe(2) atoms. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Fe(2) and two equivalent Fe(1) atoms.