FeO2 is trigonal omega-like structured and crystallizes in the tetragonal I4_1/amd space group. Fe(1) is bonded to six equivalent O(1) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 23°. O(1) is bonded in a T-shaped geometry to three equivalent Fe(1) atoms.
FeO2 is trigonal omega-like structured and crystallizes in the tetragonal I4_1/amd space group. Fe(1) is bonded to six equivalent O(1) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 23°. There are two shorter (1.92 Å) and four longer (1.97 Å) Fe(1)-O(1) bond lengths. O(1) is bonded in a T-shaped geometry to three equivalent Fe(1) atoms.