FeO2 is Hydrophilite-like structured and crystallizes in the monoclinic P2/m space group. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(4), two equivalent O(5), and two equivalent O(6) atoms to form a mixture of edge and corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 50°. In the second Fe site, Fe(2) is bonded to one O(2), one O(3), two equivalent O(7), and two equivalent O(8) atoms to form a mixture of edge and corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. In the third Fe site, Fe(3) is bonded to one O(5), one O(8), two equivalent O(1), and two equivalent O(2) atoms to form a mixture of edge and corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. In the fourth Fe site, Fe(4) is bonded to one O(6), one O(7), two equivalent O(3), and two equivalent O(4) atoms to form a mixture of edge and corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 50°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1) and two equivalent Fe(3) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Fe(2) and two equivalent Fe(3) atoms. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Fe(2) and two equivalent Fe(4) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Fe(1) and two equivalent Fe(4) atoms. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(3) and two equivalent Fe(1) atoms. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Fe(4) and two equivalent Fe(1) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Fe(4) and two equivalent Fe(2) atoms. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Fe(3) and two equivalent Fe(2) atoms.
FeO2 is Hydrophilite-like structured and crystallizes in the monoclinic P2/m space group. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(4), two equivalent O(5), and two equivalent O(6) atoms to form a mixture of edge and corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 50°. The Fe(1)-O(1) bond length is 2.10 Å. The Fe(1)-O(4) bond length is 2.01 Å. Both Fe(1)-O(5) bond lengths are 1.92 Å. Both Fe(1)-O(6) bond lengths are 1.93 Å. In the second Fe site, Fe(2) is bonded to one O(2), one O(3), two equivalent O(7), and two equivalent O(8) atoms to form a mixture of edge and corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. The Fe(2)-O(2) bond length is 1.99 Å. The Fe(2)-O(3) bond length is 2.06 Å. Both Fe(2)-O(7) bond lengths are 1.93 Å. Both Fe(2)-O(8) bond lengths are 1.94 Å. In the third Fe site, Fe(3) is bonded to one O(5), one O(8), two equivalent O(1), and two equivalent O(2) atoms to form a mixture of edge and corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. The Fe(3)-O(5) bond length is 2.08 Å. The Fe(3)-O(8) bond length is 1.99 Å. Both Fe(3)-O(1) bond lengths are 1.93 Å. Both Fe(3)-O(2) bond lengths are 1.94 Å. In the fourth Fe site, Fe(4) is bonded to one O(6), one O(7), two equivalent O(3), and two equivalent O(4) atoms to form a mixture of edge and corner-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles are 50°. The Fe(4)-O(6) bond length is 2.02 Å. The Fe(4)-O(7) bond length is 2.10 Å. Both Fe(4)-O(3) bond lengths are 1.93 Å. Both Fe(4)-O(4) bond lengths are 1.93 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1) and two equivalent Fe(3) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Fe(2) and two equivalent Fe(3) atoms. In the third O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Fe(2) and two equivalent Fe(4) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Fe(1) and two equivalent Fe(4) atoms. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(3) and two equivalent Fe(1) atoms. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Fe(4) and two equivalent Fe(1) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Fe(4) and two equivalent Fe(2) atoms. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Fe(3) and two equivalent Fe(2) atoms.