The crystal structure described by FeO2 crystallizes in the triclinic P1 space group. There are twelve inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), one O(4), one O(6), one O(7), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one Fe(12)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, edges with two equivalent Fe(4)O6 octahedra, and edges with two equivalent Fe(6)O6 octahedra. In the second Fe site, Fe(2) is bonded to one O(10), one O(15), one O(16), one O(20), one O(5), and one O(9) atom to form edge-sharing FeO6 octahedra. In the third Fe site, Fe(3) is bonded to one O(11), one O(12), one O(5), one O(6), one O(8), and one O(9) atom to form edge-sharing FeO6 octahedra. In the fourth Fe site, Fe(4) is bonded to one O(1), one O(12), one O(3), one O(4), one O(6), and one O(7) atom to form FeO6 octahedra that share  a cornercorner with one Fe(12)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(6)O6 octahedra. In the fifth Fe site, Fe(5) is bonded to one O(10), one O(11), one O(14), one O(15), one O(16), and one O(9) atom to form edge-sharing FeO6 octahedra. In the sixth Fe site, Fe(6) is bonded to one O(1), one O(12), one O(2), one O(3), one O(7), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one Fe(12)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. In the seventh Fe site, Fe(7) is bonded to one O(13), one O(14), one O(16), one O(18), one O(19), and one O(20) atom to form edge-sharing FeO6 octahedra. In the eighth Fe site, Fe(8) is bonded to one O(10), one O(11), one O(14), one O(15), one O(20), and one O(5) atom to form edge-sharing FeO6 octahedra. In the ninth Fe site, Fe(9) is bonded to one O(17), one O(18), one O(19), one O(21), one O(22), and one O(23) atom to form FeO6 octahedra that share corners with two equivalent Fe(12)O4 tetrahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(10)O6 octahedra, and edges with two equivalent Fe(11)O6 octahedra. In the tenth Fe site, Fe(10) is bonded to one O(13), one O(17), one O(19), one O(21), one O(23), and one O(24) atom to form FeO6 octahedra that share corners with two equivalent Fe(12)O4 tetrahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(11)O6 octahedra, and edges with two equivalent Fe(9)O6 octahedra. In the eleventh Fe site, Fe(11) is bonded to one O(13), one O(17), one O(18), one O(22), one O(23), and one O(24) atom to form FeO6 octahedra that share corners with two equivalent Fe(12)O4 tetrahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(10)O6 octahedra, and edges with two equivalent Fe(9)O6 octahedra. In the twelfth Fe site, Fe(12) is bonded to one O(21), one O(22), one O(24), and one O(7) atom to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-60°. There are twenty-four inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to one Fe(4) and one Fe(6) atom. In the second O site, O(2) is bonded in a water-like geometry to one Fe(1) and one Fe(6) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(1), one Fe(4), and one Fe(6) atom. In the fourth O site, O(4) is bonded in a water-like geometry to one Fe(1) and one Fe(4) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Fe(2), one Fe(3), and one Fe(8) atom. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1), one Fe(3), and one Fe(4) atom. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Fe(1), one Fe(12), one Fe(4), and one Fe(6) atom. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1), one Fe(3), and one Fe(6) atom. In the ninth O site, O(9) is bonded in a distorted T-shaped geometry to one Fe(2), one Fe(3), and one Fe(5) atom. In the tenth O site, O(10) is bonded in a distorted trigonal non-coplanar geometry to one Fe(2), one Fe(5), and one Fe(8) atom. In the eleventh O site, O(11) is bonded in a distorted T-shaped geometry to one Fe(3), one Fe(5), and one Fe(8) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal non-coplanar geometry to one Fe(3), one Fe(4), and one Fe(6) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal non-coplanar geometry to one Fe(10), one Fe(11), and one Fe(7) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal non-coplanar geometry to one Fe(5), one Fe(7), and one Fe(8) atom. In the fifteenth O site, O(15) is bonded in a distorted T-shaped geometry to one Fe(2), one Fe(5), and one Fe(8) atom. In the sixteenth O site, O(16) is bonded in a distorted T-shaped geometry to one Fe(2), one Fe(5), and one Fe(7) atom. In the seventeenth O site, O(17) is bonded in a distorted T-shaped geometry to one Fe(10), one Fe(11), and one Fe(9) atom. In the eighteenth O site, O(18) is bonded in a distorted T-shaped geometry to one Fe(11), one Fe(7), and one Fe(9) atom. In the nineteenth O site, O(19) is bonded in a distorted T-shaped geometry to one Fe(10), one Fe(7), and one Fe(9) atom. In the twentieth O site, O(20) is bonded in a 3-coordinate geometry to one Fe(2), one Fe(7), and one Fe(8) atom. In the twenty-first O site, O(21) is bonded in a trigonal planar geometry to one Fe(10), one Fe(12), and one Fe(9) atom. In the twenty-second O site, O(22) is bonded in a distorted trigonal planar geometry to one Fe(11), one Fe(12), and one Fe(9) atom. In the twenty-third O site, O(23) is bonded in a distorted trigonal non-coplanar geometry to one Fe(10), one Fe(11), and one Fe(9) atom. In the twenty-fourth O site, O(24) is bonded in a trigonal planar geometry to one Fe(10), one Fe(11), and one Fe(12) atom. is represented by the CIF file [CIF]
data_FeO2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.940
_cell_length_b   5.973
_cell_length_c   14.501
_cell_angle_alpha   88.612
_cell_angle_beta   89.150
_cell_angle_gamma   60.387
_symmetry_Int_Tables_number   1
_cell_volume   447.149
_cell_formula_units_Z   12
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Fe  Fe0  1  0.681  0.656  0.168  1.0
  Fe  Fe1  1  0.501  0.501  0.499  1.0
  Fe  Fe2  1  0.331  0.827  0.333  1.0
  Fe  Fe3  1  0.165  0.660  0.169  1.0
  Fe  Fe4  1  1.000  0.005  0.500  1.0
  Fe  Fe5  1  0.165  0.174  0.168  1.0
  Fe  Fe6  1  0.668  0.173  0.666  1.0
  Fe  Fe7  1  0.499  0.002  0.500  1.0
  Fe  Fe8  1  0.332  0.333  0.834  1.0
  Fe  Fe9  1  0.833  0.334  0.834  1.0
  Fe  Fe10  1  0.833  0.833  0.833  1.0
  Fe  Fe11  1  0.336  0.831  0.955  1.0
  O  O12  1  0.304  0.346  0.107  1.0
  O  O13  1  0.847  0.355  0.104  1.0
  O  O14  1  0.979  0.496  0.246  1.0
  O  O15  1  0.843  0.805  0.109  1.0
  O  O16  1  0.625  0.673  0.420  1.0
  O  O17  1  0.480  0.537  0.239  1.0
  O  O18  1  0.345  0.835  0.089  1.0
  O  O19  1  0.474  0.968  0.246  1.0
  O  O20  1  0.183  0.692  0.418  1.0
  O  O21  1  0.343  0.829  0.568  1.0
  O  O22  1  0.176  0.132  0.426  1.0
  O  O23  1  0.047  0.974  0.243  1.0
  O  O24  1  0.948  0.027  0.747  1.0
  O  O25  1  0.819  0.882  0.577  1.0
  O  O26  1  0.658  0.172  0.431  1.0
  O  O27  1  0.815  0.310  0.582  1.0
  O  O28  1  0.658  0.165  0.902  1.0
  O  O29  1  0.526  0.028  0.744  1.0
  O  O30  1  0.522  0.452  0.747  1.0
  O  O31  1  0.380  0.326  0.579  1.0
  O  O32  1  0.171  0.164  0.902  1.0
  O  O33  1  0.170  0.669  0.902  1.0
  O  O34  1  0.010  0.502  0.769  1.0
  O  O35  1  0.667  0.668  0.900  1.0
[/CIF]
.
The crystal structure described by FeO2 crystallizes in the triclinic P1 space group. There are twelve inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), one O(4), one O(6), one O(7), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one Fe(12)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, edges with two equivalent Fe(4)O6 octahedra, and edges with two equivalent Fe(6)O6 octahedra. In the second Fe site, Fe(2) is bonded to one O(10), one O(15), one O(16), one O(20), one O(5), and one O(9) atom to form edge-sharing FeO6 octahedra. In the third Fe site, Fe(3) is bonded to one O(11), one O(12), one O(5), one O(6), one O(8), and one O(9) atom to form edge-sharing FeO6 octahedra. In the fourth Fe site, Fe(4) is bonded to one O(1), one O(12), one O(3), one O(4), one O(6), and one O(7) atom to form FeO6 octahedra that share  a cornercorner with one Fe(12)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(6)O6 octahedra. In the fifth Fe site, Fe(5) is bonded to one O(10), one O(11), one O(14), one O(15), one O(16), and one O(9) atom to form edge-sharing FeO6 octahedra. In the sixth Fe site, Fe(6) is bonded to one O(1), one O(12), one O(2), one O(3), one O(7), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one Fe(12)O4 tetrahedra,  an edgeedge with one Fe(3)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. In the seventh Fe site, Fe(7) is bonded to one O(13), one O(14), one O(16), one O(18), one O(19), and one O(20) atom to form edge-sharing FeO6 octahedra. In the eighth Fe site, Fe(8) is bonded to one O(10), one O(11), one O(14), one O(15), one O(20), and one O(5) atom to form edge-sharing FeO6 octahedra. In the ninth Fe site, Fe(9) is bonded to one O(17), one O(18), one O(19), one O(21), one O(22), and one O(23) atom to form FeO6 octahedra that share corners with two equivalent Fe(12)O4 tetrahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(10)O6 octahedra, and edges with two equivalent Fe(11)O6 octahedra. In the tenth Fe site, Fe(10) is bonded to one O(13), one O(17), one O(19), one O(21), one O(23), and one O(24) atom to form FeO6 octahedra that share corners with two equivalent Fe(12)O4 tetrahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(11)O6 octahedra, and edges with two equivalent Fe(9)O6 octahedra. In the eleventh Fe site, Fe(11) is bonded to one O(13), one O(17), one O(18), one O(22), one O(23), and one O(24) atom to form FeO6 octahedra that share corners with two equivalent Fe(12)O4 tetrahedra,  an edgeedge with one Fe(7)O6 octahedra, edges with two equivalent Fe(10)O6 octahedra, and edges with two equivalent Fe(9)O6 octahedra. In the twelfth Fe site, Fe(12) is bonded to one O(21), one O(22), one O(24), and one O(7) atom to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-60°. There are twenty-four inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to one Fe(4) and one Fe(6) atom. In the second O site, O(2) is bonded in a water-like geometry to one Fe(1) and one Fe(6) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(1), one Fe(4), and one Fe(6) atom. In the fourth O site, O(4) is bonded in a water-like geometry to one Fe(1) and one Fe(4) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Fe(2), one Fe(3), and one Fe(8) atom. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1), one Fe(3), and one Fe(4) atom. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to one Fe(1), one Fe(12), one Fe(4), and one Fe(6) atom. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1), one Fe(3), and one Fe(6) atom. In the ninth O site, O(9) is bonded in a distorted T-shaped geometry to one Fe(2), one Fe(3), and one Fe(5) atom. In the tenth O site, O(10) is bonded in a distorted trigonal non-coplanar geometry to one Fe(2), one Fe(5), and one Fe(8) atom. In the eleventh O site, O(11) is bonded in a distorted T-shaped geometry to one Fe(3), one Fe(5), and one Fe(8) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal non-coplanar geometry to one Fe(3), one Fe(4), and one Fe(6) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal non-coplanar geometry to one Fe(10), one Fe(11), and one Fe(7) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal non-coplanar geometry to one Fe(5), one Fe(7), and one Fe(8) atom. In the fifteenth O site, O(15) is bonded in a distorted T-shaped geometry to one Fe(2), one Fe(5), and one Fe(8) atom. In the sixteenth O site, O(16) is bonded in a distorted T-shaped geometry to one Fe(2), one Fe(5), and one Fe(7) atom. In the seventeenth O site, O(17) is bonded in a distorted T-shaped geometry to one Fe(10), one Fe(11), and one Fe(9) atom. In the eighteenth O site, O(18) is bonded in a distorted T-shaped geometry to one Fe(11), one Fe(7), and one Fe(9) atom. In the nineteenth O site, O(19) is bonded in a distorted T-shaped geometry to one Fe(10), one Fe(7), and one Fe(9) atom. In the twentieth O site, O(20) is bonded in a 3-coordinate geometry to one Fe(2), one Fe(7), and one Fe(8) atom. In the twenty-first O site, O(21) is bonded in a trigonal planar geometry to one Fe(10), one Fe(12), and one Fe(9) atom. In the twenty-second O site, O(22) is bonded in a distorted trigonal planar geometry to one Fe(11), one Fe(12), and one Fe(9) atom. In the twenty-third O site, O(23) is bonded in a distorted trigonal non-coplanar geometry to one Fe(10), one Fe(11), and one Fe(9) atom. In the twenty-fourth O site, O(24) is bonded in a trigonal planar geometry to one Fe(10), one Fe(11), and one Fe(12) atom. is represented by the CIF file [CIF]
data_FeO2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.940
_cell_length_b   5.973
_cell_length_c   14.501
_cell_angle_alpha   88.612
_cell_angle_beta   89.150
_cell_angle_gamma   60.387
_symmetry_Int_Tables_number   1
_cell_volume   447.149
_cell_formula_units_Z   12
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Fe  Fe0  1  0.681  0.656  0.168  1.0
  Fe  Fe1  1  0.501  0.501  0.499  1.0
  Fe  Fe2  1  0.331  0.827  0.333  1.0
  Fe  Fe3  1  0.165  0.660  0.169  1.0
  Fe  Fe4  1  1.000  0.005  0.500  1.0
  Fe  Fe5  1  0.165  0.174  0.168  1.0
  Fe  Fe6  1  0.668  0.173  0.666  1.0
  Fe  Fe7  1  0.499  0.002  0.500  1.0
  Fe  Fe8  1  0.332  0.333  0.834  1.0
  Fe  Fe9  1  0.833  0.334  0.834  1.0
  Fe  Fe10  1  0.833  0.833  0.833  1.0
  Fe  Fe11  1  0.336  0.831  0.955  1.0
  O  O12  1  0.304  0.346  0.107  1.0
  O  O13  1  0.847  0.355  0.104  1.0
  O  O14  1  0.979  0.496  0.246  1.0
  O  O15  1  0.843  0.805  0.109  1.0
  O  O16  1  0.625  0.673  0.420  1.0
  O  O17  1  0.480  0.537  0.239  1.0
  O  O18  1  0.345  0.835  0.089  1.0
  O  O19  1  0.474  0.968  0.246  1.0
  O  O20  1  0.183  0.692  0.418  1.0
  O  O21  1  0.343  0.829  0.568  1.0
  O  O22  1  0.176  0.132  0.426  1.0
  O  O23  1  0.047  0.974  0.243  1.0
  O  O24  1  0.948  0.027  0.747  1.0
  O  O25  1  0.819  0.882  0.577  1.0
  O  O26  1  0.658  0.172  0.431  1.0
  O  O27  1  0.815  0.310  0.582  1.0
  O  O28  1  0.658  0.165  0.902  1.0
  O  O29  1  0.526  0.028  0.744  1.0
  O  O30  1  0.522  0.452  0.747  1.0
  O  O31  1  0.380  0.326  0.579  1.0
  O  O32  1  0.171  0.164  0.902  1.0
  O  O33  1  0.170  0.669  0.902  1.0
  O  O34  1  0.010  0.502  0.769  1.0
  O  O35  1  0.667  0.668  0.900  1.0
[/CIF]
.