The material described by FeO2 crystallizes in the monoclinic Cm space group. There are twelve inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one Fe(12)O4 tetrahedra, corners with two equivalent Fe(5)O4 tetrahedra,  an edgeedge with one Fe(11)O6 octahedra,  an edgeedge with one Fe(2)O6 octahedra, and edges with two equivalent Fe(1)O6 octahedra. In the second Fe site, Fe(2) is bonded to one O(4), one O(9), two equivalent O(5), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with three equivalent Fe(5)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. In the third Fe site, Fe(3) is bonded to one O(15), one O(7), and two equivalent O(10) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-56°. In the fourth Fe site, Fe(4) is bonded to one O(11), one O(12), one O(14), one O(5), one O(7), and one O(9) atom to form FeO6 octahedra that share  a cornercorner with one Fe(3)O4 tetrahedra,  a cornercorner with one Fe(5)O4 tetrahedra, corners with two equivalent Fe(8)O4 tetrahedra,  an edgeedge with one Fe(2)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. In the fifth Fe site, Fe(5) is bonded to one O(14), one O(4), and two equivalent O(6) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-60°. In the sixth Fe site, Fe(6) is bonded to one O(13), one O(21), and two equivalent O(17) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-56°. In the seventh Fe site, Fe(7) is bonded to one O(10), one O(13), one O(15), one O(16), one O(18), and one O(20) atom to form FeO6 octahedra that share  a cornercorner with one Fe(6)O4 tetrahedra,  a cornercorner with one Fe(8)O4 tetrahedra, corners with two equivalent Fe(10)O4 tetrahedra, corners with two equivalent Fe(3)O4 tetrahedra, and edges with two equivalent Fe(7)O6 octahedra. In the eighth Fe site, Fe(8) is bonded to one O(11), one O(20), and two equivalent O(12) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-55°. In the ninth Fe site, Fe(9) is bonded to one O(17), one O(19), one O(21), one O(22), one O(23), and one O(24) atom to form FeO6 octahedra that share  a cornercorner with one Fe(10)O4 tetrahedra, corners with two equivalent Fe(12)O4 tetrahedra, corners with two equivalent Fe(6)O4 tetrahedra,  an edgeedge with one Fe(11)O6 octahedra, and edges with two equivalent Fe(9)O6 octahedra. In the tenth Fe site, Fe(10) is bonded to one O(16), one O(24), and two equivalent O(18) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-57°. In the eleventh Fe site, Fe(11) is bonded to one O(22), one O(3), two equivalent O(1), and two equivalent O(23) atoms to form FeO6 octahedra that share corners with three equivalent Fe(12)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(9)O6 octahedra. In the twelfth Fe site, Fe(12) is bonded to one O(22), one O(8), and two equivalent O(23) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-58°. There are twenty-four inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to one Fe(1) and one Fe(11) atom. In the second O site, O(2) is bonded in a water-like geometry to two equivalent Fe(1) atoms. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(11) and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Fe(2), one Fe(5), and two equivalent Fe(1) atoms. In the fifth O site, O(5) is bonded in a water-like geometry to one Fe(2) and one Fe(4) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Fe(1), one Fe(2), and one Fe(5) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(3) and two equivalent Fe(4) atoms. In the eighth O site, O(8) is bonded in a trigonal planar geometry to one Fe(12) and two equivalent Fe(1) atoms. In the ninth O site, O(9) is bonded in a distorted T-shaped geometry to one Fe(2) and two equivalent Fe(4) atoms. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Fe(3) and one Fe(7) atom. In the eleventh O site, O(11) is bonded in a trigonal planar geometry to one Fe(8) and two equivalent Fe(4) atoms. In the twelfth O site, O(12) is bonded in a bent 120 degrees geometry to one Fe(4) and one Fe(8) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal planar geometry to one Fe(6) and two equivalent Fe(7) atoms. In the fourteenth O site, O(14) is bonded in a distorted trigonal planar geometry to one Fe(5) and two equivalent Fe(4) atoms. In the fifteenth O site, O(15) is bonded in a trigonal planar geometry to one Fe(3) and two equivalent Fe(7) atoms. In the sixteenth O site, O(16) is bonded in a distorted trigonal planar geometry to one Fe(10) and two equivalent Fe(7) atoms. In the seventeenth O site, O(17) is bonded in a bent 120 degrees geometry to one Fe(6) and one Fe(9) atom. In the eighteenth O site, O(18) is bonded in a bent 120 degrees geometry to one Fe(10) and one Fe(7) atom. In the nineteenth O site, O(19) is bonded in a water-like geometry to two equivalent Fe(9) atoms. In the twentieth O site, O(20) is bonded in a distorted trigonal planar geometry to one Fe(8) and two equivalent Fe(7) atoms. In the twenty-first O site, O(21) is bonded in a distorted trigonal planar geometry to one Fe(6) and two equivalent Fe(9) atoms. In the twenty-second O site, O(22) is bonded in a distorted rectangular see-saw-like geometry to one Fe(11), one Fe(12), and two equivalent Fe(9) atoms. In the twenty-third O site, O(23) is bonded in a trigonal planar geometry to one Fe(11), one Fe(12), and one Fe(9) atom. In the twenty-fourth O site, O(24) is bonded in a trigonal planar geometry to one Fe(10) and two equivalent Fe(9) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_FeO2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.862
_cell_length_b   5.862
_cell_length_c   19.465
_cell_angle_alpha   81.085
_cell_angle_beta   81.085
_cell_angle_gamma   61.217
_symmetry_Int_Tables_number   1
_cell_volume   576.647
_cell_formula_units_Z   16
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  0.634  0.118  0.125  1.0
  Fe  Fe1  1  0.247  0.247  0.254  1.0
  Fe  Fe2  1  0.118  0.634  0.125  1.0
  Fe  Fe3  1  0.150  0.150  0.535  1.0
  Fe  Fe4  1  0.871  0.372  0.378  1.0
  Fe  Fe5  1  0.604  0.604  0.221  1.0
  Fe  Fe6  1  0.401  0.401  0.779  1.0
  Fe  Fe7  1  0.372  0.871  0.378  1.0
  Fe  Fe8  1  0.123  0.625  0.624  1.0
  Fe  Fe9  1  0.851  0.851  0.466  1.0
  Fe  Fe10  1  0.625  0.123  0.624  1.0
  Fe  Fe11  1  0.874  0.383  0.870  1.0
  Fe  Fe12  1  0.383  0.874  0.870  1.0
  Fe  Fe13  1  0.098  0.098  0.716  1.0
  Fe  Fe14  1  0.997  0.997  0.002  1.0
  Fe  Fe15  1  0.353  0.353  0.971  1.0
  O  O16  1  0.261  0.816  0.063  1.0
  O  O17  1  0.925  0.925  0.176  1.0
  O  O18  1  0.816  0.261  0.063  1.0
  O  O19  1  0.816  0.816  0.066  1.0
  O  O20  1  0.431  0.431  0.188  1.0
  O  O21  1  0.508  0.063  0.314  1.0
  O  O22  1  0.440  0.969  0.190  1.0
  O  O23  1  0.174  0.174  0.438  1.0
  O  O24  1  0.063  0.508  0.314  1.0
  O  O25  1  0.326  0.326  0.071  1.0
  O  O26  1  0.075  0.075  0.318  1.0
  O  O27  1  0.969  0.440  0.190  1.0
  O  O28  1  0.806  0.292  0.568  1.0
  O  O29  1  0.692  0.692  0.428  1.0
  O  O30  1  0.704  0.196  0.432  1.0
  O  O31  1  0.430  0.430  0.682  1.0
  O  O32  1  0.292  0.806  0.568  1.0
  O  O33  1  0.569  0.569  0.319  1.0
  O  O34  1  0.314  0.314  0.569  1.0
  O  O35  1  0.196  0.704  0.432  1.0
  O  O36  1  0.934  0.934  0.681  1.0
  O  O37  1  0.072  0.542  0.816  1.0
  O  O38  1  0.958  0.441  0.683  1.0
  O  O39  1  0.687  0.687  0.916  1.0
  O  O40  1  0.542  0.072  0.816  1.0
  O  O41  1  0.822  0.822  0.565  1.0
  O  O42  1  0.557  0.557  0.817  1.0
  O  O43  1  0.441  0.958  0.683  1.0
  O  O44  1  0.182  0.182  0.937  1.0
  O  O45  1  0.196  0.718  0.940  1.0
  O  O46  1  0.078  0.078  0.816  1.0
  O  O47  1  0.718  0.196  0.940  1.0
[/CIF]
.
The material described by FeO2 crystallizes in the monoclinic Cm space group. There are twelve inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one Fe(12)O4 tetrahedra, corners with two equivalent Fe(5)O4 tetrahedra,  an edgeedge with one Fe(11)O6 octahedra,  an edgeedge with one Fe(2)O6 octahedra, and edges with two equivalent Fe(1)O6 octahedra. In the second Fe site, Fe(2) is bonded to one O(4), one O(9), two equivalent O(5), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with three equivalent Fe(5)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. In the third Fe site, Fe(3) is bonded to one O(15), one O(7), and two equivalent O(10) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-56°. In the fourth Fe site, Fe(4) is bonded to one O(11), one O(12), one O(14), one O(5), one O(7), and one O(9) atom to form FeO6 octahedra that share  a cornercorner with one Fe(3)O4 tetrahedra,  a cornercorner with one Fe(5)O4 tetrahedra, corners with two equivalent Fe(8)O4 tetrahedra,  an edgeedge with one Fe(2)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. In the fifth Fe site, Fe(5) is bonded to one O(14), one O(4), and two equivalent O(6) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-60°. In the sixth Fe site, Fe(6) is bonded to one O(13), one O(21), and two equivalent O(17) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 49-56°. In the seventh Fe site, Fe(7) is bonded to one O(10), one O(13), one O(15), one O(16), one O(18), and one O(20) atom to form FeO6 octahedra that share  a cornercorner with one Fe(6)O4 tetrahedra,  a cornercorner with one Fe(8)O4 tetrahedra, corners with two equivalent Fe(10)O4 tetrahedra, corners with two equivalent Fe(3)O4 tetrahedra, and edges with two equivalent Fe(7)O6 octahedra. In the eighth Fe site, Fe(8) is bonded to one O(11), one O(20), and two equivalent O(12) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 52-55°. In the ninth Fe site, Fe(9) is bonded to one O(17), one O(19), one O(21), one O(22), one O(23), and one O(24) atom to form FeO6 octahedra that share  a cornercorner with one Fe(10)O4 tetrahedra, corners with two equivalent Fe(12)O4 tetrahedra, corners with two equivalent Fe(6)O4 tetrahedra,  an edgeedge with one Fe(11)O6 octahedra, and edges with two equivalent Fe(9)O6 octahedra. In the tenth Fe site, Fe(10) is bonded to one O(16), one O(24), and two equivalent O(18) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-57°. In the eleventh Fe site, Fe(11) is bonded to one O(22), one O(3), two equivalent O(1), and two equivalent O(23) atoms to form FeO6 octahedra that share corners with three equivalent Fe(12)O4 tetrahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(9)O6 octahedra. In the twelfth Fe site, Fe(12) is bonded to one O(22), one O(8), and two equivalent O(23) atoms to form corner-sharing FeO4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-58°. There are twenty-four inequivalent O sites. In the first O site, O(1) is bonded in a water-like geometry to one Fe(1) and one Fe(11) atom. In the second O site, O(2) is bonded in a water-like geometry to two equivalent Fe(1) atoms. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Fe(11) and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded in a distorted rectangular see-saw-like geometry to one Fe(2), one Fe(5), and two equivalent Fe(1) atoms. In the fifth O site, O(5) is bonded in a water-like geometry to one Fe(2) and one Fe(4) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Fe(1), one Fe(2), and one Fe(5) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Fe(3) and two equivalent Fe(4) atoms. In the eighth O site, O(8) is bonded in a trigonal planar geometry to one Fe(12) and two equivalent Fe(1) atoms. In the ninth O site, O(9) is bonded in a distorted T-shaped geometry to one Fe(2) and two equivalent Fe(4) atoms. In the tenth O site, O(10) is bonded in a bent 120 degrees geometry to one Fe(3) and one Fe(7) atom. In the eleventh O site, O(11) is bonded in a trigonal planar geometry to one Fe(8) and two equivalent Fe(4) atoms. In the twelfth O site, O(12) is bonded in a bent 120 degrees geometry to one Fe(4) and one Fe(8) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal planar geometry to one Fe(6) and two equivalent Fe(7) atoms. In the fourteenth O site, O(14) is bonded in a distorted trigonal planar geometry to one Fe(5) and two equivalent Fe(4) atoms. In the fifteenth O site, O(15) is bonded in a trigonal planar geometry to one Fe(3) and two equivalent Fe(7) atoms. In the sixteenth O site, O(16) is bonded in a distorted trigonal planar geometry to one Fe(10) and two equivalent Fe(7) atoms. In the seventeenth O site, O(17) is bonded in a bent 120 degrees geometry to one Fe(6) and one Fe(9) atom. In the eighteenth O site, O(18) is bonded in a bent 120 degrees geometry to one Fe(10) and one Fe(7) atom. In the nineteenth O site, O(19) is bonded in a water-like geometry to two equivalent Fe(9) atoms. In the twentieth O site, O(20) is bonded in a distorted trigonal planar geometry to one Fe(8) and two equivalent Fe(7) atoms. In the twenty-first O site, O(21) is bonded in a distorted trigonal planar geometry to one Fe(6) and two equivalent Fe(9) atoms. In the twenty-second O site, O(22) is bonded in a distorted rectangular see-saw-like geometry to one Fe(11), one Fe(12), and two equivalent Fe(9) atoms. In the twenty-third O site, O(23) is bonded in a trigonal planar geometry to one Fe(11), one Fe(12), and one Fe(9) atom. In the twenty-fourth O site, O(24) is bonded in a trigonal planar geometry to one Fe(10) and two equivalent Fe(9) atoms. is represented by the Crystallographic Information File (CIF) [CIF]
data_FeO2
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.862
_cell_length_b   5.862
_cell_length_c   19.465
_cell_angle_alpha   81.085
_cell_angle_beta   81.085
_cell_angle_gamma   61.217
_symmetry_Int_Tables_number   1
_cell_volume   576.647
_cell_formula_units_Z   16
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  0.634  0.118  0.125  1.0
  Fe  Fe1  1  0.247  0.247  0.254  1.0
  Fe  Fe2  1  0.118  0.634  0.125  1.0
  Fe  Fe3  1  0.150  0.150  0.535  1.0
  Fe  Fe4  1  0.871  0.372  0.378  1.0
  Fe  Fe5  1  0.604  0.604  0.221  1.0
  Fe  Fe6  1  0.401  0.401  0.779  1.0
  Fe  Fe7  1  0.372  0.871  0.378  1.0
  Fe  Fe8  1  0.123  0.625  0.624  1.0
  Fe  Fe9  1  0.851  0.851  0.466  1.0
  Fe  Fe10  1  0.625  0.123  0.624  1.0
  Fe  Fe11  1  0.874  0.383  0.870  1.0
  Fe  Fe12  1  0.383  0.874  0.870  1.0
  Fe  Fe13  1  0.098  0.098  0.716  1.0
  Fe  Fe14  1  0.997  0.997  0.002  1.0
  Fe  Fe15  1  0.353  0.353  0.971  1.0
  O  O16  1  0.261  0.816  0.063  1.0
  O  O17  1  0.925  0.925  0.176  1.0
  O  O18  1  0.816  0.261  0.063  1.0
  O  O19  1  0.816  0.816  0.066  1.0
  O  O20  1  0.431  0.431  0.188  1.0
  O  O21  1  0.508  0.063  0.314  1.0
  O  O22  1  0.440  0.969  0.190  1.0
  O  O23  1  0.174  0.174  0.438  1.0
  O  O24  1  0.063  0.508  0.314  1.0
  O  O25  1  0.326  0.326  0.071  1.0
  O  O26  1  0.075  0.075  0.318  1.0
  O  O27  1  0.969  0.440  0.190  1.0
  O  O28  1  0.806  0.292  0.568  1.0
  O  O29  1  0.692  0.692  0.428  1.0
  O  O30  1  0.704  0.196  0.432  1.0
  O  O31  1  0.430  0.430  0.682  1.0
  O  O32  1  0.292  0.806  0.568  1.0
  O  O33  1  0.569  0.569  0.319  1.0
  O  O34  1  0.314  0.314  0.569  1.0
  O  O35  1  0.196  0.704  0.432  1.0
  O  O36  1  0.934  0.934  0.681  1.0
  O  O37  1  0.072  0.542  0.816  1.0
  O  O38  1  0.958  0.441  0.683  1.0
  O  O39  1  0.687  0.687  0.916  1.0
  O  O40  1  0.542  0.072  0.816  1.0
  O  O41  1  0.822  0.822  0.565  1.0
  O  O42  1  0.557  0.557  0.817  1.0
  O  O43  1  0.441  0.958  0.683  1.0
  O  O44  1  0.182  0.182  0.937  1.0
  O  O45  1  0.196  0.718  0.940  1.0
  O  O46  1  0.078  0.078  0.816  1.0
  O  O47  1  0.718  0.196  0.940  1.0
[/CIF]
.