Mg(FeO2)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Fe(4)O6 octahedra, and  a faceface with one Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles are 42°. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form distorted FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-49°. In the second Fe site, Fe(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form distorted FeO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Fe(4)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-50°. In the third Fe site, Fe(3) is bonded in a 6-coordinate geometry to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms. In the fourth Fe site, Fe(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(3), and two equivalent Fe(4) atoms to form OMgFe3 trigonal pyramids that share  a cornercorner with one O(4)MgFe3 trigonal pyramid, corners with two equivalent O(1)MgFe3 trigonal pyramids, and edges with two equivalent O(3)Mg2Fe3 trigonal bipyramids. In the second O site, O(2) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Fe(1), and two equivalent Fe(3) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1), one Fe(4), and two equivalent Fe(2) atoms to form distorted OMg2Fe3 trigonal bipyramids that share edges with two equivalent O(3)Mg2Fe3 trigonal bipyramids, edges with two equivalent O(1)MgFe3 trigonal pyramids, and edges with two equivalent O(4)MgFe3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Mg(1), one Fe(2), and two equivalent Fe(1) atoms to form distorted OMgFe3 trigonal pyramids that share  a cornercorner with one O(1)MgFe3 trigonal pyramid, corners with two equivalent O(4)MgFe3 trigonal pyramids, and edges with two equivalent O(3)Mg2Fe3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(4) and two equivalent Fe(1) atoms. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Fe(3) and two equivalent Fe(2) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1) and two equivalent Fe(4) atoms. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Fe(2) and two equivalent Fe(3) atoms.
Mg(FeO2)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Fe(4)O6 octahedra, and  a faceface with one Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles are 42°. The Mg(1)-O(1) bond length is 2.01 Å. The Mg(1)-O(4) bond length is 2.00 Å. Both Mg(1)-O(2) bond lengths are 2.06 Å. There is one shorter (2.09 Å) and one longer (2.15 Å) Mg(1)-O(3) bond length. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form distorted FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-49°. The Fe(1)-O(2) bond length is 2.49 Å. The Fe(1)-O(7) bond length is 2.01 Å. Both Fe(1)-O(4) bond lengths are 2.00 Å. There is one shorter (1.93 Å) and one longer (1.94 Å) Fe(1)-O(5) bond length. In the second Fe site, Fe(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form distorted FeO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, corners with two equivalent Fe(4)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and  a faceface with one Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-50°. The Fe(2)-O(4) bond length is 2.21 Å. The Fe(2)-O(8) bond length is 2.01 Å. There is one shorter (2.09 Å) and one longer (2.18 Å) Fe(2)-O(3) bond length. There is one shorter (1.96 Å) and one longer (1.97 Å) Fe(2)-O(6) bond length. In the third Fe site, Fe(3) is bonded in a 6-coordinate geometry to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms. The Fe(3)-O(1) bond length is 2.05 Å. The Fe(3)-O(6) bond length is 1.93 Å. There is one shorter (1.92 Å) and one longer (2.50 Å) Fe(3)-O(2) bond length. There is one shorter (1.89 Å) and one longer (1.98 Å) Fe(3)-O(8) bond length. In the fourth Fe site, Fe(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Fe(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, and edges with two equivalent Fe(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. The Fe(4)-O(3) bond length is 2.24 Å. The Fe(4)-O(5) bond length is 2.08 Å. There is one shorter (2.01 Å) and one longer (2.06 Å) Fe(4)-O(1) bond length. There is one shorter (1.94 Å) and one longer (1.95 Å) Fe(4)-O(7) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Fe(3), and two equivalent Fe(4) atoms to form OMgFe3 trigonal pyramids that share  a cornercorner with one O(4)MgFe3 trigonal pyramid, corners with two equivalent O(1)MgFe3 trigonal pyramids, and edges with two equivalent O(3)Mg2Fe3 trigonal bipyramids. In the second O site, O(2) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Fe(1), and two equivalent Fe(3) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1), one Fe(4), and two equivalent Fe(2) atoms to form distorted OMg2Fe3 trigonal bipyramids that share edges with two equivalent O(3)Mg2Fe3 trigonal bipyramids, edges with two equivalent O(1)MgFe3 trigonal pyramids, and edges with two equivalent O(4)MgFe3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Mg(1), one Fe(2), and two equivalent Fe(1) atoms to form distorted OMgFe3 trigonal pyramids that share  a cornercorner with one O(1)MgFe3 trigonal pyramid, corners with two equivalent O(4)MgFe3 trigonal pyramids, and edges with two equivalent O(3)Mg2Fe3 trigonal bipyramids. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(4) and two equivalent Fe(1) atoms. In the sixth O site, O(6) is bonded in a distorted trigonal non-coplanar geometry to one Fe(3) and two equivalent Fe(2) atoms. In the seventh O site, O(7) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1) and two equivalent Fe(4) atoms. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Fe(2) and two equivalent Fe(3) atoms.