Ca(FeO2)4 crystallizes in the monoclinic Cm space group. Ca(1) is bonded in a 4-coordinate geometry to two equivalent O(6) and two equivalent O(7) atoms. 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 a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 51-55°. 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 a mixture of distorted corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 51-60°. In the third Fe site, Fe(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 53-55°. 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 a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 53-60°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Fe(3) and two equivalent Fe(4) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Fe(1) and two equivalent Fe(3) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Fe(4) and two equivalent Fe(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Fe(2) and two equivalent Fe(1) atoms. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Fe(4) and two equivalent Fe(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Ca(1), one Fe(3), and two equivalent Fe(2) atoms to form a mixture of distorted corner and edge-sharing OCa2Fe3 trigonal bipyramids. In the seventh O site, O(7) is bonded to two equivalent Ca(1), one Fe(1), and two equivalent Fe(4) atoms to form a mixture of corner and edge-sharing OCa2Fe3 trigonal bipyramids. 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.
Ca(FeO2)4 crystallizes in the monoclinic Cm space group. Ca(1) is bonded in a 4-coordinate geometry to two equivalent O(6) and two equivalent O(7) atoms. Both Ca(1)-O(6) bond lengths are 2.35 Å. Both Ca(1)-O(7) bond lengths are 2.39 Å. 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 a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 51-55°. The Fe(1)-O(2) bond length is 1.92 Å. The Fe(1)-O(7) bond length is 2.02 Å. Both Fe(1)-O(4) bond lengths are 1.99 Å. Both Fe(1)-O(5) bond lengths are 2.05 Å. 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 a mixture of distorted corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 51-60°. The Fe(2)-O(4) bond length is 1.93 Å. The Fe(2)-O(8) bond length is 1.94 Å. Both Fe(2)-O(3) bond lengths are 1.97 Å. Both Fe(2)-O(6) bond lengths are 2.23 Å. In the third Fe site, Fe(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 53-55°. The Fe(3)-O(1) bond length is 1.90 Å. The Fe(3)-O(6) bond length is 1.98 Å. Both Fe(3)-O(2) bond lengths are 2.00 Å. Both Fe(3)-O(8) bond lengths are 2.02 Å. 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 a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedral tilt angles range from 53-60°. The Fe(4)-O(3) bond length is 1.97 Å. The Fe(4)-O(5) bond length is 1.98 Å. Both Fe(4)-O(1) bond lengths are 1.96 Å. Both Fe(4)-O(7) bond lengths are 2.15 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Fe(3) and two equivalent Fe(4) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Fe(1) and two equivalent Fe(3) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Fe(4) and two equivalent Fe(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Fe(2) and two equivalent Fe(1) atoms. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Fe(4) and two equivalent Fe(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Ca(1), one Fe(3), and two equivalent Fe(2) atoms to form a mixture of distorted corner and edge-sharing OCa2Fe3 trigonal bipyramids. In the seventh O site, O(7) is bonded to two equivalent Ca(1), one Fe(1), and two equivalent Fe(4) atoms to form a mixture of corner and edge-sharing OCa2Fe3 trigonal bipyramids. 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.