CaFeO2 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(4), two equivalent O(3), and three equivalent O(1) atoms to form CaO6 octahedra that share  a cornercorner with one Fe(2)O4 tetrahedra, corners with two equivalent Fe(1)O4 trigonal pyramids, edges with four equivalent Ca(1)O6 octahedra, edges with two equivalent Fe(2)O4 tetrahedra, and edges with three equivalent Fe(1)O4 trigonal pyramids. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(2), and two equivalent O(3) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form FeO4 trigonal pyramids that share corners with two equivalent Ca(1)O6 octahedra, corners with three equivalent Fe(2)O4 tetrahedra, corners with two equivalent Fe(1)O4 trigonal pyramids, and edges with three equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-11°. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), and two equivalent O(4) atoms to form distorted FeO4 tetrahedra that share  a cornercorner with one Ca(1)O6 octahedra, corners with two equivalent Fe(2)O4 tetrahedra, corners with three equivalent Fe(1)O4 trigonal pyramids, and edges with two equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles are 4°. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(1), one Fe(2), and two equivalent Fe(1) atoms to form OCa3Fe3 octahedra that share corners with two equivalent O(3)Ca4Fe square pyramids,  a cornercorner with one O(4)Ca2Fe2 tetrahedra, edges with four equivalent O(1)Ca3Fe3 octahedra, edges with three equivalent O(3)Ca4Fe square pyramids, and edges with two equivalent O(4)Ca2Fe2 tetrahedra. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(2), one Fe(1), and one Fe(2) atom. In the third O site, O(3) is bonded to two equivalent Ca(1), two equivalent Ca(2), and one Fe(1) atom to form OCa4Fe square pyramids that share corners with two equivalent O(1)Ca3Fe3 octahedra, corners with four equivalent O(4)Ca2Fe2 tetrahedra, edges with three equivalent O(1)Ca3Fe3 octahedra, and edges with two equivalent O(3)Ca4Fe square pyramids. The corner-sharing octahedral tilt angles range from 11-13°. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), and two equivalent Fe(2) atoms to form distorted OCa2Fe2 tetrahedra that share  a cornercorner with one O(1)Ca3Fe3 octahedra, corners with four equivalent O(3)Ca4Fe square pyramids, corners with two equivalent O(4)Ca2Fe2 tetrahedra, and edges with two equivalent O(1)Ca3Fe3 octahedra. The corner-sharing octahedral tilt angles are 17°.
CaFeO2 crystallizes in the triclinic P-1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(4), two equivalent O(3), and three equivalent O(1) atoms to form CaO6 octahedra that share  a cornercorner with one Fe(2)O4 tetrahedra, corners with two equivalent Fe(1)O4 trigonal pyramids, edges with four equivalent Ca(1)O6 octahedra, edges with two equivalent Fe(2)O4 tetrahedra, and edges with three equivalent Fe(1)O4 trigonal pyramids. The Ca(1)-O(4) bond length is 2.31 Å. There is one shorter (2.27 Å) and one longer (2.29 Å) Ca(1)-O(3) bond length. There are a spread of Ca(1)-O(1) bond distances ranging from 2.47-2.59 Å. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(2), and two equivalent O(3) atoms. The Ca(2)-O(4) bond length is 2.25 Å. There is one shorter (2.35 Å) and one longer (2.43 Å) Ca(2)-O(2) bond length. Both Ca(2)-O(3) bond lengths are 2.41 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form FeO4 trigonal pyramids that share corners with two equivalent Ca(1)O6 octahedra, corners with three equivalent Fe(2)O4 tetrahedra, corners with two equivalent Fe(1)O4 trigonal pyramids, and edges with three equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 10-11°. The Fe(1)-O(2) bond length is 1.96 Å. The Fe(1)-O(3) bond length is 2.15 Å. There is one shorter (2.04 Å) and one longer (2.20 Å) Fe(1)-O(1) bond length. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), and two equivalent O(4) atoms to form distorted FeO4 tetrahedra that share  a cornercorner with one Ca(1)O6 octahedra, corners with two equivalent Fe(2)O4 tetrahedra, corners with three equivalent Fe(1)O4 trigonal pyramids, and edges with two equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles are 4°. The Fe(2)-O(1) bond length is 2.25 Å. The Fe(2)-O(2) bond length is 1.93 Å. There is one shorter (1.96 Å) and one longer (2.10 Å) Fe(2)-O(4) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(1), one Fe(2), and two equivalent Fe(1) atoms to form OCa3Fe3 octahedra that share corners with two equivalent O(3)Ca4Fe square pyramids,  a cornercorner with one O(4)Ca2Fe2 tetrahedra, edges with four equivalent O(1)Ca3Fe3 octahedra, edges with three equivalent O(3)Ca4Fe square pyramids, and edges with two equivalent O(4)Ca2Fe2 tetrahedra. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(2), one Fe(1), and one Fe(2) atom. In the third O site, O(3) is bonded to two equivalent Ca(1), two equivalent Ca(2), and one Fe(1) atom to form OCa4Fe square pyramids that share corners with two equivalent O(1)Ca3Fe3 octahedra, corners with four equivalent O(4)Ca2Fe2 tetrahedra, edges with three equivalent O(1)Ca3Fe3 octahedra, and edges with two equivalent O(3)Ca4Fe square pyramids. The corner-sharing octahedral tilt angles range from 11-13°. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), and two equivalent Fe(2) atoms to form distorted OCa2Fe2 tetrahedra that share  a cornercorner with one O(1)Ca3Fe3 octahedra, corners with four equivalent O(3)Ca4Fe square pyramids, corners with two equivalent O(4)Ca2Fe2 tetrahedra, and edges with two equivalent O(1)Ca3Fe3 octahedra. The corner-sharing octahedral tilt angles are 17°.