CaMnO2 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 distorted CaO6 octahedra that share corners with two equivalent Mn(1)O4 trigonal pyramids, edges with four equivalent Ca(1)O6 octahedra, and edges with three equivalent Mn(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 Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form MnO4 trigonal pyramids that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Mn(1)O4 trigonal pyramids, and edges with three equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 11-12°. In the second Mn site, Mn(2) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Ca(1), one Mn(2), and two equivalent Mn(1) atoms to form distorted OCa3Mn3 octahedra that share corners with two equivalent O(3)Ca4Mn square pyramids,  a cornercorner with one O(4)Ca2Mn2 tetrahedra, edges with four equivalent O(1)Ca3Mn3 octahedra, edges with three equivalent O(3)Ca4Mn square pyramids, and edges with two equivalent O(4)Ca2Mn2 tetrahedra. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(2), one Mn(1), and one Mn(2) atom. In the third O site, O(3) is bonded to two equivalent Ca(1), two equivalent Ca(2), and one Mn(1) atom to form OCa4Mn square pyramids that share corners with two equivalent O(1)Ca3Mn3 octahedra, corners with four equivalent O(4)Ca2Mn2 tetrahedra, edges with three equivalent O(1)Ca3Mn3 octahedra, and edges with two equivalent O(3)Ca4Mn square pyramids. The corner-sharing octahedral tilt angles are 13°. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), and two equivalent Mn(2) atoms to form OCa2Mn2 tetrahedra that share  a cornercorner with one O(1)Ca3Mn3 octahedra, corners with four equivalent O(3)Ca4Mn square pyramids, corners with two equivalent O(4)Ca2Mn2 tetrahedra, and edges with two equivalent O(1)Ca3Mn3 octahedra. The corner-sharing octahedral tilt angles are 10°.
CaMnO2 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 distorted CaO6 octahedra that share corners with two equivalent Mn(1)O4 trigonal pyramids, edges with four equivalent Ca(1)O6 octahedra, and edges with three equivalent Mn(1)O4 trigonal pyramids. The Ca(1)-O(4) bond length is 2.29 Å. There is one shorter (2.28 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 2.50-2.78 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 2.24 Å. There is one shorter (2.35 Å) and one longer (2.37 Å) Ca(2)-O(2) bond length. There is one shorter (2.43 Å) and one longer (2.47 Å) Ca(2)-O(3) bond length. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form MnO4 trigonal pyramids that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Mn(1)O4 trigonal pyramids, and edges with three equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 11-12°. The Mn(1)-O(2) bond length is 2.03 Å. The Mn(1)-O(3) bond length is 2.12 Å. There is one shorter (2.13 Å) and one longer (2.14 Å) Mn(1)-O(1) bond length. In the second Mn site, Mn(2) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), and two equivalent O(4) atoms. The Mn(2)-O(1) bond length is 2.25 Å. The Mn(2)-O(2) bond length is 2.00 Å. There is one shorter (2.06 Å) and one longer (2.10 Å) Mn(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 Mn(2), and two equivalent Mn(1) atoms to form distorted OCa3Mn3 octahedra that share corners with two equivalent O(3)Ca4Mn square pyramids,  a cornercorner with one O(4)Ca2Mn2 tetrahedra, edges with four equivalent O(1)Ca3Mn3 octahedra, edges with three equivalent O(3)Ca4Mn square pyramids, and edges with two equivalent O(4)Ca2Mn2 tetrahedra. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(2), one Mn(1), and one Mn(2) atom. In the third O site, O(3) is bonded to two equivalent Ca(1), two equivalent Ca(2), and one Mn(1) atom to form OCa4Mn square pyramids that share corners with two equivalent O(1)Ca3Mn3 octahedra, corners with four equivalent O(4)Ca2Mn2 tetrahedra, edges with three equivalent O(1)Ca3Mn3 octahedra, and edges with two equivalent O(3)Ca4Mn square pyramids. The corner-sharing octahedral tilt angles are 13°. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), and two equivalent Mn(2) atoms to form OCa2Mn2 tetrahedra that share  a cornercorner with one O(1)Ca3Mn3 octahedra, corners with four equivalent O(3)Ca4Mn square pyramids, corners with two equivalent O(4)Ca2Mn2 tetrahedra, and edges with two equivalent O(1)Ca3Mn3 octahedra. The corner-sharing octahedral tilt angles are 10°.