CaMn2O4 crystallizes in the monoclinic Cm space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), two equivalent O(6), and two equivalent O(7) atoms. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(5), and two equivalent O(8) atoms. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form MnO5 square pyramids that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, and edges with two equivalent Mn(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 52-58°. In the second Mn site, Mn(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O5 square pyramids, corners with two equivalent Mn(4)O5 square pyramids, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. In the third Mn site, Mn(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O5 square pyramids, corners with two equivalent Mn(4)O5 square pyramids, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. In the fourth Mn site, Mn(4) is bonded to one O(3), two equivalent O(1), and two equivalent O(7) atoms to form MnO5 square pyramids that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, and edges with two equivalent Mn(4)O5 square pyramids. The corner-sharing octahedral tilt angles range from 50-60°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mn(3) and two equivalent Mn(4) atoms. In the second O site, O(2) is bonded to one Ca(1), one Mn(1), and two equivalent Mn(3) atoms to form distorted OCaMn3 tetrahedra that share corners with two equivalent O(8)Ca2Mn3 square pyramids, corners with two equivalent O(2)CaMn3 tetrahedra,  an edgeedge with one O(8)Ca2Mn3 square pyramid, and edges with two equivalent O(6)Ca2Mn3 square pyramids. In the third O site, O(3) is bonded to one Ca(2), one Mn(4), and two equivalent Mn(2) atoms to form distorted OCaMn3 tetrahedra that share corners with two equivalent O(6)Ca2Mn3 square pyramids, corners with two equivalent O(3)CaMn3 tetrahedra,  an edgeedge with one O(6)Ca2Mn3 square pyramid, and edges with two equivalent O(8)Ca2Mn3 square pyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Mn(2), and two equivalent Mn(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(2) and two equivalent Mn(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Ca(1), one Mn(3), and two equivalent Mn(2) atoms to form distorted OCa2Mn3 square pyramids that share corners with two equivalent O(3)CaMn3 tetrahedra, edges with two equivalent O(6)Ca2Mn3 square pyramids, edges with two equivalent O(8)Ca2Mn3 square pyramids,  an edgeedge with one O(3)CaMn3 tetrahedra, and edges with two equivalent O(2)CaMn3 tetrahedra. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(1) and two equivalent Mn(4) atoms. In the eighth O site, O(8) is bonded to two equivalent Ca(2), one Mn(2), and two equivalent Mn(3) atoms to form OCa2Mn3 square pyramids that share corners with two equivalent O(2)CaMn3 tetrahedra, edges with two equivalent O(6)Ca2Mn3 square pyramids, edges with two equivalent O(8)Ca2Mn3 square pyramids,  an edgeedge with one O(2)CaMn3 tetrahedra, and edges with two equivalent O(3)CaMn3 tetrahedra.
CaMn2O4 crystallizes in the monoclinic Cm space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to one O(2), one O(4), two equivalent O(6), and two equivalent O(7) atoms. The Ca(1)-O(2) bond length is 2.57 Å. The Ca(1)-O(4) bond length is 2.67 Å. Both Ca(1)-O(6) bond lengths are 2.28 Å. Both Ca(1)-O(7) bond lengths are 2.30 Å. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(5), and two equivalent O(8) atoms. The Ca(2)-O(3) bond length is 2.38 Å. Both Ca(2)-O(5) bond lengths are 2.29 Å. Both Ca(2)-O(8) bond lengths are 2.27 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form MnO5 square pyramids that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, and edges with two equivalent Mn(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 52-58°. The Mn(1)-O(2) bond length is 2.14 Å. Both Mn(1)-O(4) bond lengths are 1.95 Å. Both Mn(1)-O(5) bond lengths are 2.04 Å. In the second Mn site, Mn(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O5 square pyramids, corners with two equivalent Mn(4)O5 square pyramids, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The Mn(2)-O(4) bond length is 2.22 Å. The Mn(2)-O(8) bond length is 2.31 Å. Both Mn(2)-O(3) bond lengths are 1.98 Å. Both Mn(2)-O(6) bond lengths are 2.02 Å. In the third Mn site, Mn(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(1)O5 square pyramids, corners with two equivalent Mn(4)O5 square pyramids, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The Mn(3)-O(1) bond length is 2.11 Å. The Mn(3)-O(6) bond length is 2.26 Å. Both Mn(3)-O(2) bond lengths are 1.98 Å. Both Mn(3)-O(8) bond lengths are 2.03 Å. In the fourth Mn site, Mn(4) is bonded to one O(3), two equivalent O(1), and two equivalent O(7) atoms to form MnO5 square pyramids that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, and edges with two equivalent Mn(4)O5 square pyramids. The corner-sharing octahedral tilt angles range from 50-60°. The Mn(4)-O(3) bond length is 2.14 Å. Both Mn(4)-O(1) bond lengths are 1.94 Å. Both Mn(4)-O(7) bond lengths are 2.03 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mn(3) and two equivalent Mn(4) atoms. In the second O site, O(2) is bonded to one Ca(1), one Mn(1), and two equivalent Mn(3) atoms to form distorted OCaMn3 tetrahedra that share corners with two equivalent O(8)Ca2Mn3 square pyramids, corners with two equivalent O(2)CaMn3 tetrahedra,  an edgeedge with one O(8)Ca2Mn3 square pyramid, and edges with two equivalent O(6)Ca2Mn3 square pyramids. In the third O site, O(3) is bonded to one Ca(2), one Mn(4), and two equivalent Mn(2) atoms to form distorted OCaMn3 tetrahedra that share corners with two equivalent O(6)Ca2Mn3 square pyramids, corners with two equivalent O(3)CaMn3 tetrahedra,  an edgeedge with one O(6)Ca2Mn3 square pyramid, and edges with two equivalent O(8)Ca2Mn3 square pyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ca(1), one Mn(2), and two equivalent Mn(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(2) and two equivalent Mn(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Ca(1), one Mn(3), and two equivalent Mn(2) atoms to form distorted OCa2Mn3 square pyramids that share corners with two equivalent O(3)CaMn3 tetrahedra, edges with two equivalent O(6)Ca2Mn3 square pyramids, edges with two equivalent O(8)Ca2Mn3 square pyramids,  an edgeedge with one O(3)CaMn3 tetrahedra, and edges with two equivalent O(2)CaMn3 tetrahedra. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(1) and two equivalent Mn(4) atoms. In the eighth O site, O(8) is bonded to two equivalent Ca(2), one Mn(2), and two equivalent Mn(3) atoms to form OCa2Mn3 square pyramids that share corners with two equivalent O(2)CaMn3 tetrahedra, edges with two equivalent O(6)Ca2Mn3 square pyramids, edges with two equivalent O(8)Ca2Mn3 square pyramids,  an edgeedge with one O(2)CaMn3 tetrahedra, and edges with two equivalent O(3)CaMn3 tetrahedra.