Ca4Mn2O7 crystallizes in the orthorhombic Cmce space group. Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), and five equivalent O(3) atoms. Mn(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing MnO5 trigonal bipyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Ca(1) and two equivalent Mn(1) atoms to form OCa4Mn2 octahedra that share corners with twelve equivalent O(3)Ca5Mn octahedra, corners with four equivalent O(2)Ca2Mn2 tetrahedra, edges with two equivalent O(2)Ca2Mn2 tetrahedra, and faces with four equivalent O(3)Ca5Mn octahedra. The corner-sharing octahedral tilt angles range from 40-62°. In the second O site, O(2) is bonded to two equivalent Ca(1) and two equivalent Mn(1) atoms to form distorted OCa2Mn2 tetrahedra that share corners with two equivalent O(1)Ca4Mn2 octahedra, corners with six equivalent O(3)Ca5Mn octahedra, corners with two equivalent O(2)Ca2Mn2 tetrahedra,  an edgeedge with one O(1)Ca4Mn2 octahedra, and edges with four equivalent O(3)Ca5Mn octahedra. The corner-sharing octahedral tilt angles range from 19-77°. In the third O site, O(3) is bonded to five equivalent Ca(1) and one Mn(1) atom to form distorted OCa5Mn octahedra that share corners with three equivalent O(1)Ca4Mn2 octahedra, corners with five equivalent O(3)Ca5Mn octahedra, corners with three equivalent O(2)Ca2Mn2 tetrahedra, edges with eight equivalent O(3)Ca5Mn octahedra, edges with two equivalent O(2)Ca2Mn2 tetrahedra, and  a faceface with one O(1)Ca4Mn2 octahedra. The corner-sharing octahedral tilt angles range from 3-62°.
Ca4Mn2O7 crystallizes in the orthorhombic Cmce space group. Ca(1) is bonded in a 7-coordinate geometry to one O(1), one O(2), and five equivalent O(3) atoms. The Ca(1)-O(1) bond length is 2.53 Å. The Ca(1)-O(2) bond length is 2.29 Å. There are a spread of Ca(1)-O(3) bond distances ranging from 2.31-2.89 Å. Mn(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing MnO5 trigonal bipyramids. The Mn(1)-O(1) bond length is 1.92 Å. There is one shorter (1.87 Å) and one longer (2.08 Å) Mn(1)-O(2) bond length. Both Mn(1)-O(3) bond lengths are 1.99 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Ca(1) and two equivalent Mn(1) atoms to form OCa4Mn2 octahedra that share corners with twelve equivalent O(3)Ca5Mn octahedra, corners with four equivalent O(2)Ca2Mn2 tetrahedra, edges with two equivalent O(2)Ca2Mn2 tetrahedra, and faces with four equivalent O(3)Ca5Mn octahedra. The corner-sharing octahedral tilt angles range from 40-62°. In the second O site, O(2) is bonded to two equivalent Ca(1) and two equivalent Mn(1) atoms to form distorted OCa2Mn2 tetrahedra that share corners with two equivalent O(1)Ca4Mn2 octahedra, corners with six equivalent O(3)Ca5Mn octahedra, corners with two equivalent O(2)Ca2Mn2 tetrahedra,  an edgeedge with one O(1)Ca4Mn2 octahedra, and edges with four equivalent O(3)Ca5Mn octahedra. The corner-sharing octahedral tilt angles range from 19-77°. In the third O site, O(3) is bonded to five equivalent Ca(1) and one Mn(1) atom to form distorted OCa5Mn octahedra that share corners with three equivalent O(1)Ca4Mn2 octahedra, corners with five equivalent O(3)Ca5Mn octahedra, corners with three equivalent O(2)Ca2Mn2 tetrahedra, edges with eight equivalent O(3)Ca5Mn octahedra, edges with two equivalent O(2)Ca2Mn2 tetrahedra, and  a faceface with one O(1)Ca4Mn2 octahedra. The corner-sharing octahedral tilt angles range from 3-62°.