CaMn4O8 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a 5-coordinate geometry to one O(4), one O(5), one O(6), one O(7), and one O(8) atom. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(4), one O(5), and two equivalent O(6) atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 49-54°. In the second Mn site, Mn(2) is bonded to one O(1), one O(2), one O(3), one O(6), and two equivalent O(5) atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 51-55°. In the third Mn site, Mn(3) is bonded to one O(1), one O(3), one O(4), one O(8), and two equivalent O(7) atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 49-55°. In the fourth Mn site, Mn(4) is bonded to one O(2), one O(3), one O(4), one O(7), and two equivalent O(8) atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 51-54°. There are eight inequivalent O sites. In the first O site, O(5) is bonded to one Ca(1), one Mn(1), and two equivalent Mn(2) atoms to form a mixture of edge and corner-sharing OCaMn3 trigonal pyramids. In the second O site, O(6) is bonded to one Ca(1), one Mn(2), and two equivalent Mn(1) atoms to form a mixture of edge and corner-sharing OCaMn3 trigonal pyramids. In the third O site, O(7) is bonded to one Ca(1), one Mn(4), and two equivalent Mn(3) atoms to form a mixture of distorted edge and corner-sharing OCaMn3 trigonal pyramids. In the fourth O site, O(8) is bonded to one Ca(1), one Mn(3), and two equivalent Mn(4) atoms to form a mixture of distorted edge and corner-sharing OCaMn3 trigonal pyramids. In the fifth O site, O(1) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one Mn(3) atom. In the sixth O site, O(2) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one Mn(4) atom. In the seventh O site, O(3) is bonded in a trigonal planar geometry to one Mn(2), one Mn(3), and one Mn(4) atom. In the eighth O site, O(4) is bonded to one Ca(1), one Mn(1), one Mn(3), and one Mn(4) atom to form a mixture of distorted edge and corner-sharing OCaMn3 trigonal pyramids.
CaMn4O8 crystallizes in the monoclinic P2_1/c space group. Ca(1) is bonded in a 5-coordinate geometry to one O(4), one O(5), one O(6), one O(7), and one O(8) atom. The Ca(1)-O(4) bond length is 2.51 Å. The Ca(1)-O(5) bond length is 2.32 Å. The Ca(1)-O(6) bond length is 2.27 Å. The Ca(1)-O(7) bond length is 2.35 Å. The Ca(1)-O(8) bond length is 2.31 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(4), one O(5), and two equivalent O(6) atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 49-54°. The Mn(1)-O(1) bond length is 1.93 Å. The Mn(1)-O(2) bond length is 1.91 Å. The Mn(1)-O(4) bond length is 1.94 Å. The Mn(1)-O(5) bond length is 2.03 Å. There is one shorter (1.94 Å) and one longer (2.02 Å) Mn(1)-O(6) bond length. In the second Mn site, Mn(2) is bonded to one O(1), one O(2), one O(3), one O(6), and two equivalent O(5) atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 51-55°. The Mn(2)-O(1) bond length is 2.12 Å. The Mn(2)-O(2) bond length is 2.02 Å. The Mn(2)-O(3) bond length is 1.91 Å. The Mn(2)-O(6) bond length is 2.17 Å. There is one shorter (1.99 Å) and one longer (2.05 Å) Mn(2)-O(5) bond length. In the third Mn site, Mn(3) is bonded to one O(1), one O(3), one O(4), one O(8), and two equivalent O(7) atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 49-55°. The Mn(3)-O(1) bond length is 1.90 Å. The Mn(3)-O(3) bond length is 1.91 Å. The Mn(3)-O(4) bond length is 1.94 Å. The Mn(3)-O(8) bond length is 1.97 Å. There is one shorter (2.01 Å) and one longer (2.03 Å) Mn(3)-O(7) bond length. In the fourth Mn site, Mn(4) is bonded to one O(2), one O(3), one O(4), one O(7), and two equivalent O(8) atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 51-54°. The Mn(4)-O(2) bond length is 1.90 Å. The Mn(4)-O(3) bond length is 2.01 Å. The Mn(4)-O(4) bond length is 2.08 Å. The Mn(4)-O(7) bond length is 2.08 Å. There is one shorter (1.97 Å) and one longer (2.15 Å) Mn(4)-O(8) bond length. There are eight inequivalent O sites. In the first O site, O(5) is bonded to one Ca(1), one Mn(1), and two equivalent Mn(2) atoms to form a mixture of edge and corner-sharing OCaMn3 trigonal pyramids. In the second O site, O(6) is bonded to one Ca(1), one Mn(2), and two equivalent Mn(1) atoms to form a mixture of edge and corner-sharing OCaMn3 trigonal pyramids. In the third O site, O(7) is bonded to one Ca(1), one Mn(4), and two equivalent Mn(3) atoms to form a mixture of distorted edge and corner-sharing OCaMn3 trigonal pyramids. In the fourth O site, O(8) is bonded to one Ca(1), one Mn(3), and two equivalent Mn(4) atoms to form a mixture of distorted edge and corner-sharing OCaMn3 trigonal pyramids. In the fifth O site, O(1) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one Mn(3) atom. In the sixth O site, O(2) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one Mn(4) atom. In the seventh O site, O(3) is bonded in a trigonal planar geometry to one Mn(2), one Mn(3), and one Mn(4) atom. In the eighth O site, O(4) is bonded to one Ca(1), one Mn(1), one Mn(3), and one Mn(4) atom to form a mixture of distorted edge and corner-sharing OCaMn3 trigonal pyramids.