CaMn4O8 crystallizes in the monoclinic Cm space group. Ca(1) is bonded in a 4-coordinate geometry to two equivalent O(6) and two equivalent O(7) atoms. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form a mixture of corner and edge-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 51-54°. 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 a mixture of corner and edge-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(6), two equivalent O(2), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 53-54°. In the fourth Mn site, Mn(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 53-55°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mn(3) and two equivalent Mn(4) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mn(1) and two equivalent Mn(3) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Mn(4) and two equivalent Mn(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mn(2) and two equivalent Mn(1) atoms. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Mn(4) 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 a mixture of distorted corner and edge-sharing OCa2Mn3 trigonal bipyramids. In the seventh O site, O(7) is bonded to two equivalent Ca(1), one Mn(1), and two equivalent Mn(4) atoms to form a mixture of distorted corner and edge-sharing OCa2Mn3 trigonal bipyramids. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Mn(2) and two equivalent Mn(3) atoms.
CaMn4O8 crystallizes in the monoclinic Cm space group. Ca(1) is bonded in a 4-coordinate geometry to two equivalent O(6) and two equivalent O(7) atoms. Both Ca(1)-O(6) bond lengths are 2.33 Å. Both Ca(1)-O(7) bond lengths are 2.40 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form a mixture of corner and edge-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 51-54°. The Mn(1)-O(2) bond length is 1.91 Å. The Mn(1)-O(7) bond length is 2.03 Å. Both Mn(1)-O(4) bond lengths are 1.97 Å. Both Mn(1)-O(5) bond lengths are 2.02 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 a mixture of corner and edge-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 51-55°. The Mn(2)-O(4) bond length is 1.93 Å. The Mn(2)-O(8) bond length is 1.93 Å. Both Mn(2)-O(3) bond lengths are 1.95 Å. Both Mn(2)-O(6) bond lengths are 2.16 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 a mixture of corner and edge-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 53-54°. The Mn(3)-O(1) bond length is 1.89 Å. The Mn(3)-O(6) bond length is 2.00 Å. Both Mn(3)-O(2) bond lengths are 1.99 Å. Both Mn(3)-O(8) bond lengths are 2.02 Å. In the fourth Mn site, Mn(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles range from 53-55°. The Mn(4)-O(3) bond length is 1.91 Å. The Mn(4)-O(5) bond length is 1.99 Å. Both Mn(4)-O(1) bond lengths are 1.94 Å. Both Mn(4)-O(7) bond lengths are 2.13 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Mn(3) and two equivalent Mn(4) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mn(1) and two equivalent Mn(3) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Mn(4) and two equivalent Mn(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mn(2) and two equivalent Mn(1) atoms. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Mn(4) 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 a mixture of distorted corner and edge-sharing OCa2Mn3 trigonal bipyramids. In the seventh O site, O(7) is bonded to two equivalent Ca(1), one Mn(1), and two equivalent Mn(4) atoms to form a mixture of distorted corner and edge-sharing OCa2Mn3 trigonal bipyramids. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Mn(2) and two equivalent Mn(3) atoms.