Ca8Mn8O23 crystallizes in the tetragonal P4/mmm space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a distorted q6 geometry to one O(4), two equivalent O(2), four equivalent O(6), and four equivalent O(7) atoms. In the second Ca site, Ca(2) is bonded to one O(1), one O(5), two equivalent O(3), four equivalent O(6), and four equivalent O(7) atoms to form CaO12 cuboctahedra that share corners with four equivalent Ca(2)O12 cuboctahedra, faces with four equivalent Ca(2)O12 cuboctahedra, faces with two equivalent Mn(3)O6 octahedra, faces with four equivalent Mn(2)O6 octahedra, and faces with two equivalent Mn(1)O5 square pyramids. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1) and four equivalent O(6) atoms to form MnO5 square pyramids that share corners with four equivalent Mn(2)O6 octahedra,  a cornercorner with one Mn(1)O5 square pyramid, and faces with four equivalent Ca(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 16°. In the second Mn site, Mn(2) is bonded to one O(2), one O(3), two equivalent O(6), and two equivalent O(7) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(1)O5 square pyramids, and faces with four equivalent Ca(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-5°. In the third Mn site, Mn(3) is bonded to one O(4), one O(5), and four equivalent O(7) atoms to form MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with four equivalent Mn(2)O6 octahedra, and faces with four equivalent Ca(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-5°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to four equivalent Ca(2) and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to four equivalent Ca(1) and two equivalent Mn(2) atoms. In the third O site, O(3) is bonded to four equivalent Ca(2) and two equivalent Mn(2) atoms to form a mixture of distorted face, corner, and edge-sharing OCa4Mn2 octahedra. The corner-sharing octahedral tilt angles range from 7-57°. In the fourth O site, O(4) is bonded to four equivalent Ca(1) and two equivalent Mn(3) atoms to form a mixture of distorted face and corner-sharing OCa4Mn2 octahedra. The corner-sharing octahedra are not tilted. In the fifth O site, O(5) is bonded to four equivalent Ca(2) and two equivalent Mn(3) atoms to form a mixture of distorted face, corner, and edge-sharing OCa4Mn2 octahedra. The corner-sharing octahedra are not tilted. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Mn(1), and one Mn(2) atom. In the seventh O site, O(7) is bonded to two equivalent Ca(1), two equivalent Ca(2), one Mn(2), and one Mn(3) atom to form a mixture of distorted face, corner, and edge-sharing OCa4Mn2 octahedra. The corner-sharing octahedral tilt angles range from 5-57°.
Ca8Mn8O23 crystallizes in the tetragonal P4/mmm space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a distorted q6 geometry to one O(4), two equivalent O(2), four equivalent O(6), and four equivalent O(7) atoms. The Ca(1)-O(4) bond length is 2.63 Å. Both Ca(1)-O(2) bond lengths are 2.69 Å. All Ca(1)-O(6) bond lengths are 2.57 Å. All Ca(1)-O(7) bond lengths are 2.72 Å. In the second Ca site, Ca(2) is bonded to one O(1), one O(5), two equivalent O(3), four equivalent O(6), and four equivalent O(7) atoms to form CaO12 cuboctahedra that share corners with four equivalent Ca(2)O12 cuboctahedra, faces with four equivalent Ca(2)O12 cuboctahedra, faces with two equivalent Mn(3)O6 octahedra, faces with four equivalent Mn(2)O6 octahedra, and faces with two equivalent Mn(1)O5 square pyramids. The Ca(2)-O(1) bond length is 2.85 Å. The Ca(2)-O(5) bond length is 2.54 Å. Both Ca(2)-O(3) bond lengths are 2.70 Å. All Ca(2)-O(6) bond lengths are 2.96 Å. All Ca(2)-O(7) bond lengths are 2.58 Å. There are three inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1) and four equivalent O(6) atoms to form MnO5 square pyramids that share corners with four equivalent Mn(2)O6 octahedra,  a cornercorner with one Mn(1)O5 square pyramid, and faces with four equivalent Ca(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 16°. The Mn(1)-O(1) bond length is 1.85 Å. All Mn(1)-O(6) bond lengths are 1.90 Å. In the second Mn site, Mn(2) is bonded to one O(2), one O(3), two equivalent O(6), and two equivalent O(7) atoms to form MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(1)O5 square pyramids, and faces with four equivalent Ca(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-5°. The Mn(2)-O(2) bond length is 1.89 Å. The Mn(2)-O(3) bond length is 1.95 Å. Both Mn(2)-O(6) bond lengths are 1.95 Å. Both Mn(2)-O(7) bond lengths are 1.91 Å. In the third Mn site, Mn(3) is bonded to one O(4), one O(5), and four equivalent O(7) atoms to form MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with four equivalent Mn(2)O6 octahedra, and faces with four equivalent Ca(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-5°. The Mn(3)-O(4) bond length is 1.91 Å. The Mn(3)-O(5) bond length is 1.93 Å. All Mn(3)-O(7) bond lengths are 1.90 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to four equivalent Ca(2) and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to four equivalent Ca(1) and two equivalent Mn(2) atoms. In the third O site, O(3) is bonded to four equivalent Ca(2) and two equivalent Mn(2) atoms to form a mixture of distorted face, corner, and edge-sharing OCa4Mn2 octahedra. The corner-sharing octahedral tilt angles range from 7-57°. In the fourth O site, O(4) is bonded to four equivalent Ca(1) and two equivalent Mn(3) atoms to form a mixture of distorted face and corner-sharing OCa4Mn2 octahedra. The corner-sharing octahedra are not tilted. In the fifth O site, O(5) is bonded to four equivalent Ca(2) and two equivalent Mn(3) atoms to form a mixture of distorted face, corner, and edge-sharing OCa4Mn2 octahedra. The corner-sharing octahedra are not tilted. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to two equivalent Ca(1), two equivalent Ca(2), one Mn(1), and one Mn(2) atom. In the seventh O site, O(7) is bonded to two equivalent Ca(1), two equivalent Ca(2), one Mn(2), and one Mn(3) atom to form a mixture of distorted face, corner, and edge-sharing OCa4Mn2 octahedra. The corner-sharing octahedral tilt angles range from 5-57°.