SrCa7Mn6Al2O21 crystallizes in the orthorhombic Amm2 space group. Sr(1) is bonded in a distorted q6 geometry to one O(3), two equivalent O(1), four equivalent O(4), and four equivalent O(5) atoms. There are five inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a distorted q6 geometry to two equivalent O(2), four equivalent O(4), and four equivalent O(5) atoms. In the second Ca site, Ca(2) is bonded in a distorted q6 geometry to one O(3), two equivalent O(1), two equivalent O(4), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. In the third Ca site, Ca(3) is bonded in a distorted q6 geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. In the fourth Ca site, Ca(4) is bonded in a distorted q6 geometry to one O(3), two equivalent O(1), four equivalent O(6), and four equivalent O(7) atoms. In the fifth Ca site, Ca(5) is bonded in a distorted q6 geometry to two equivalent O(2), four equivalent O(6), and four equivalent O(7) atoms. There are two 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), one O(6), and one O(7) atom to form MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra and corners with two equivalent Mn(2)O5 square pyramids. The corner-sharing octahedral tilt angles range from 0-2°. In the second Mn site, Mn(2) is bonded to one O(3), two equivalent O(5), and two equivalent O(7) atoms to form MnO5 square pyramids that share corners with four equivalent Mn(1)O6 octahedra and  a cornercorner with one Mn(2)O5 square pyramid. The corner-sharing octahedral tilt angles are 9°. Al(1) is bonded in a rectangular see-saw-like geometry to two equivalent O(4) and two equivalent O(6) atoms. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Sr(1), one Ca(4), two equivalent Ca(2), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to one Ca(1), one Ca(5), two equivalent Ca(3), and two equivalent Mn(1) atoms. In the third O site, O(3) is bonded to one Sr(1), one Ca(4), two equivalent Ca(2), and two equivalent Mn(2) atoms to form distorted OSrCa3Mn2 octahedra that share corners with eight equivalent O(6)Ca4MnAl octahedra, corners with eight equivalent O(4)SrCa3MnAl octahedra, faces with four equivalent O(7)Ca4Mn2 octahedra, and faces with four equivalent O(5)SrCa3Mn2 octahedra. The corner-sharing octahedral tilt angles range from 55-56°. In the fourth O site, O(4) is bonded to one Sr(1), one Ca(1), one Ca(2), one Ca(3), one Mn(1), and one Al(1) atom to form distorted OSrCa3MnAl octahedra that share corners with two equivalent O(7)Ca4Mn2 octahedra, corners with two equivalent O(3)SrCa3Mn2 octahedra, corners with two equivalent O(4)SrCa3MnAl octahedra, corners with four equivalent O(6)Ca4MnAl octahedra, corners with six equivalent O(5)SrCa3Mn2 octahedra, edges with two equivalent O(5)SrCa3Mn2 octahedra, edges with two equivalent O(4)SrCa3MnAl octahedra,  a faceface with one O(7)Ca4Mn2 octahedra,  a faceface with one O(6)Ca4MnAl octahedra,  a faceface with one O(5)SrCa3Mn2 octahedra, and  a faceface with one O(4)SrCa3MnAl octahedra. The corner-sharing octahedral tilt angles range from 1-70°. In the fifth O site, O(5) is bonded to one Sr(1), one Ca(1), one Ca(2), one Ca(3), one Mn(1), and one Mn(2) atom to form distorted OSrCa3Mn2 octahedra that share corners with two equivalent O(6)Ca4MnAl octahedra, corners with two equivalent O(5)SrCa3Mn2 octahedra, corners with four equivalent O(7)Ca4Mn2 octahedra, corners with six equivalent O(4)SrCa3MnAl octahedra, edges with two equivalent O(5)SrCa3Mn2 octahedra, edges with two equivalent O(4)SrCa3MnAl octahedra,  a faceface with one O(7)Ca4Mn2 octahedra,  a faceface with one O(6)Ca4MnAl octahedra,  a faceface with one O(3)SrCa3Mn2 octahedra,  a faceface with one O(5)SrCa3Mn2 octahedra, and  a faceface with one O(4)SrCa3MnAl octahedra. The corner-sharing octahedral tilt angles range from 3-66°. In the sixth O site, O(6) is bonded to one Ca(2), one Ca(3), one Ca(4), one Ca(5), one Mn(1), and one Al(1) atom to form distorted OCa4MnAl octahedra that share corners with two equivalent O(6)Ca4MnAl octahedra, corners with two equivalent O(3)SrCa3Mn2 octahedra, corners with two equivalent O(5)SrCa3Mn2 octahedra, corners with four equivalent O(4)SrCa3MnAl octahedra, corners with six equivalent O(7)Ca4Mn2 octahedra, edges with two equivalent O(7)Ca4Mn2 octahedra, edges with two equivalent O(6)Ca4MnAl octahedra,  a faceface with one O(7)Ca4Mn2 octahedra,  a faceface with one O(6)Ca4MnAl octahedra,  a faceface with one O(5)SrCa3Mn2 octahedra, and  a faceface with one O(4)SrCa3MnAl octahedra. The corner-sharing octahedral tilt angles range from 1-70°. In the seventh O site, O(7) is bonded to one Ca(2), one Ca(3), one Ca(4), one Ca(5), one Mn(1), and one Mn(2) atom to form distorted OCa4Mn2 octahedra that share corners with two equivalent O(7)Ca4Mn2 octahedra, corners with two equivalent O(4)SrCa3MnAl octahedra, corners with four equivalent O(5)SrCa3Mn2 octahedra, corners with six equivalent O(6)Ca4MnAl octahedra, edges with two equivalent O(7)Ca4Mn2 octahedra, edges with two equivalent O(6)Ca4MnAl octahedra,  a faceface with one O(7)Ca4Mn2 octahedra,  a faceface with one O(6)Ca4MnAl octahedra,  a faceface with one O(3)SrCa3Mn2 octahedra,  a faceface with one O(5)SrCa3Mn2 octahedra, and  a faceface with one O(4)SrCa3MnAl octahedra. The corner-sharing octahedral tilt angles range from 3-65°.
SrCa7Mn6Al2O21 crystallizes in the orthorhombic Amm2 space group. Sr(1) is bonded in a distorted q6 geometry to one O(3), two equivalent O(1), four equivalent O(4), and four equivalent O(5) atoms. The Sr(1)-O(3) bond length is 2.70 Å. Both Sr(1)-O(1) bond lengths are 2.77 Å. All Sr(1)-O(4) bond lengths are 2.77 Å. All Sr(1)-O(5) bond lengths are 2.79 Å. There are five inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a distorted q6 geometry to two equivalent O(2), four equivalent O(4), and four equivalent O(5) atoms. Both Ca(1)-O(2) bond lengths are 2.75 Å. All Ca(1)-O(4) bond lengths are 2.70 Å. All Ca(1)-O(5) bond lengths are 2.57 Å. In the second Ca site, Ca(2) is bonded in a distorted q6 geometry to one O(3), two equivalent O(1), two equivalent O(4), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. The Ca(2)-O(3) bond length is 2.61 Å. There is one shorter (2.72 Å) and one longer (2.76 Å) Ca(2)-O(1) bond length. Both Ca(2)-O(4) bond lengths are 2.77 Å. Both Ca(2)-O(5) bond lengths are 2.74 Å. Both Ca(2)-O(6) bond lengths are 2.77 Å. Both Ca(2)-O(7) bond lengths are 2.75 Å. In the third Ca site, Ca(3) is bonded in a distorted q6 geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. There is one shorter (2.74 Å) and one longer (2.75 Å) Ca(3)-O(2) bond length. Both Ca(3)-O(4) bond lengths are 2.67 Å. Both Ca(3)-O(5) bond lengths are 2.55 Å. Both Ca(3)-O(6) bond lengths are 2.71 Å. Both Ca(3)-O(7) bond lengths are 2.57 Å. In the fourth Ca site, Ca(4) is bonded in a distorted q6 geometry to one O(3), two equivalent O(1), four equivalent O(6), and four equivalent O(7) atoms. The Ca(4)-O(3) bond length is 2.57 Å. Both Ca(4)-O(1) bond lengths are 2.71 Å. All Ca(4)-O(6) bond lengths are 2.76 Å. All Ca(4)-O(7) bond lengths are 2.74 Å. In the fifth Ca site, Ca(5) is bonded in a distorted q6 geometry to two equivalent O(2), four equivalent O(6), and four equivalent O(7) atoms. Both Ca(5)-O(2) bond lengths are 2.73 Å. All Ca(5)-O(6) bond lengths are 2.70 Å. All Ca(5)-O(7) bond lengths are 2.56 Å. There are two 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), one O(6), and one O(7) atom to form MnO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra and corners with two equivalent Mn(2)O5 square pyramids. The corner-sharing octahedral tilt angles range from 0-2°. The Mn(1)-O(1) bond length is 1.89 Å. The Mn(1)-O(2) bond length is 1.84 Å. The Mn(1)-O(4) bond length is 2.07 Å. The Mn(1)-O(5) bond length is 1.99 Å. The Mn(1)-O(6) bond length is 2.05 Å. The Mn(1)-O(7) bond length is 1.98 Å. In the second Mn site, Mn(2) is bonded to one O(3), two equivalent O(5), and two equivalent O(7) atoms to form MnO5 square pyramids that share corners with four equivalent Mn(1)O6 octahedra and  a cornercorner with one Mn(2)O5 square pyramid. The corner-sharing octahedral tilt angles are 9°. The Mn(2)-O(3) bond length is 1.88 Å. Both Mn(2)-O(5) bond lengths are 1.90 Å. Both Mn(2)-O(7) bond lengths are 1.89 Å. Al(1) is bonded in a rectangular see-saw-like geometry to two equivalent O(4) and two equivalent O(6) atoms. Both Al(1)-O(4) bond lengths are 1.82 Å. Both Al(1)-O(6) bond lengths are 1.81 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Sr(1), one Ca(4), two equivalent Ca(2), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to one Ca(1), one Ca(5), two equivalent Ca(3), and two equivalent Mn(1) atoms. In the third O site, O(3) is bonded to one Sr(1), one Ca(4), two equivalent Ca(2), and two equivalent Mn(2) atoms to form distorted OSrCa3Mn2 octahedra that share corners with eight equivalent O(6)Ca4MnAl octahedra, corners with eight equivalent O(4)SrCa3MnAl octahedra, faces with four equivalent O(7)Ca4Mn2 octahedra, and faces with four equivalent O(5)SrCa3Mn2 octahedra. The corner-sharing octahedral tilt angles range from 55-56°. In the fourth O site, O(4) is bonded to one Sr(1), one Ca(1), one Ca(2), one Ca(3), one Mn(1), and one Al(1) atom to form distorted OSrCa3MnAl octahedra that share corners with two equivalent O(7)Ca4Mn2 octahedra, corners with two equivalent O(3)SrCa3Mn2 octahedra, corners with two equivalent O(4)SrCa3MnAl octahedra, corners with four equivalent O(6)Ca4MnAl octahedra, corners with six equivalent O(5)SrCa3Mn2 octahedra, edges with two equivalent O(5)SrCa3Mn2 octahedra, edges with two equivalent O(4)SrCa3MnAl octahedra,  a faceface with one O(7)Ca4Mn2 octahedra,  a faceface with one O(6)Ca4MnAl octahedra,  a faceface with one O(5)SrCa3Mn2 octahedra, and  a faceface with one O(4)SrCa3MnAl octahedra. The corner-sharing octahedral tilt angles range from 1-70°. In the fifth O site, O(5) is bonded to one Sr(1), one Ca(1), one Ca(2), one Ca(3), one Mn(1), and one Mn(2) atom to form distorted OSrCa3Mn2 octahedra that share corners with two equivalent O(6)Ca4MnAl octahedra, corners with two equivalent O(5)SrCa3Mn2 octahedra, corners with four equivalent O(7)Ca4Mn2 octahedra, corners with six equivalent O(4)SrCa3MnAl octahedra, edges with two equivalent O(5)SrCa3Mn2 octahedra, edges with two equivalent O(4)SrCa3MnAl octahedra,  a faceface with one O(7)Ca4Mn2 octahedra,  a faceface with one O(6)Ca4MnAl octahedra,  a faceface with one O(3)SrCa3Mn2 octahedra,  a faceface with one O(5)SrCa3Mn2 octahedra, and  a faceface with one O(4)SrCa3MnAl octahedra. The corner-sharing octahedral tilt angles range from 3-66°. In the sixth O site, O(6) is bonded to one Ca(2), one Ca(3), one Ca(4), one Ca(5), one Mn(1), and one Al(1) atom to form distorted OCa4MnAl octahedra that share corners with two equivalent O(6)Ca4MnAl octahedra, corners with two equivalent O(3)SrCa3Mn2 octahedra, corners with two equivalent O(5)SrCa3Mn2 octahedra, corners with four equivalent O(4)SrCa3MnAl octahedra, corners with six equivalent O(7)Ca4Mn2 octahedra, edges with two equivalent O(7)Ca4Mn2 octahedra, edges with two equivalent O(6)Ca4MnAl octahedra,  a faceface with one O(7)Ca4Mn2 octahedra,  a faceface with one O(6)Ca4MnAl octahedra,  a faceface with one O(5)SrCa3Mn2 octahedra, and  a faceface with one O(4)SrCa3MnAl octahedra. The corner-sharing octahedral tilt angles range from 1-70°. In the seventh O site, O(7) is bonded to one Ca(2), one Ca(3), one Ca(4), one Ca(5), one Mn(1), and one Mn(2) atom to form distorted OCa4Mn2 octahedra that share corners with two equivalent O(7)Ca4Mn2 octahedra, corners with two equivalent O(4)SrCa3MnAl octahedra, corners with four equivalent O(5)SrCa3Mn2 octahedra, corners with six equivalent O(6)Ca4MnAl octahedra, edges with two equivalent O(7)Ca4Mn2 octahedra, edges with two equivalent O(6)Ca4MnAl octahedra,  a faceface with one O(7)Ca4Mn2 octahedra,  a faceface with one O(6)Ca4MnAl octahedra,  a faceface with one O(3)SrCa3Mn2 octahedra,  a faceface with one O(5)SrCa3Mn2 octahedra, and  a faceface with one O(4)SrCa3MnAl octahedra. The corner-sharing octahedral tilt angles range from 3-65°.