SrCa7Mn8O21 crystallizes in the triclinic P1 space group. Sr(1) is bonded in a 9-coordinate geometry to one O(10), one O(14), one O(15), one O(18), one O(2), one O(4), one O(7), one O(8), and one O(9) atom. There are seven inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one O(10), one O(18), one O(19), one O(8), and one O(9) atom. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(10), one O(16), one O(17), one O(2), one O(20), one O(21), one O(7), and one O(9) atom. In the third Ca site, Ca(3) is bonded in a 7-coordinate geometry to one O(10), one O(17), one O(21), one O(5), one O(6), one O(8), and one O(9) atom. In the fourth Ca site, Ca(4) is bonded in a 8-coordinate geometry to one O(11), one O(12), one O(13), one O(14), one O(15), one O(19), one O(2), and one O(4) atom. In the fifth Ca site, Ca(5) is bonded in a 5-coordinate geometry to one O(1), one O(12), one O(13), one O(15), one O(18), one O(19), and one O(3) atom. In the sixth Ca site, Ca(6) is bonded in a 6-coordinate geometry to one O(11), one O(12), one O(13), one O(16), one O(2), one O(20), and one O(21) atom. In the seventh Ca site, Ca(7) is bonded in a 9-coordinate geometry to one O(1), one O(11), one O(13), one O(16), one O(17), one O(20), one O(3), one O(5), and one O(6) atom. There are eight inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(14), one O(16), and one O(7) atom to form distorted MnO4 trigonal pyramids that share corners with two equivalent Mn(3)O6 octahedra,  a cornercorner with one Mn(5)O5 square pyramid, and  a cornercorner with one Mn(2)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 20-25°. In the second Mn site, Mn(2) is bonded to one O(1), one O(11), one O(15), one O(17), and one O(8) atom to form MnO5 trigonal bipyramids that share corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mn(6)O6 octahedra, and  a cornercorner with one Mn(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 17-31°. In the third Mn site, Mn(3) is bonded to one O(12), one O(14), one O(16), one O(2), one O(3), and one O(9) atom to form MnO6 octahedra that share corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mn(7)O5 trigonal bipyramids, and corners with two equivalent Mn(1)O4 trigonal pyramids. The corner-sharing octahedral tilt angles range from 18-19°. In the fourth Mn site, Mn(4) is bonded to one O(10), one O(13), one O(15), one O(17), one O(2), and one O(3) atom to form MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(8)O5 square pyramids, and corners with two equivalent Mn(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 18-19°. In the fifth Mn site, Mn(5) is bonded to one O(18), one O(20), one O(4), one O(5), and one O(7) atom to form MnO5 square pyramids that share corners with two equivalent Mn(6)O6 octahedra, corners with two equivalent Mn(7)O5 trigonal bipyramids, and  a cornercorner with one Mn(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 24-32°. In the sixth Mn site, Mn(6) is bonded to one O(11), one O(19), one O(21), one O(4), one O(5), and one O(8) atom to form corner-sharing MnO6 octahedra. In the seventh Mn site, Mn(7) is bonded to one O(12), one O(18), one O(20), one O(6), and one O(9) atom to form MnO5 trigonal bipyramids that share corners with two equivalent Mn(3)O6 octahedra,  a cornercorner with one Mn(8)O5 square pyramid, and corners with two equivalent Mn(5)O5 square pyramids. The corner-sharing octahedral tilt angles range from 12-37°. In the eighth Mn site, Mn(8) is bonded to one O(10), one O(13), one O(19), one O(21), and one O(6) atom to form MnO5 square pyramids that share corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mn(6)O6 octahedra, and  a cornercorner with one Mn(7)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 15-35°. There are twenty-one inequivalent O sites. In the first O site, O(1) is bonded to one Ca(5), one Ca(7), one Mn(1), and one Mn(2) atom to form distorted OCa2Mn2 tetrahedra that share  a cornercorner with one O(7)SrCaMn2 tetrahedra and  a cornercorner with one O(19)Ca3Mn2 trigonal bipyramid. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Sr(1), one Ca(2), one Ca(4), one Ca(6), one Mn(3), and one Mn(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(5), one Ca(7), one Mn(3), and one Mn(4) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sr(1), one Ca(4), one Mn(5), and one Mn(6) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ca(3), one Ca(7), one Mn(5), and one Mn(6) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(3), one Ca(7), one Mn(7), and one Mn(8) atom. In the seventh O site, O(7) is bonded to one Sr(1), one Ca(2), one Mn(1), and one Mn(5) atom to form distorted OSrCaMn2 tetrahedra that share  a cornercorner with one O(1)Ca2Mn2 tetrahedra and  a cornercorner with one O(21)Ca3Mn2 trigonal bipyramid. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Sr(1), one Ca(1), one Ca(3), one Mn(2), and one Mn(6) atom. In the ninth O site, O(9) is bonded in a 6-coordinate geometry to one Sr(1), one Ca(1), one Ca(2), one Ca(3), one Mn(3), and one Mn(7) atom. In the tenth O site, O(10) is bonded in a 5-coordinate geometry to one Sr(1), one Ca(1), one Ca(2), one Ca(3), one Mn(4), and one Mn(8) atom. In the eleventh O site, O(11) is bonded in a 5-coordinate geometry to one Ca(4), one Ca(6), one Ca(7), one Mn(2), and one Mn(6) atom. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Ca(4), one Ca(5), one Ca(6), one Mn(3), and one Mn(7) atom. In the thirteenth O site, O(13) is bonded in a 6-coordinate geometry to one Ca(4), one Ca(5), one Ca(6), one Ca(7), one Mn(4), and one Mn(8) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one Sr(1), one Ca(4), one Mn(1), and one Mn(3) atom. In the fifteenth O site, O(15) is bonded in a 5-coordinate geometry to one Sr(1), one Ca(4), one Ca(5), one Mn(2), and one Mn(4) atom. In the sixteenth O site, O(16) is bonded in a 5-coordinate geometry to one Ca(2), one Ca(6), one Ca(7), one Mn(1), and one Mn(3) atom. In the seventeenth O site, O(17) is bonded in a 5-coordinate geometry to one Ca(2), one Ca(3), one Ca(7), one Mn(2), and one Mn(4) atom. In the eighteenth O site, O(18) is bonded in a 5-coordinate geometry to one Sr(1), one Ca(1), one Ca(5), one Mn(5), and one Mn(7) atom. In the nineteenth O site, O(19) is bonded to one Ca(1), one Ca(4), one Ca(5), one Mn(6), and one Mn(8) atom to form distorted OCa3Mn2 trigonal bipyramids that share  a cornercorner with one O(1)Ca2Mn2 tetrahedra and corners with two equivalent O(21)Ca3Mn2 trigonal bipyramids. In the twentieth O site, O(20) is bonded in a 5-coordinate geometry to one Ca(2), one Ca(6), one Ca(7), one Mn(5), and one Mn(7) atom. In the twenty-first O site, O(21) is bonded to one Ca(2), one Ca(3), one Ca(6), one Mn(6), and one Mn(8) atom to form distorted OCa3Mn2 trigonal bipyramids that share  a cornercorner with one O(7)SrCaMn2 tetrahedra and corners with two equivalent O(19)Ca3Mn2 trigonal bipyramids.
SrCa7Mn8O21 crystallizes in the triclinic P1 space group. Sr(1) is bonded in a 9-coordinate geometry to one O(10), one O(14), one O(15), one O(18), one O(2), one O(4), one O(7), one O(8), and one O(9) atom. The Sr(1)-O(10) bond length is 2.71 Å. The Sr(1)-O(14) bond length is 2.61 Å. The Sr(1)-O(15) bond length is 2.76 Å. The Sr(1)-O(18) bond length is 2.91 Å. The Sr(1)-O(2) bond length is 2.59 Å. The Sr(1)-O(4) bond length is 2.68 Å. The Sr(1)-O(7) bond length is 2.52 Å. The Sr(1)-O(8) bond length is 2.66 Å. The Sr(1)-O(9) bond length is 2.96 Å. There are seven inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one O(10), one O(18), one O(19), one O(8), and one O(9) atom. The Ca(1)-O(10) bond length is 2.31 Å. The Ca(1)-O(18) bond length is 2.34 Å. The Ca(1)-O(19) bond length is 2.54 Å. The Ca(1)-O(8) bond length is 2.39 Å. The Ca(1)-O(9) bond length is 2.77 Å. In the second Ca site, Ca(2) is bonded in a 8-coordinate geometry to one O(10), one O(16), one O(17), one O(2), one O(20), one O(21), one O(7), and one O(9) atom. The Ca(2)-O(10) bond length is 2.97 Å. The Ca(2)-O(16) bond length is 2.87 Å. The Ca(2)-O(17) bond length is 2.55 Å. The Ca(2)-O(2) bond length is 2.35 Å. The Ca(2)-O(20) bond length is 2.64 Å. The Ca(2)-O(21) bond length is 2.41 Å. The Ca(2)-O(7) bond length is 2.28 Å. The Ca(2)-O(9) bond length is 2.52 Å. In the third Ca site, Ca(3) is bonded in a 7-coordinate geometry to one O(10), one O(17), one O(21), one O(5), one O(6), one O(8), and one O(9) atom. The Ca(3)-O(10) bond length is 2.54 Å. The Ca(3)-O(17) bond length is 2.40 Å. The Ca(3)-O(21) bond length is 2.53 Å. The Ca(3)-O(5) bond length is 2.41 Å. The Ca(3)-O(6) bond length is 2.45 Å. The Ca(3)-O(8) bond length is 2.72 Å. The Ca(3)-O(9) bond length is 2.66 Å. In the fourth Ca site, Ca(4) is bonded in a 8-coordinate geometry to one O(11), one O(12), one O(13), one O(14), one O(15), one O(19), one O(2), and one O(4) atom. The Ca(4)-O(11) bond length is 2.57 Å. The Ca(4)-O(12) bond length is 2.34 Å. The Ca(4)-O(13) bond length is 2.58 Å. The Ca(4)-O(14) bond length is 2.48 Å. The Ca(4)-O(15) bond length is 2.34 Å. The Ca(4)-O(19) bond length is 2.49 Å. The Ca(4)-O(2) bond length is 2.84 Å. The Ca(4)-O(4) bond length is 2.41 Å. In the fifth Ca site, Ca(5) is bonded in a 5-coordinate geometry to one O(1), one O(12), one O(13), one O(15), one O(18), one O(19), and one O(3) atom. The Ca(5)-O(1) bond length is 2.30 Å. The Ca(5)-O(12) bond length is 2.91 Å. The Ca(5)-O(13) bond length is 2.95 Å. The Ca(5)-O(15) bond length is 2.54 Å. The Ca(5)-O(18) bond length is 2.48 Å. The Ca(5)-O(19) bond length is 2.42 Å. The Ca(5)-O(3) bond length is 2.38 Å. In the sixth Ca site, Ca(6) is bonded in a 6-coordinate geometry to one O(11), one O(12), one O(13), one O(16), one O(2), one O(20), and one O(21) atom. The Ca(6)-O(11) bond length is 2.34 Å. The Ca(6)-O(12) bond length is 2.47 Å. The Ca(6)-O(13) bond length is 2.33 Å. The Ca(6)-O(16) bond length is 2.33 Å. The Ca(6)-O(2) bond length is 2.92 Å. The Ca(6)-O(20) bond length is 2.34 Å. The Ca(6)-O(21) bond length is 2.47 Å. In the seventh Ca site, Ca(7) is bonded in a 9-coordinate geometry to one O(1), one O(11), one O(13), one O(16), one O(17), one O(20), one O(3), one O(5), and one O(6) atom. The Ca(7)-O(1) bond length is 2.30 Å. The Ca(7)-O(11) bond length is 2.85 Å. The Ca(7)-O(13) bond length is 2.68 Å. The Ca(7)-O(16) bond length is 2.66 Å. The Ca(7)-O(17) bond length is 2.77 Å. The Ca(7)-O(20) bond length is 2.81 Å. The Ca(7)-O(3) bond length is 2.49 Å. The Ca(7)-O(5) bond length is 2.49 Å. The Ca(7)-O(6) bond length is 2.37 Å. There are eight inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(14), one O(16), and one O(7) atom to form distorted MnO4 trigonal pyramids that share corners with two equivalent Mn(3)O6 octahedra,  a cornercorner with one Mn(5)O5 square pyramid, and  a cornercorner with one Mn(2)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 20-25°. The Mn(1)-O(1) bond length is 1.88 Å. The Mn(1)-O(14) bond length is 1.90 Å. The Mn(1)-O(16) bond length is 1.91 Å. The Mn(1)-O(7) bond length is 1.89 Å. In the second Mn site, Mn(2) is bonded to one O(1), one O(11), one O(15), one O(17), and one O(8) atom to form MnO5 trigonal bipyramids that share corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mn(6)O6 octahedra, and  a cornercorner with one Mn(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 17-31°. The Mn(2)-O(1) bond length is 2.06 Å. The Mn(2)-O(11) bond length is 1.94 Å. The Mn(2)-O(15) bond length is 1.95 Å. The Mn(2)-O(17) bond length is 1.94 Å. The Mn(2)-O(8) bond length is 1.98 Å. In the third Mn site, Mn(3) is bonded to one O(12), one O(14), one O(16), one O(2), one O(3), and one O(9) atom to form MnO6 octahedra that share corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mn(7)O5 trigonal bipyramids, and corners with two equivalent Mn(1)O4 trigonal pyramids. The corner-sharing octahedral tilt angles range from 18-19°. The Mn(3)-O(12) bond length is 2.14 Å. The Mn(3)-O(14) bond length is 2.05 Å. The Mn(3)-O(16) bond length is 2.04 Å. The Mn(3)-O(2) bond length is 1.94 Å. The Mn(3)-O(3) bond length is 1.95 Å. The Mn(3)-O(9) bond length is 2.09 Å. In the fourth Mn site, Mn(4) is bonded to one O(10), one O(13), one O(15), one O(17), one O(2), and one O(3) atom to form MnO6 octahedra that share corners with two equivalent Mn(3)O6 octahedra, corners with two equivalent Mn(8)O5 square pyramids, and corners with two equivalent Mn(2)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 18-19°. The Mn(4)-O(10) bond length is 2.04 Å. The Mn(4)-O(13) bond length is 1.99 Å. The Mn(4)-O(15) bond length is 1.98 Å. The Mn(4)-O(17) bond length is 1.96 Å. The Mn(4)-O(2) bond length is 1.91 Å. The Mn(4)-O(3) bond length is 1.98 Å. In the fifth Mn site, Mn(5) is bonded to one O(18), one O(20), one O(4), one O(5), and one O(7) atom to form MnO5 square pyramids that share corners with two equivalent Mn(6)O6 octahedra, corners with two equivalent Mn(7)O5 trigonal bipyramids, and  a cornercorner with one Mn(1)O4 trigonal pyramid. The corner-sharing octahedral tilt angles range from 24-32°. The Mn(5)-O(18) bond length is 1.98 Å. The Mn(5)-O(20) bond length is 1.97 Å. The Mn(5)-O(4) bond length is 1.95 Å. The Mn(5)-O(5) bond length is 1.98 Å. The Mn(5)-O(7) bond length is 2.05 Å. In the sixth Mn site, Mn(6) is bonded to one O(11), one O(19), one O(21), one O(4), one O(5), and one O(8) atom to form corner-sharing MnO6 octahedra. The Mn(6)-O(11) bond length is 2.04 Å. The Mn(6)-O(19) bond length is 2.02 Å. The Mn(6)-O(21) bond length is 2.05 Å. The Mn(6)-O(4) bond length is 1.98 Å. The Mn(6)-O(5) bond length is 2.00 Å. The Mn(6)-O(8) bond length is 2.07 Å. In the seventh Mn site, Mn(7) is bonded to one O(12), one O(18), one O(20), one O(6), and one O(9) atom to form MnO5 trigonal bipyramids that share corners with two equivalent Mn(3)O6 octahedra,  a cornercorner with one Mn(8)O5 square pyramid, and corners with two equivalent Mn(5)O5 square pyramids. The corner-sharing octahedral tilt angles range from 12-37°. The Mn(7)-O(12) bond length is 1.89 Å. The Mn(7)-O(18) bond length is 2.01 Å. The Mn(7)-O(20) bond length is 1.96 Å. The Mn(7)-O(6) bond length is 1.89 Å. The Mn(7)-O(9) bond length is 1.92 Å. In the eighth Mn site, Mn(8) is bonded to one O(10), one O(13), one O(19), one O(21), and one O(6) atom to form MnO5 square pyramids that share corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mn(6)O6 octahedra, and  a cornercorner with one Mn(7)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 15-35°. The Mn(8)-O(10) bond length is 1.97 Å. The Mn(8)-O(13) bond length is 1.91 Å. The Mn(8)-O(19) bond length is 1.95 Å. The Mn(8)-O(21) bond length is 1.95 Å. The Mn(8)-O(6) bond length is 1.91 Å. There are twenty-one inequivalent O sites. In the first O site, O(1) is bonded to one Ca(5), one Ca(7), one Mn(1), and one Mn(2) atom to form distorted OCa2Mn2 tetrahedra that share  a cornercorner with one O(7)SrCaMn2 tetrahedra and  a cornercorner with one O(19)Ca3Mn2 trigonal bipyramid. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Sr(1), one Ca(2), one Ca(4), one Ca(6), one Mn(3), and one Mn(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Ca(5), one Ca(7), one Mn(3), and one Mn(4) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sr(1), one Ca(4), one Mn(5), and one Mn(6) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Ca(3), one Ca(7), one Mn(5), and one Mn(6) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Ca(3), one Ca(7), one Mn(7), and one Mn(8) atom. In the seventh O site, O(7) is bonded to one Sr(1), one Ca(2), one Mn(1), and one Mn(5) atom to form distorted OSrCaMn2 tetrahedra that share  a cornercorner with one O(1)Ca2Mn2 tetrahedra and  a cornercorner with one O(21)Ca3Mn2 trigonal bipyramid. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Sr(1), one Ca(1), one Ca(3), one Mn(2), and one Mn(6) atom. In the ninth O site, O(9) is bonded in a 6-coordinate geometry to one Sr(1), one Ca(1), one Ca(2), one Ca(3), one Mn(3), and one Mn(7) atom. In the tenth O site, O(10) is bonded in a 5-coordinate geometry to one Sr(1), one Ca(1), one Ca(2), one Ca(3), one Mn(4), and one Mn(8) atom. In the eleventh O site, O(11) is bonded in a 5-coordinate geometry to one Ca(4), one Ca(6), one Ca(7), one Mn(2), and one Mn(6) atom. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Ca(4), one Ca(5), one Ca(6), one Mn(3), and one Mn(7) atom. In the thirteenth O site, O(13) is bonded in a 6-coordinate geometry to one Ca(4), one Ca(5), one Ca(6), one Ca(7), one Mn(4), and one Mn(8) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one Sr(1), one Ca(4), one Mn(1), and one Mn(3) atom. In the fifteenth O site, O(15) is bonded in a 5-coordinate geometry to one Sr(1), one Ca(4), one Ca(5), one Mn(2), and one Mn(4) atom. In the sixteenth O site, O(16) is bonded in a 5-coordinate geometry to one Ca(2), one Ca(6), one Ca(7), one Mn(1), and one Mn(3) atom. In the seventeenth O site, O(17) is bonded in a 5-coordinate geometry to one Ca(2), one Ca(3), one Ca(7), one Mn(2), and one Mn(4) atom. In the eighteenth O site, O(18) is bonded in a 5-coordinate geometry to one Sr(1), one Ca(1), one Ca(5), one Mn(5), and one Mn(7) atom. In the nineteenth O site, O(19) is bonded to one Ca(1), one Ca(4), one Ca(5), one Mn(6), and one Mn(8) atom to form distorted OCa3Mn2 trigonal bipyramids that share  a cornercorner with one O(1)Ca2Mn2 tetrahedra and corners with two equivalent O(21)Ca3Mn2 trigonal bipyramids. In the twentieth O site, O(20) is bonded in a 5-coordinate geometry to one Ca(2), one Ca(6), one Ca(7), one Mn(5), and one Mn(7) atom. In the twenty-first O site, O(21) is bonded to one Ca(2), one Ca(3), one Ca(6), one Mn(6), and one Mn(8) atom to form distorted OCa3Mn2 trigonal bipyramids that share  a cornercorner with one O(7)SrCaMn2 tetrahedra and corners with two equivalent O(19)Ca3Mn2 trigonal bipyramids.