Ba5Y8Mn4O21 crystallizes in the tetragonal I4/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a distorted q6 geometry to two equivalent O(1) and eight equivalent O(3) atoms. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to two equivalent O(3), four equivalent O(2), and four equivalent O(4) atoms. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(3), and four equivalent O(4) atoms. In the second Y site, Y(2) is bonded to one O(1), two equivalent O(4), and four equivalent O(3) atoms to form distorted YO7 pentagonal bipyramids that share  a cornercorner with one Y(2)O7 pentagonal bipyramid, corners with two equivalent Mn(1)O5 trigonal bipyramids, edges with two equivalent Mn(1)O5 trigonal bipyramids, and faces with two equivalent Y(2)O7 pentagonal bipyramids. Mn(1) is bonded to one O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Y(2)O7 pentagonal bipyramids and edges with two equivalent Y(2)O7 pentagonal bipyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1) and four equivalent Y(2) atoms to form OBa2Y4 octahedra that share corners with two equivalent O(1)Ba2Y4 octahedra, corners with eight equivalent O(3)Ba2Y3Mn octahedra, and faces with eight equivalent O(3)Ba2Y3Mn octahedra. The corner-sharing octahedral tilt angles range from 0-61°. In the second O site, O(2) is bonded to four equivalent Ba(2), one Y(1), and one Mn(1) atom to form distorted OBa4YMn octahedra that share corners with two equivalent O(2)Ba4YMn octahedra, corners with six equivalent O(3)Ba2Y3Mn octahedra, edges with five equivalent O(2)Ba4YMn octahedra, and faces with two equivalent O(3)Ba2Y3Mn octahedra. The corner-sharing octahedral tilt angles range from 7-59°. In the third O site, O(3) is bonded to one Ba(1), one Ba(2), one Y(1), two equivalent Y(2), and one Mn(1) atom to form distorted OBa2Y3Mn octahedra that share  a cornercorner with one O(1)Ba2Y4 octahedra, corners with three equivalent O(2)Ba4YMn octahedra, corners with six equivalent O(3)Ba2Y3Mn octahedra, edges with two equivalent O(3)Ba2Y3Mn octahedra,  a faceface with one O(1)Ba2Y4 octahedra,  a faceface with one O(2)Ba4YMn octahedra, and faces with two equivalent O(3)Ba2Y3Mn octahedra. The corner-sharing octahedral tilt angles range from 0-76°. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ba(2), one Y(2), two equivalent Y(1), and one Mn(1) atom.
Ba5Y8Mn4O21 crystallizes in the tetragonal I4/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a distorted q6 geometry to two equivalent O(1) and eight equivalent O(3) atoms. Both Ba(1)-O(1) bond lengths are 2.91 Å. All Ba(1)-O(3) bond lengths are 2.96 Å. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to two equivalent O(3), four equivalent O(2), and four equivalent O(4) atoms. Both Ba(2)-O(3) bond lengths are 2.96 Å. There are a spread of Ba(2)-O(2) bond distances ranging from 2.67-2.91 Å. All Ba(2)-O(4) bond lengths are 3.30 Å. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(3), and four equivalent O(4) atoms. The Y(1)-O(2) bond length is 2.54 Å. Both Y(1)-O(3) bond lengths are 2.46 Å. There are two shorter (2.29 Å) and two longer (2.35 Å) Y(1)-O(4) bond lengths. In the second Y site, Y(2) is bonded to one O(1), two equivalent O(4), and four equivalent O(3) atoms to form distorted YO7 pentagonal bipyramids that share  a cornercorner with one Y(2)O7 pentagonal bipyramid, corners with two equivalent Mn(1)O5 trigonal bipyramids, edges with two equivalent Mn(1)O5 trigonal bipyramids, and faces with two equivalent Y(2)O7 pentagonal bipyramids. The Y(2)-O(1) bond length is 2.34 Å. Both Y(2)-O(4) bond lengths are 2.33 Å. There are two shorter (2.30 Å) and two longer (2.47 Å) Y(2)-O(3) bond lengths. Mn(1) is bonded to one O(2), two equivalent O(3), and two equivalent O(4) atoms to form distorted MnO5 trigonal bipyramids that share corners with two equivalent Y(2)O7 pentagonal bipyramids and edges with two equivalent Y(2)O7 pentagonal bipyramids. The Mn(1)-O(2) bond length is 2.07 Å. Both Mn(1)-O(3) bond lengths are 2.16 Å. Both Mn(1)-O(4) bond lengths are 2.12 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1) and four equivalent Y(2) atoms to form OBa2Y4 octahedra that share corners with two equivalent O(1)Ba2Y4 octahedra, corners with eight equivalent O(3)Ba2Y3Mn octahedra, and faces with eight equivalent O(3)Ba2Y3Mn octahedra. The corner-sharing octahedral tilt angles range from 0-61°. In the second O site, O(2) is bonded to four equivalent Ba(2), one Y(1), and one Mn(1) atom to form distorted OBa4YMn octahedra that share corners with two equivalent O(2)Ba4YMn octahedra, corners with six equivalent O(3)Ba2Y3Mn octahedra, edges with five equivalent O(2)Ba4YMn octahedra, and faces with two equivalent O(3)Ba2Y3Mn octahedra. The corner-sharing octahedral tilt angles range from 7-59°. In the third O site, O(3) is bonded to one Ba(1), one Ba(2), one Y(1), two equivalent Y(2), and one Mn(1) atom to form distorted OBa2Y3Mn octahedra that share  a cornercorner with one O(1)Ba2Y4 octahedra, corners with three equivalent O(2)Ba4YMn octahedra, corners with six equivalent O(3)Ba2Y3Mn octahedra, edges with two equivalent O(3)Ba2Y3Mn octahedra,  a faceface with one O(1)Ba2Y4 octahedra,  a faceface with one O(2)Ba4YMn octahedra, and faces with two equivalent O(3)Ba2Y3Mn octahedra. The corner-sharing octahedral tilt angles range from 0-76°. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ba(2), one Y(2), two equivalent Y(1), and one Mn(1) atom.