Ba5Tm8Zn4O21 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 10-coordinate geometry to two equivalent O(2), four equivalent O(1), and four equivalent O(3) atoms. In the second Ba site, Ba(2) is bonded in a distorted q6 geometry to two equivalent O(4) and eight equivalent O(2) atoms. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(4), two equivalent O(1), and four equivalent O(2) atoms to form distorted TmO7 pentagonal bipyramids that share  a cornercorner with one Tm(1)O7 pentagonal bipyramid, corners with two equivalent Zn(1)O5 trigonal bipyramids, edges with two equivalent Zn(1)O5 trigonal bipyramids, and faces with two equivalent Tm(1)O7 pentagonal bipyramids. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(3), two equivalent O(2), and four equivalent O(1) atoms. Zn(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form distorted ZnO5 trigonal bipyramids that share corners with two equivalent Tm(1)O7 pentagonal bipyramids and edges with two equivalent Tm(1)O7 pentagonal bipyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Tm(1), two equivalent Tm(2), and one Zn(1) atom. In the second O site, O(2) is bonded to one Ba(1), one Ba(2), one Tm(2), two equivalent Tm(1), and one Zn(1) atom to form distorted OBa2Tm3Zn octahedra that share  a cornercorner with one O(4)Ba2Tm4 octahedra, corners with three equivalent O(3)Ba4TmZn octahedra, corners with six equivalent O(2)Ba2Tm3Zn octahedra, edges with two equivalent O(2)Ba2Tm3Zn octahedra,  a faceface with one O(4)Ba2Tm4 octahedra,  a faceface with one O(3)Ba4TmZn octahedra, and faces with two equivalent O(2)Ba2Tm3Zn octahedra. The corner-sharing octahedral tilt angles range from 0-76°. In the third O site, O(3) is bonded to four equivalent Ba(1), one Tm(2), and one Zn(1) atom to form distorted OBa4TmZn octahedra that share corners with two equivalent O(3)Ba4TmZn octahedra, corners with six equivalent O(2)Ba2Tm3Zn octahedra, edges with five equivalent O(3)Ba4TmZn octahedra, and faces with two equivalent O(2)Ba2Tm3Zn octahedra. The corner-sharing octahedral tilt angles range from 6-60°. In the fourth O site, O(4) is bonded to two equivalent Ba(2) and four equivalent Tm(1) atoms to form OBa2Tm4 octahedra that share corners with two equivalent O(4)Ba2Tm4 octahedra, corners with eight equivalent O(2)Ba2Tm3Zn octahedra, and faces with eight equivalent O(2)Ba2Tm3Zn octahedra. The corner-sharing octahedral tilt angles range from 0-60°.
Ba5Tm8Zn4O21 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 10-coordinate geometry to two equivalent O(2), four equivalent O(1), and four equivalent O(3) atoms. Both Ba(1)-O(2) bond lengths are 2.89 Å. There are two shorter (3.20 Å) and two longer (3.25 Å) Ba(1)-O(1) bond lengths. There are a spread of Ba(1)-O(3) bond distances ranging from 2.66-2.86 Å. In the second Ba site, Ba(2) is bonded in a distorted q6 geometry to two equivalent O(4) and eight equivalent O(2) atoms. Both Ba(2)-O(4) bond lengths are 2.85 Å. All Ba(2)-O(2) bond lengths are 2.91 Å. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(4), two equivalent O(1), and four equivalent O(2) atoms to form distorted TmO7 pentagonal bipyramids that share  a cornercorner with one Tm(1)O7 pentagonal bipyramid, corners with two equivalent Zn(1)O5 trigonal bipyramids, edges with two equivalent Zn(1)O5 trigonal bipyramids, and faces with two equivalent Tm(1)O7 pentagonal bipyramids. The Tm(1)-O(4) bond length is 2.30 Å. Both Tm(1)-O(1) bond lengths are 2.28 Å. There are two shorter (2.26 Å) and two longer (2.41 Å) Tm(1)-O(2) bond lengths. In the second Tm site, Tm(2) is bonded in a 7-coordinate geometry to one O(3), two equivalent O(2), and four equivalent O(1) atoms. The Tm(2)-O(3) bond length is 2.45 Å. Both Tm(2)-O(2) bond lengths are 2.39 Å. There are two shorter (2.27 Å) and two longer (2.31 Å) Tm(2)-O(1) bond lengths. Zn(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form distorted ZnO5 trigonal bipyramids that share corners with two equivalent Tm(1)O7 pentagonal bipyramids and edges with two equivalent Tm(1)O7 pentagonal bipyramids. The Zn(1)-O(3) bond length is 2.00 Å. Both Zn(1)-O(1) bond lengths are 2.07 Å. Both Zn(1)-O(2) bond lengths are 2.13 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Tm(1), two equivalent Tm(2), and one Zn(1) atom. In the second O site, O(2) is bonded to one Ba(1), one Ba(2), one Tm(2), two equivalent Tm(1), and one Zn(1) atom to form distorted OBa2Tm3Zn octahedra that share  a cornercorner with one O(4)Ba2Tm4 octahedra, corners with three equivalent O(3)Ba4TmZn octahedra, corners with six equivalent O(2)Ba2Tm3Zn octahedra, edges with two equivalent O(2)Ba2Tm3Zn octahedra,  a faceface with one O(4)Ba2Tm4 octahedra,  a faceface with one O(3)Ba4TmZn octahedra, and faces with two equivalent O(2)Ba2Tm3Zn octahedra. The corner-sharing octahedral tilt angles range from 0-76°. In the third O site, O(3) is bonded to four equivalent Ba(1), one Tm(2), and one Zn(1) atom to form distorted OBa4TmZn octahedra that share corners with two equivalent O(3)Ba4TmZn octahedra, corners with six equivalent O(2)Ba2Tm3Zn octahedra, edges with five equivalent O(3)Ba4TmZn octahedra, and faces with two equivalent O(2)Ba2Tm3Zn octahedra. The corner-sharing octahedral tilt angles range from 6-60°. In the fourth O site, O(4) is bonded to two equivalent Ba(2) and four equivalent Tm(1) atoms to form OBa2Tm4 octahedra that share corners with two equivalent O(4)Ba2Tm4 octahedra, corners with eight equivalent O(2)Ba2Tm3Zn octahedra, and faces with eight equivalent O(2)Ba2Tm3Zn octahedra. The corner-sharing octahedral tilt angles range from 0-60°.