Ba3Fe8Sn3O20 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to one O(2), one O(3), two equivalent O(5), two equivalent O(6), and four equivalent O(4) atoms. In the second Ba site, Ba(2) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(5) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form FeO4 tetrahedra that share  a cornercorner with one Sn(1)O6 octahedra, corners with two equivalent Sn(2)O6 octahedra, and corners with three equivalent Fe(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-64°. In the second Fe site, Fe(2) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form FeO4 tetrahedra that share  a cornercorner with one Sn(2)O6 octahedra,  a cornercorner with one Fe(2)O4 tetrahedra, and corners with three equivalent Fe(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to two equivalent O(2) and four equivalent O(6) atoms to form SnO6 octahedra that share corners with four equivalent Fe(1)O4 tetrahedra and edges with four equivalent Sn(2)O6 octahedra. In the second Sn site, Sn(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form SnO6 octahedra that share corners with two equivalent Fe(2)O4 tetrahedra, corners with four equivalent Fe(1)O4 tetrahedra,  an edgeedge with one Sn(2)O6 octahedra, and edges with two equivalent Sn(1)O6 octahedra. There are six inequivalent O sites. In the first O site, O(2) is bonded to one Ba(1), one Sn(1), and two equivalent Sn(2) atoms to form distorted OBaSn3 tetrahedra that share  a cornercorner with one O(2)BaSn3 tetrahedra, corners with two equivalent O(5)Ba2Fe2 tetrahedra, and  an edgeedge with one O(2)BaSn3 tetrahedra. In the second O site, O(3) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ba(2), and two equivalent Fe(2) atoms. In the third O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Fe(1), and one Fe(2) atom. In the fourth O site, O(5) is bonded to one Ba(1), one Ba(2), one Fe(1), and one Fe(2) atom to form distorted OBa2Fe2 tetrahedra that share  a cornercorner with one O(2)BaSn3 tetrahedra, corners with two equivalent O(5)Ba2Fe2 tetrahedra, and  an edgeedge with one O(5)Ba2Fe2 tetrahedra. In the fifth O site, O(6) is bonded in a 3-coordinate geometry to one Ba(1), one Fe(1), one Sn(1), and one Sn(2) atom. In the sixth O site, O(1) is bonded in a trigonal planar geometry to one Fe(1), one Fe(2), and one Sn(2) atom.
Ba3Fe8Sn3O20 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to one O(2), one O(3), two equivalent O(5), two equivalent O(6), and four equivalent O(4) atoms. The Ba(1)-O(2) bond length is 2.77 Å. The Ba(1)-O(3) bond length is 3.41 Å. Both Ba(1)-O(5) bond lengths are 2.76 Å. Both Ba(1)-O(6) bond lengths are 3.20 Å. There are two shorter (2.88 Å) and two longer (3.46 Å) Ba(1)-O(4) bond lengths. In the second Ba site, Ba(2) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(5) atoms. Both Ba(2)-O(3) bond lengths are 2.78 Å. All Ba(2)-O(5) bond lengths are 2.91 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form FeO4 tetrahedra that share  a cornercorner with one Sn(1)O6 octahedra, corners with two equivalent Sn(2)O6 octahedra, and corners with three equivalent Fe(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 46-64°. The Fe(1)-O(1) bond length is 1.94 Å. The Fe(1)-O(4) bond length is 1.80 Å. The Fe(1)-O(5) bond length is 1.84 Å. The Fe(1)-O(6) bond length is 1.99 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(3), one O(4), and one O(5) atom to form FeO4 tetrahedra that share  a cornercorner with one Sn(2)O6 octahedra,  a cornercorner with one Fe(2)O4 tetrahedra, and corners with three equivalent Fe(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. The Fe(2)-O(1) bond length is 1.97 Å. The Fe(2)-O(3) bond length is 1.87 Å. The Fe(2)-O(4) bond length is 1.87 Å. The Fe(2)-O(5) bond length is 1.94 Å. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to two equivalent O(2) and four equivalent O(6) atoms to form SnO6 octahedra that share corners with four equivalent Fe(1)O4 tetrahedra and edges with four equivalent Sn(2)O6 octahedra. Both Sn(1)-O(2) bond lengths are 2.08 Å. All Sn(1)-O(6) bond lengths are 2.10 Å. In the second Sn site, Sn(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(6) atoms to form SnO6 octahedra that share corners with two equivalent Fe(2)O4 tetrahedra, corners with four equivalent Fe(1)O4 tetrahedra,  an edgeedge with one Sn(2)O6 octahedra, and edges with two equivalent Sn(1)O6 octahedra. Both Sn(2)-O(1) bond lengths are 2.04 Å. Both Sn(2)-O(2) bond lengths are 2.21 Å. Both Sn(2)-O(6) bond lengths are 2.09 Å. There are six inequivalent O sites. In the first O site, O(2) is bonded to one Ba(1), one Sn(1), and two equivalent Sn(2) atoms to form distorted OBaSn3 tetrahedra that share  a cornercorner with one O(2)BaSn3 tetrahedra, corners with two equivalent O(5)Ba2Fe2 tetrahedra, and  an edgeedge with one O(2)BaSn3 tetrahedra. In the second O site, O(3) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ba(2), and two equivalent Fe(2) atoms. In the third O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Ba(1), one Fe(1), and one Fe(2) atom. In the fourth O site, O(5) is bonded to one Ba(1), one Ba(2), one Fe(1), and one Fe(2) atom to form distorted OBa2Fe2 tetrahedra that share  a cornercorner with one O(2)BaSn3 tetrahedra, corners with two equivalent O(5)Ba2Fe2 tetrahedra, and  an edgeedge with one O(5)Ba2Fe2 tetrahedra. In the fifth O site, O(6) is bonded in a 3-coordinate geometry to one Ba(1), one Fe(1), one Sn(1), and one Sn(2) atom. In the sixth O site, O(1) is bonded in a trigonal planar geometry to one Fe(1), one Fe(2), and one Sn(2) atom.