Ba3Eu3(Fe3O8)2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to one O(5), two equivalent O(2), two equivalent O(3), three equivalent O(4), and four equivalent O(1) atoms to form distorted BaO12 cuboctahedra that share  a cornercorner with one Ba(2)O12 cuboctahedra, corners with three equivalent Ba(1)O12 cuboctahedra, faces with two equivalent Ba(1)O12 cuboctahedra, faces with two equivalent Ba(2)O12 cuboctahedra, faces with three equivalent Fe(3)O6 octahedra, faces with two equivalent Fe(2)O5 square pyramids, and faces with three equivalent Fe(1)O5 square pyramids. In the second Ba site, Ba(2) is bonded to two equivalent O(4), two equivalent O(5), four equivalent O(2), and four equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with two equivalent Ba(1)O12 cuboctahedra, corners with two equivalent Ba(2)O12 cuboctahedra, faces with four equivalent Ba(1)O12 cuboctahedra, faces with two equivalent Fe(3)O6 octahedra, faces with two equivalent Fe(1)O5 square pyramids, and faces with four equivalent Fe(2)O5 square pyramids. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a distorted q6 geometry to two equivalent O(6), four equivalent O(1), and four equivalent O(3) atoms. In the second Eu site, Eu(2) is bonded in a distorted q6 geometry to one O(6), two equivalent O(1), two equivalent O(3), and four equivalent O(2) atoms. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(2) atoms to form distorted FeO5 square pyramids that share corners with three equivalent Fe(3)O6 octahedra, corners with two equivalent Fe(2)O5 square pyramids,  a faceface with one Ba(2)O12 cuboctahedra, and faces with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 1-14°. In the second Fe site, Fe(2) is bonded to one O(5), two equivalent O(2), and two equivalent O(3) atoms to form FeO5 square pyramids that share corners with two equivalent Fe(3)O6 octahedra,  a cornercorner with one Fe(2)O5 square pyramid, corners with two equivalent Fe(1)O5 square pyramids, faces with two equivalent Ba(1)O12 cuboctahedra, and faces with two equivalent Ba(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 14°. In the third Fe site, Fe(3) is bonded to one O(4), one O(6), two equivalent O(1), and two equivalent O(3) atoms to form FeO6 octahedra that share  a cornercorner with one Fe(3)O6 octahedra, corners with two equivalent Fe(2)O5 square pyramids, corners with three equivalent Fe(1)O5 square pyramids,  a faceface with one Ba(2)O12 cuboctahedra, and faces with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. There are six inequivalent O sites. In the first O site, O(4) is bonded to one Ba(2), three equivalent Ba(1), one Fe(1), and one Fe(3) atom to form a mixture of distorted corner and edge-sharing OBa4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. In the second O site, O(5) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Fe(2) atoms to form a mixture of distorted corner and edge-sharing OBa4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the third O site, O(6) is bonded in a distorted linear geometry to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Fe(3) atoms. In the fourth O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Ba(1), one Eu(1), one Eu(2), one Fe(1), and one Fe(3) atom. In the fifth O site, O(2) is bonded in a 6-coordinate geometry to one Ba(1), one Ba(2), two equivalent Eu(2), one Fe(1), and one Fe(2) atom. In the sixth O site, O(3) is bonded in a 6-coordinate geometry to one Ba(1), one Ba(2), one Eu(1), one Eu(2), one Fe(2), and one Fe(3) atom.
Ba3Eu3(Fe3O8)2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to one O(5), two equivalent O(2), two equivalent O(3), three equivalent O(4), and four equivalent O(1) atoms to form distorted BaO12 cuboctahedra that share  a cornercorner with one Ba(2)O12 cuboctahedra, corners with three equivalent Ba(1)O12 cuboctahedra, faces with two equivalent Ba(1)O12 cuboctahedra, faces with two equivalent Ba(2)O12 cuboctahedra, faces with three equivalent Fe(3)O6 octahedra, faces with two equivalent Fe(2)O5 square pyramids, and faces with three equivalent Fe(1)O5 square pyramids. The Ba(1)-O(5) bond length is 2.87 Å. Both Ba(1)-O(2) bond lengths are 3.16 Å. Both Ba(1)-O(3) bond lengths are 3.02 Å. There are two shorter (2.84 Å) and one longer (2.85 Å) Ba(1)-O(4) bond length. There are two shorter (2.98 Å) and two longer (3.02 Å) Ba(1)-O(1) bond lengths. In the second Ba site, Ba(2) is bonded to two equivalent O(4), two equivalent O(5), four equivalent O(2), and four equivalent O(3) atoms to form BaO12 cuboctahedra that share corners with two equivalent Ba(1)O12 cuboctahedra, corners with two equivalent Ba(2)O12 cuboctahedra, faces with four equivalent Ba(1)O12 cuboctahedra, faces with two equivalent Fe(3)O6 octahedra, faces with two equivalent Fe(1)O5 square pyramids, and faces with four equivalent Fe(2)O5 square pyramids. Both Ba(2)-O(4) bond lengths are 2.79 Å. Both Ba(2)-O(5) bond lengths are 2.84 Å. All Ba(2)-O(2) bond lengths are 3.12 Å. All Ba(2)-O(3) bond lengths are 3.02 Å. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a distorted q6 geometry to two equivalent O(6), four equivalent O(1), and four equivalent O(3) atoms. Both Eu(1)-O(6) bond lengths are 2.84 Å. All Eu(1)-O(1) bond lengths are 2.64 Å. All Eu(1)-O(3) bond lengths are 2.63 Å. In the second Eu site, Eu(2) is bonded in a distorted q6 geometry to one O(6), two equivalent O(1), two equivalent O(3), and four equivalent O(2) atoms. The Eu(2)-O(6) bond length is 2.71 Å. Both Eu(2)-O(1) bond lengths are 2.56 Å. Both Eu(2)-O(3) bond lengths are 2.55 Å. All Eu(2)-O(2) bond lengths are 2.61 Å. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(4), two equivalent O(1), and two equivalent O(2) atoms to form distorted FeO5 square pyramids that share corners with three equivalent Fe(3)O6 octahedra, corners with two equivalent Fe(2)O5 square pyramids,  a faceface with one Ba(2)O12 cuboctahedra, and faces with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 1-14°. The Fe(1)-O(4) bond length is 1.96 Å. Both Fe(1)-O(1) bond lengths are 1.98 Å. Both Fe(1)-O(2) bond lengths are 2.04 Å. In the second Fe site, Fe(2) is bonded to one O(5), two equivalent O(2), and two equivalent O(3) atoms to form FeO5 square pyramids that share corners with two equivalent Fe(3)O6 octahedra,  a cornercorner with one Fe(2)O5 square pyramid, corners with two equivalent Fe(1)O5 square pyramids, faces with two equivalent Ba(1)O12 cuboctahedra, and faces with two equivalent Ba(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 14°. The Fe(2)-O(5) bond length is 1.95 Å. Both Fe(2)-O(2) bond lengths are 2.03 Å. Both Fe(2)-O(3) bond lengths are 1.97 Å. In the third Fe site, Fe(3) is bonded to one O(4), one O(6), two equivalent O(1), and two equivalent O(3) atoms to form FeO6 octahedra that share  a cornercorner with one Fe(3)O6 octahedra, corners with two equivalent Fe(2)O5 square pyramids, corners with three equivalent Fe(1)O5 square pyramids,  a faceface with one Ba(2)O12 cuboctahedra, and faces with three equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. The Fe(3)-O(4) bond length is 2.02 Å. The Fe(3)-O(6) bond length is 1.87 Å. Both Fe(3)-O(1) bond lengths are 2.10 Å. Both Fe(3)-O(3) bond lengths are 2.10 Å. There are six inequivalent O sites. In the first O site, O(4) is bonded to one Ba(2), three equivalent Ba(1), one Fe(1), and one Fe(3) atom to form a mixture of distorted corner and edge-sharing OBa4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. In the second O site, O(5) is bonded to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Fe(2) atoms to form a mixture of distorted corner and edge-sharing OBa4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the third O site, O(6) is bonded in a distorted linear geometry to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Fe(3) atoms. In the fourth O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Ba(1), one Eu(1), one Eu(2), one Fe(1), and one Fe(3) atom. In the fifth O site, O(2) is bonded in a 6-coordinate geometry to one Ba(1), one Ba(2), two equivalent Eu(2), one Fe(1), and one Fe(2) atom. In the sixth O site, O(3) is bonded in a 6-coordinate geometry to one Ba(1), one Ba(2), one Eu(1), one Eu(2), one Fe(2), and one Fe(3) atom.