Eu3Al2O7 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 9-coordinate geometry to four equivalent O(1) and five equivalent O(2) atoms. In the second Eu site, Eu(2) is bonded to four equivalent O(3) and eight equivalent O(1) atoms to form EuO12 cuboctahedra that share corners with four equivalent Eu(2)O12 cuboctahedra, faces with four equivalent Eu(2)O12 cuboctahedra, and faces with eight equivalent Al(1)O6 octahedra. Al(1) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form AlO6 octahedra that share corners with five equivalent Al(1)O6 octahedra and faces with four equivalent Eu(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-2°. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Al(1) atoms to form distorted OEu4Al2 octahedra that share corners with four equivalent O(3)Eu4Al2 octahedra, corners with six equivalent O(2)Eu5Al octahedra, corners with eight equivalent O(1)Eu4Al2 octahedra, edges with three equivalent O(1)Eu4Al2 octahedra, faces with two equivalent O(3)Eu4Al2 octahedra, faces with two equivalent O(2)Eu5Al octahedra, and faces with four equivalent O(1)Eu4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-61°. In the second O site, O(2) is bonded to five equivalent Eu(1) and one Al(1) atom to form distorted OEu5Al octahedra that share  a cornercorner with one O(3)Eu4Al2 octahedra, corners with four equivalent O(2)Eu5Al octahedra, corners with twelve equivalent O(1)Eu4Al2 octahedra, edges with eight equivalent O(2)Eu5Al octahedra, and faces with four equivalent O(1)Eu4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-53°. In the third O site, O(3) is bonded to four equivalent Eu(2) and two equivalent Al(1) atoms to form distorted OEu4Al2 octahedra that share corners with two equivalent O(2)Eu5Al octahedra, corners with four equivalent O(3)Eu4Al2 octahedra, corners with sixteen equivalent O(1)Eu4Al2 octahedra, edges with four equivalent O(3)Eu4Al2 octahedra, and faces with eight equivalent O(1)Eu4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-61°. In the fourth O site, O(3) is bonded to four equivalent Eu(2) and two equivalent Al(1) atoms to form distorted OEu4Al2 octahedra that share corners with two equivalent O(2)Eu5Al octahedra, corners with four equivalent O(3)Eu4Al2 octahedra, corners with sixteen equivalent O(1)Eu4Al2 octahedra, edges with four equivalent O(3)Eu4Al2 octahedra, and faces with eight equivalent O(1)Eu4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-61°.
Eu3Al2O7 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 9-coordinate geometry to four equivalent O(1) and five equivalent O(2) atoms. All Eu(1)-O(1) bond lengths are 2.50 Å. There is one shorter (2.35 Å) and four longer (2.64 Å) Eu(1)-O(2) bond lengths. In the second Eu site, Eu(2) is bonded to four equivalent O(3) and eight equivalent O(1) atoms to form EuO12 cuboctahedra that share corners with four equivalent Eu(2)O12 cuboctahedra, faces with four equivalent Eu(2)O12 cuboctahedra, and faces with eight equivalent Al(1)O6 octahedra. All Eu(2)-O(3) bond lengths are 2.63 Å. All Eu(2)-O(1) bond lengths are 2.67 Å. Al(1) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form AlO6 octahedra that share corners with five equivalent Al(1)O6 octahedra and faces with four equivalent Eu(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Al(1)-O(2) bond length is 2.02 Å. The Al(1)-O(3) bond length is 1.88 Å. All Al(1)-O(1) bond lengths are 1.86 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Al(1) atoms to form distorted OEu4Al2 octahedra that share corners with four equivalent O(3)Eu4Al2 octahedra, corners with six equivalent O(2)Eu5Al octahedra, corners with eight equivalent O(1)Eu4Al2 octahedra, edges with three equivalent O(1)Eu4Al2 octahedra, faces with two equivalent O(3)Eu4Al2 octahedra, faces with two equivalent O(2)Eu5Al octahedra, and faces with four equivalent O(1)Eu4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-61°. In the second O site, O(2) is bonded to five equivalent Eu(1) and one Al(1) atom to form distorted OEu5Al octahedra that share  a cornercorner with one O(3)Eu4Al2 octahedra, corners with four equivalent O(2)Eu5Al octahedra, corners with twelve equivalent O(1)Eu4Al2 octahedra, edges with eight equivalent O(2)Eu5Al octahedra, and faces with four equivalent O(1)Eu4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-53°. In the third O site, O(3) is bonded to four equivalent Eu(2) and two equivalent Al(1) atoms to form distorted OEu4Al2 octahedra that share corners with two equivalent O(2)Eu5Al octahedra, corners with four equivalent O(3)Eu4Al2 octahedra, corners with sixteen equivalent O(1)Eu4Al2 octahedra, edges with four equivalent O(3)Eu4Al2 octahedra, and faces with eight equivalent O(1)Eu4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-61°. In the fourth O site, O(3) is bonded to four equivalent Eu(2) and two equivalent Al(1) atoms to form distorted OEu4Al2 octahedra that share corners with two equivalent O(2)Eu5Al octahedra, corners with four equivalent O(3)Eu4Al2 octahedra, corners with sixteen equivalent O(1)Eu4Al2 octahedra, edges with four equivalent O(3)Eu4Al2 octahedra, and faces with eight equivalent O(1)Eu4Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-61°. All O(3)-Eu(2) bond lengths are 2.63 Å. Both O(3)-Al(1) bond lengths are 1.88 Å.