Al2(SeO4)3 crystallizes in the trigonal R-3 space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent O(1) and three equivalent O(4) atoms to form AlO6 octahedra that share corners with six equivalent Se(1)O4 tetrahedra. In the second Al site, Al(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form AlO6 octahedra that share corners with six equivalent Se(1)O4 tetrahedra. Se(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SeO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra and corners with two equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-46°. There are four inequivalent O sites. In the first O site, O(3) is bonded in a bent 150 degrees geometry to one Al(2) and one Se(1) atom. In the second O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Al(1) and one Se(1) atom. In the third O site, O(1) is bonded in a bent 150 degrees geometry to one Al(1) and one Se(1) atom. In the fourth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Al(2) and one Se(1) atom.
Al2(SeO4)3 crystallizes in the trigonal R-3 space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent O(1) and three equivalent O(4) atoms to form AlO6 octahedra that share corners with six equivalent Se(1)O4 tetrahedra. All Al(1)-O(1) bond lengths are 1.89 Å. All Al(1)-O(4) bond lengths are 1.89 Å. In the second Al site, Al(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form AlO6 octahedra that share corners with six equivalent Se(1)O4 tetrahedra. All Al(2)-O(2) bond lengths are 1.89 Å. All Al(2)-O(3) bond lengths are 1.88 Å. Se(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SeO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra and corners with two equivalent Al(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 30-46°. The Se(1)-O(1) bond length is 1.64 Å. The Se(1)-O(2) bond length is 1.63 Å. The Se(1)-O(3) bond length is 1.64 Å. The Se(1)-O(4) bond length is 1.65 Å. There are four inequivalent O sites. In the first O site, O(3) is bonded in a bent 150 degrees geometry to one Al(2) and one Se(1) atom. In the second O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Al(1) and one Se(1) atom. In the third O site, O(1) is bonded in a bent 150 degrees geometry to one Al(1) and one Se(1) atom. In the fourth O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Al(2) and one Se(1) atom.