Al2Se3 crystallizes in the monoclinic Cc space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form corner-sharing AlSe4 tetrahedra. In the second Al site, Al(2) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form corner-sharing AlSe4 tetrahedra. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one Al(2) and two equivalent Al(1) atoms. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to one Al(1) and two equivalent Al(2) atoms.
Al2Se3 crystallizes in the monoclinic Cc space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one Se(1), one Se(3), and two equivalent Se(2) atoms to form corner-sharing AlSe4 tetrahedra. The Al(1)-Se(1) bond length is 2.31 Å. The Al(1)-Se(3) bond length is 2.43 Å. There is one shorter (2.43 Å) and one longer (2.44 Å) Al(1)-Se(2) bond length. In the second Al site, Al(2) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form corner-sharing AlSe4 tetrahedra. The Al(2)-Se(1) bond length is 2.32 Å. The Al(2)-Se(2) bond length is 2.45 Å. There is one shorter (2.43 Å) and one longer (2.45 Å) Al(2)-Se(3) bond length. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the second Se site, Se(2) is bonded in a trigonal non-coplanar geometry to one Al(2) and two equivalent Al(1) atoms. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to one Al(1) and two equivalent Al(2) atoms.