Al2Se3 is beta indium sulfide structured and crystallizes in the tetragonal I4_1/amd space group. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form corner-sharing AlSe4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-64°. In the second Al site, Al(2) is bonded to one Se(1), two equivalent Se(3), and three equivalent Se(2) atoms to form AlSe6 octahedra that share corners with four equivalent Al(1)Se4 tetrahedra, edges with two equivalent Al(3)Se6 octahedra, and edges with four equivalent Al(2)Se6 octahedra. In the third Al site, Al(3) is bonded to two equivalent Se(3) and four equivalent Se(1) atoms to form AlSe6 octahedra that share corners with four equivalent Al(1)Se4 tetrahedra, edges with two equivalent Al(3)Se6 octahedra, and edges with four equivalent Al(2)Se6 octahedra. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one Al(1), one Al(2), and two equivalent Al(3) atoms. In the second Se site, Se(2) is bonded to one Al(1) and three equivalent Al(2) atoms to form a mixture of distorted corner and edge-sharing SeAl4 tetrahedra. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Al(3) and two equivalent Al(2) atoms.
Al2Se3 is beta indium sulfide structured and crystallizes in the tetragonal I4_1/amd space group. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form corner-sharing AlSe4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-64°. Both Al(1)-Se(1) bond lengths are 2.44 Å. Both Al(1)-Se(2) bond lengths are 2.42 Å. In the second Al site, Al(2) is bonded to one Se(1), two equivalent Se(3), and three equivalent Se(2) atoms to form AlSe6 octahedra that share corners with four equivalent Al(1)Se4 tetrahedra, edges with two equivalent Al(3)Se6 octahedra, and edges with four equivalent Al(2)Se6 octahedra. The Al(2)-Se(1) bond length is 2.60 Å. Both Al(2)-Se(3) bond lengths are 2.51 Å. There is one shorter (2.60 Å) and two longer (2.70 Å) Al(2)-Se(2) bond lengths. In the third Al site, Al(3) is bonded to two equivalent Se(3) and four equivalent Se(1) atoms to form AlSe6 octahedra that share corners with four equivalent Al(1)Se4 tetrahedra, edges with two equivalent Al(3)Se6 octahedra, and edges with four equivalent Al(2)Se6 octahedra. Both Al(3)-Se(3) bond lengths are 2.53 Å. All Al(3)-Se(1) bond lengths are 2.61 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a rectangular see-saw-like geometry to one Al(1), one Al(2), and two equivalent Al(3) atoms. In the second Se site, Se(2) is bonded to one Al(1) and three equivalent Al(2) atoms to form a mixture of distorted corner and edge-sharing SeAl4 tetrahedra. In the third Se site, Se(3) is bonded in a distorted T-shaped geometry to one Al(3) and two equivalent Al(2) atoms.