Al5Se8 is beta indium sulfide-like structured and crystallizes in the cubic F-43m space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form AlSe6 octahedra that share corners with three equivalent Al(2)Se4 tetrahedra and edges with six equivalent Al(1)Se6 octahedra. In the second Al site, Al(2) is bonded to four equivalent Se(2) atoms to form corner-sharing AlSe4 tetrahedra. The corner-sharing octahedral tilt angles are 61°. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded to one Al(2) and three equivalent Al(1) atoms to form a mixture of distorted edge and corner-sharing SeAl4 tetrahedra. In the second Se site, Se(1) is bonded in a distorted T-shaped geometry to three equivalent Al(1) atoms.
Al5Se8 is beta indium sulfide-like structured and crystallizes in the cubic F-43m space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form AlSe6 octahedra that share corners with three equivalent Al(2)Se4 tetrahedra and edges with six equivalent Al(1)Se6 octahedra. All Al(1)-Se(1) bond lengths are 2.51 Å. All Al(1)-Se(2) bond lengths are 2.66 Å. In the second Al site, Al(2) is bonded to four equivalent Se(2) atoms to form corner-sharing AlSe4 tetrahedra. The corner-sharing octahedral tilt angles are 61°. All Al(2)-Se(2) bond lengths are 2.45 Å. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded to one Al(2) and three equivalent Al(1) atoms to form a mixture of distorted edge and corner-sharing SeAl4 tetrahedra. In the second Se site, Se(1) is bonded in a distorted T-shaped geometry to three equivalent Al(1) atoms.