KAl(SO4)2 crystallizes in the trigonal P-3m1 space group. K(1) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form KO12 cuboctahedra that share edges with six equivalent K(1)O12 cuboctahedra, edges with six equivalent S(1)O4 tetrahedra, and faces with two equivalent Al(1)O6 octahedra. Al(1) is bonded to six equivalent O(1) atoms to form AlO6 octahedra that share corners with six equivalent S(1)O4 tetrahedra and faces with two equivalent K(1)O12 cuboctahedra. S(1) is bonded to one O(2) and three equivalent O(1) atoms to form SO4 tetrahedra that share corners with three equivalent Al(1)O6 octahedra and edges with three equivalent K(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 17°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one K(1), one Al(1), and one S(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to three equivalent K(1) and one S(1) atom.
KAl(SO4)2 crystallizes in the trigonal P-3m1 space group. K(1) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form KO12 cuboctahedra that share edges with six equivalent K(1)O12 cuboctahedra, edges with six equivalent S(1)O4 tetrahedra, and faces with two equivalent Al(1)O6 octahedra. All K(1)-O(1) bond lengths are 3.01 Å. All K(1)-O(2) bond lengths are 2.95 Å. Al(1) is bonded to six equivalent O(1) atoms to form AlO6 octahedra that share corners with six equivalent S(1)O4 tetrahedra and faces with two equivalent K(1)O12 cuboctahedra. All Al(1)-O(1) bond lengths are 1.87 Å. S(1) is bonded to one O(2) and three equivalent O(1) atoms to form SO4 tetrahedra that share corners with three equivalent Al(1)O6 octahedra and edges with three equivalent K(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 17°. The S(1)-O(2) bond length is 1.44 Å. All S(1)-O(1) bond lengths are 1.47 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one K(1), one Al(1), and one S(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to three equivalent K(1) and one S(1) atom.