Crystal structure of anhydrous aluminum sulfate.

Abstract

The detailed crystal structure of anhydrous aluminum sulfate, Al2(SO4)3, has been determined from X-ray powder diffraction with well crystallized powder sample. The grain was rhombohedron in shape and surrounded by crystal-faces of {0 1 1 2} planes. The unit cell was assigned to hexagonal symmetry with a0=8.032Å, c0=21.360Å and Z=6, and the space group C3i2-R3.All the atomic parameters were determined by purely geometrical calculations with some assumptions. The calculated intensities of the diffractions from the parameters were in good agreement with the observed ones.Each S atom forms a regular SO4 tetrahedron. The orientation of the SO4 tetrahedron within the unit cell is such that one of the twofold symmetry axes is parallel to the (00l) planes and makes an angle of 16° to one of the a-axis, and the two edges perpendicular to this symmetry axis are inclined at about 80° and 10° respectively to the (00l) planes.Each Al atom is surrounded with the six SO4 tetrahedra and coordinates six O atoms by taking one O atom per one SO4 tetrahedron. The AlO6 octahedra are slightly distorted and classified into two kinds with shape and symmetry.