Hexaaqua­aluminium(III) tris­(methane­sulfonate)

The title compound, [Al(H₂O)₆](CH₃SO₃)₃ (common name: aluminium methane­sulfonate hexa­hydrate), was crystallized from an aqueous solution prepared by the precipitation reaction of aluminium sulfate and barium methane­sulfonate. Its crystal structure is the first of the boron group methane­sulfonates to be determined. The characteristic building block is a centrosymmetric unit containing two hexa­aqua­aluminium cations that are connected to each other by two O atoms of the –SO₃ groups in an O—H...O...H—O sequence. Further O—H...O hydrogen bonding links these blocks in orthogonal directions – along [010] forming a double chain array, along [10-1] forming a layered arrangement of parallel chains and along [101] forming a three-dimensional network. As indicated by the O...O distances of 2.600 (3)–2.715 (3) Å, the hydrogen bonds are from medium–strong to strong. A further structural feature is the arrangement of two and four methyl groups, respectively, establishing `hydro­phobic islands' of different size, all positioned in a layer-like region perpendicular to [101]. The only other building block within this region is one of the –SO<sub>3</sub> groups giving a local connection between the hydro­philic structural regions on both sides of the `hydro­phobic' one. Thermal analysis indicates that a stepwise dehydration process starts at about 413 K and proceeds via the respective penta- and dihydrate until the compound completely decomposes at about 688 K.