Synthesis and crystal structures of [Al(H2O)6](SO4)NO3•2H2O and [Al(H2O)6](SO4)Cl•H2O

Two novel aluminium double salts, [Al(H2O)(6)](SO4)NO3 center dot 2H(2)O, hexaqua-aluminium sulfate nitrate dihydrate, (1), and [Al(H2O)(6)](SO4)Cl center dot H2O, hexaqua-aluminium sulfate chloride hydrate, (2), were obtained in the form of single crystals. Their crystal structures are each based on an octahedral [Al(H2O)(6)](3+) unit and both structures have in common one charge-balancing SO42- anion. The final positive charge from the aluminium(III) cation is balanced by an NO3- or a Cl- anion for (1) and (2), respectively. Compound (1) further contains two unligated water molecules while compound (2) only contains one unligated water molecule. In the crystal structures, all components are spatially separated and interactions are mediated via medium-strong hydrogen bonding, compared to many other reported aluminium sulfates where corner-sharing of the building units is common. The two compounds represent rare cases where one aluminium(III) cation is charge-balanced by two different anions.