10-Methyl- and 9,10-dimethylacridinium methyl sulfate.

The title compounds, C(14)H(12)N(+).CH(3)O(4)S(-), (I), and C(15)H(14)N(+).CH(3)O(4)S(-), (II), respectively, crystallize with the planar 10-methylacridinium or 9,10-dimethylacridinium cations arranged in layers, parallel to the twofold axis in (I) and perpendicular to the 2(1) axis in (II). Adjacent cations in both compounds are packed in a 'head-to-tail' manner. The methyl sulfate anion only exhibits planar symmetry in (II). The cations and anions are linked through C-H.O interactions involving three O atoms of the anion, six acridine H atoms and the CH(3) group on the N atom in (I), and the four O atoms of the anion, three acridine H atoms and the carbon-bound CH(3) group in (II). The methyl sulfate anions are oriented differently in the two compounds relative to the cations, being nearly perpendicular in (I) but parallel in (II). Electrostatic interaction between the ions and the network of C-H.O interactions leads to relatively compact crystal lattices in both structures.