9-(2,6-dichlorophenoxycarbonyl)-10-methylacridinium trifluoromethanesulfonate and its precursor 2,6-dichlorophenyl acridine-9-carboxylate.

The title compounds, C21H14Cl2NO2+.CF3O3S-, (I), and C20H11Cl2NO2, (II), form triclinic crystals. Adjacent cations of (I) are oriented either parallel or antiparallel; in the latter case, they are related by a centre of symmetry. Together with the CF3SO3- anions, the antiparallel-oriented cations of (I) form layers in which the molecules are linked via a network of C-H...O and pi-pi interactions (between the benzene rings). These layers, in turn, are linked via a network of multidirectional pi-pi interactions between the acridine rings, and the whole lattice is stabilized by electrostatic interactions between ions. Adjacent molecules of (II) are oriented either parallel or antiparallel; in the latter case, they are related by a centre of symmetry. Parallel-oriented molecules are arranged in chains stabilized via C-H...Cl interactions. These chains are oriented either parallel or antiparallel and are stabilized, in the latter case, via multidirectional pi-pi interactions and more generally via dispersive interactions. Acridine and independent benzene moieties lie parallel in the lattices of (I) and (II), and are mutually oriented at an angle of 33.4 (2) degrees in (I) and 9.3 (2) degrees in (II).