9-[(Mesityloxy)carbonyl]-10-methylacridinium trifluoromethanesulphonate and its derivative mesityl 9-methoxy-10-methyl-9,10-dihydroacridine-9-carboxylate: Structural and physicochemical features

At room temperature, 9-[(mesityloxy)carbonyl]-10-methylacridinium trifluoromethanesulphonate (1) and mesityl 9-methoxy-10-methyl-9,10-dihydroacridine-9-carboxylate (2) both form monoclinic crystals in space group P21/n with Z = 4. The crystal structure of 1 is stabilised by long-range electrostatic interactions, as well as by a network of short-range C–H⋯O, C–H⋯F, C–H⋯π, C–F⋯π and π–π interactions between cations or cations and anions. Compound 2 forms molecular crystals stabilised by a network of short-range C–H⋯O and non-specific dispersive interactions. The acridine skeleton in the cation of 1 is almost planar, whereas in 2 it is folded along the C9⋯N10 axis, giving rise to a ‘butterfly’ type geometry. Computations at the DFT level predict that mesityl acridine-9-carboxylate reacts spontaneously with methyl trifluoromethanesulphonate to yield 1. At the same level of theory it was found that 2 should be formed following the attack of a complex anion, formed from methyl trifluoromethanesulphonate and the trifluoromethanesulphonate anion, on C9 of the 9-[(mesityloxy)carbonyl]-10-methylacridinium cation. The thermodynamic and kinetic (transition state) characteristics of the processes leading to 1 and 2 were predicted. The structural and physicochemical features of the entities containing acridine nuclei are analysed and compared from the point of view of their chemical behaviour.