The melting points and melting enthalpies of nine phenyl acridine-9-carboxylates—nitro-, methoxy- or halogen-substituted in
the phenyl fragment—and their 9-phenoxycarbonyl-10-methylacridinium trifluoromethanesulphonate derivatives were determined
by DSC. The volatilisation temperatures and enthalpies of phenyl acridine-9-carboxylates were either measured by DSC or obtained
by fitting TG curves to the Clausius–Clapeyron relationship. For the compounds whose crystal structures are known, crystal
lattice energies and enthalpies were determined computationally as the sum of electrostatic, dispersive and repulsive interactions.
By combining the enthalpies of formation of gaseous phenyl acridine-9-carboxylates or 9-phenoxycarbonyl-10-methylacridinium
trifluoromethanesulphonate ions, obtained by the DFT method, and the corresponding enthalpies of sublimation and/or crystal
lattice enthalpies, the enthalpies of formation of the compounds in the solid phase were predicted. In the case of the phenyl
acridine-9-carboxylates, the computationally predicted crystal lattice enthalpies correspond reasonably well with the experimentally
obtained enthalpies of sublimation. The crystal lattices of phenyl acridine-9-carboxylates are stabilised predominantly by
dispersive interactions between molecules, whilst the crystal lattices of their quaternary salts are stabilised by electrostatic
interactions between ions.