Crystal structure and lattice energetics of 10-methylacridinium halides

The crystal structures of 10-methylacridinium chloride monohydrate, bromide monohydrate and iodide were determined by X-ray analysis. The compounds cr ystallize in the triclinic space group, P (1) over bar, with 2 molecules in the unit cell. The molecular arrangement in the crystals revealed that hyd rogen bonds (in hydrates) and van der Waals contacts play a significant par t in intermolecular interactions. To discover their nature, contributions t o the crystal lattice energy arising from electrostatic (the most important since the compounds form ionic crystals), dispersive and repulsive interac tions were calculated. Enthalpies of formation of the salts, their stabilit y and susceptibility to decomposition could be predicted from a combination of crystal lattice energies with values of other thermochemical characteri stics obtained theoretically or taken from the literature. The role of wate r in the stabilization of the crystal lattice of the hydrates is also expla ined. The information gathered has given an insight into the features and b ehaviour of compounds which can be regarded as models of a large group of a romatic quaternary nitrogen salts.