The crystal structure of hydriodide of 9(10-methyl)-acridinimine, the cation of which originates from the imino tautomeric form of 9-acridinamine, was determined by X-ray analysis (monoclinic; space group P2(1)/c; Z=4; R=0.0368 for 1651 observed reflections). The bond between the egzocyclic N atom and the acridine moiety retains a length typical for double bonds, while lengths of adjacent C-C bonds are contained between those characteristic for single and aromatic bonds. The central ring system is strongly conjugated with the side rings through bonds at the endocyclic N atom which results in the acridine skeleton being almost planar. For this molecule and fifteen halide salts of simple nitrogen organic bases, the electrostatic, dispersive and repulsive contributions to the lattice energy were evaluated, boiling down the problem of intermolecular interactions to atom - atom interactions. Coulombic energies arising from charges fitted to the molecular electrostatic potential on the DFT level, compare well with experimental values of the crystal lattice energy and show a decreasing tendency with growth of dimensions (volume of a stoichiometric unit) of interacting ions.