Stability and molecular and crystal structure of 9-amino-10-methylacridinium triiodide

Mixing of equimolar amounts of 9-amino-10-methylacridinium iodide and elemental iodine yields 9-amino-10-methylacridinium triiodide. The complexation in the organic cation iodide-elemental iodine system has been studied by spectrophotometry. The composition and the stability constant of the complex formed in a chloroform solution have been determined. The compound [C14H13N2]+[I3]− has been isolated as dark red plate crystals and studied by X-ray diffraction. The structure is formed by linear I 3 − anions and 9-amino-10-methylacridinium cations assembled through π-π stacking. The cations in the stacks are shifted by approximately one ring with respect to one another. The triiodide ion is linear, the average I-I bond length (2.915 Å) is close to the standard value. The stacking reflects the specific nature of the organic cation, while the presence of the I 3 − counterion results in extension of the system of hydrogen bonds.