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This paper describes the X-ray crystal structure of a complex of acridino-18-crown-6 ether (S,S)-2 and sodium perchlorate. The structure shows a homodimer in the crystal and suggests the potential for π–π bonded interactions between the monomers. The average distance of the two tricyclic units (3.49 ± 0.1 A) may indicate a considerably strong π–π interaction. Fluorescence titration was performed in order to determine the stoichiometry and stability constant (K s) of the sodium ion-(S,S)-2 complex. Based on the global fitting of the fluorescence spectra, we suggest the formation of a complex with 1:1 ligand to metal ion ratio, and the logK value determined by nonlinear regression analysis was 5.23.

This paper describes the X-ray crystal structure of the diastereomeric complexes formed by enantiopure dimethyl-substituted acridino-18-crown-6 ether (R,R)-1 and the enantiomers of 1-(1-naphthyl)ethylammonium perchlorate. We found that the heterochiral complex (R,R)-1–(S)-1-NEA is more stable than the homochiral one (R,R)-1–(R)-1-NEA. In the case of the heterochiral complex, the X-ray studies revealed a strong intermolecular π–π interaction between the naphthyl unit and the acridine moiety. However, in the case of the homochiral complex, π–π interaction was not found. We suggest that the existence or absence of the π–π interaction and the difference in steric repulsions in the diastereomers is responsible for the enantiomeric discrimination.

This paper describes the X-ray crystal structure of a complex of acridono-18-crown-6 ether 3 and lead(II) perchlorate. The structure shows a π–π bonded heterodimer in the crystal. One part of the dimer moves to 9-hydroxyacridine tautomeric form upon lead(II) complexation, in which the lead(II) ion is eight-coordinated and fits well into the cavity of the macrocycle. The other part of the dimer stays in the 9(10H)-acridone tautomeric form, which favors water complexation. The average bond distance of the two tricyclic units (3.5 A) indicates a strong π–π interaction. The X-ray studies also revealed a cation–π interaction between lead(II) and the electron-rich acridone moiety.