The molecular complex formation of six macrocyclic and six acyclic polyethers with tropylium and 4‐methoxyphenyltropylium tetrafluoroborates was observed and characterized in the gas phase by fast atom bombardment mass spectrometry (FABMS), to obtain information on intrinsic molecular interactions in the absence of the complicating effect of solvation. The stoichiometry of the complexes was assessed on the basis of corresponding peaks in FAB mass spectra. In addition to the expected 1 : 1 complexes between polyether and tropylium ion, some 2 : 1 complexes were also formed. The stability order of selected complexes was studied in competition experiments. The complexation equilibrium constant and thermodynamic parameters for the interaction of dibenzo‐18‐crown‐6 with tropylium ion were determined in 1,2‐dichloroethane solution by UV‐visible spectrophotometry. Complexation of polyethers with tropylium salts has not been reported previously.
Inclusion complex formation between benzene-substituted crown ethers and electron-deficient pyridinium ions was studied by crystallographic and NMR methods. The major attractive host ± guest interactions in these complexes are face-to-face aromatic ± aromatic and cation ± p interactions. In addition, the crystal structures show that hydrogen bonding influences the complexation of cations. Individual studies of the binding strength as a function of host, guest, and solvent were carried out. Four pyridinium guests were prepared for the investigation. Fast atom bombardment (FAB) mass spectrometry was used to determine the stoichiometry of the complexes. The stability constants were measured by 1 H NMR and the structures of the complexes in acetonitrile are discussed. X-ray crystal structures were determined for complexes of dibenzo-18-crown-6 with pyridinium tetrafluoroborate (2 B18C 6 ± PyBF 4 ) and dibenzo-18-crown-6 with 1-aminopyridinium tetrafluoroborate (2 B18C 6 ± 1-NH 2 PyBF 4 ).
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