Endo-cavity Complexes between Calix[6]arene Dianions and Aliphatic Ammonium Cations: Structure of a Hexylammonium Complex by X-ray Crystallography

• Published in: Supramolecular chemistry Vol. 16; no. 6; pp. 453 - 458
• Main Authors: Nachtigall, Francine F., Lazzarotto, Márcio, Castellano, Eduardo Ernesto, Nome, Faruk
• Format: Journal Article
• Language: English
• Published: Taylor & Francis GroupAbingdon, UK 01-09-2004
• Subjects: Ammonium cations; Calixarenes; Inclusion compounds; Molecular recognition
• ISSN: 1061-0278; 1029-0478
• DOI: 10.1080/10610270410001717192

The interactions of calix[6]arene and p-tert-butylcalix[6]arene with aliphatic amines in acetonitrile solution were studied by spectrophotometric titrations in the UV region and
1
H NMR spectrometry. Calix[6]arenes can undergo two deprotonations by aliphatic amines and the extent of the second proton transfer is mainly governed by the size of the α-substituent of the amine.
1
H NMR spectra show that the macrocycle adopts a 1,2,3-alternate conformation and that the α-hydrogens of the ammonium ions are shielded by the π-clouds of the aromatic rings. The X-ray crystal structure of the dihexylammonium complex of the p-tert-butylcalix[6]arene dianion, reported here, confirms the 1,2,3-alternate conformation and shows one of the two ammonium moieties encapsulated in the inner cavity of the macrocycle.