Abstract: Inclusion complexation between cucurbit[n]uril(CB[n], n=5,6,7,8) and two diazonuim salts in various acid solutions was investigated by ¹H NMR spectroscopy and UV-Vis spectrophotometric titration. The binding constants were obtained by using a non-linear least squares curve fitting. The inclusion of diazonuim ions in the cavity of CB[n] made ¹H NMR spectra of diazonuim ions moving towards a higher magnetic field. The results indicated that CB[5] and CB[8] couldn′t include the two kinds of diazonium ions efficiently. The cavity of CB[6] was too small to accommodate 4,4′-biphenylene-bis-diazonium ions. CB[7] could contain both p-methylbenzene diazonium and 4,4′-biphenylene-bis-diazonium ions. In contrast to CB[6], CB[7] was more suitable for holding p-methylbenzenediazonium ion, showing that the complex stability is dominated by the size/shape-matching between the host and guest. With increasing the concentration of the acid, the measured binding constants decreased notablely, due to the competitive complex of protons with carbonyls of CB[n].

Key words: Cucurbit[n]uril, Inclusion complexation, Diazonium salts, Molecular recognition