A study of the interaction between inverted cucurbit[6]uril and symmetric viologens

Abstract

The interaction between inverted cucuribit[6]uril (iQ[6]) and a series of symmetric viologens bearing aliphatic substituents, namely dicationic dialkyl-4,4′-bipyridinium guests where the alkyl substituent is CH₃(CH₂)_n (n = 1, 3 and 5) or benzyl, has been studied in aqueous solution by ¹H NMR spectroscopy, electronic absorption spectroscopy, isothermal titration calorimetry and mass spectrometry. The viologen bearing C₆H₅CH₂ substituents has also been investigated. In the case of the dialkyl-derived guests, single crystal X-ray diffraction, on crystals grown in the presence of CdCl₂, revealed the compositions to be 2(C₃₆H₃₆N₂₄O₁₂), 4(C₁₄H₁₈N₂), Cd₅Br₉.₅₆C_l10.₄₄2(H₂O)·2(H₃O); 2(C₃₆H₃₆N₂₄O₁₂), C₁₈H₂₆N₂,2(CdCl₄), 36H₂O and 2(C₃₆H₃₆N₂₄O₁₂), 2(C₁₁H₁₇N), 2(CdCl₄), 20H₂O for the use of n = 1, 3 or 5 respectively. Thus, in the solid state, in the case of both BV²⁺ (n = 3) and HV²⁺ (n = 5), an interaction of viologen with iQ[6] was observed and the structure adopted is an external ‘dumbbell-type’ structure.