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

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),Cd5Br9.56Cl10.442(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