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 CH 3 (CH 2 ) n ( n = 1, 3 and 5) or benzyl, has been studied in aqueous solution by 1 H NMR spectroscopy, electronic absorption spectroscopy, isothermal titration calorimetry and mass spectrometry. The viologen bearing C 6 H 5 CH 2 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 CdCl 2 , revealed the compositions to be 2(C 36 H 36 N 24 O 12 ), 4(C 14 H 18 N 2 ), Cd 5 Br 9 . 56 C l10 . 44 2(H 2 O)·2(H 3 O); 2(C 36 H 36 N 24 O 12 ), C 18 H 26 N 2 ,2(CdCl 4 ), 36H 2 O and 2(C 36 H 36 N 24 O 12 ), 2(C 11 H 17 N), 2(CdCl 4 ), 20H 2 O for the use of n = 1, 3 or 5 respectively. Thus, in the solid state, in the case of both BV 2+ ( n = 3) and HV 2+ ( n = 5), an interaction of viologen with iQ[6] was observed and the structure adopted is an external ‘dumbbell-type’ structure.