Study of the Counter Anions in the Host‐Guest Chemistry of Cucurbit[8]uril and 1‐Ethyl‐1′‐benzyl‐4,4′‐bipyridinium

Abstract

A series of 1-ethyl-1′-benzyl-4,4′-bipyridinium compounds with different counter anions (BEV-X2, where the X is Cl, Br, I, PF6, ClO4) were synthesized. By using of NMR, MS, electrochemistry, Na2S2O4-induced redox chemistry, and UV-Vis, the role of the different counter anions in the host-guest chemistry of cucurbit[8]uril (CB[8]) was studied for the first time. The result demonstrated that BEV-X2 can form a 1 : 1 host-guest complex with CB[8] in water. Theoretical calculation further suggested that the viologen region was threaded through the cavity of CB[8], while the corresponding counter anions were located outside the cavity. Some difference can be observed on UV-Vis titration and Na2S2O4-induced redox chemistry, which showed that the counter anions have some effect on the host-guest chemistry. All these provide new insights into CB[8] host-guest system.

Concentration Effects on the First Reduction Process of Methyl Viologens and Diquat Redox Flow Battery Electrolytes

“…Besides, the presence of PF 6 – ions not only generates adsorption of species at the electrode surface but also a significant loss in reversibility. This fact is in line with previous studies that demonstrate the influence of PF 6 – ions on the electron transfer kinetics of methyl viologens. , The results exhibit a critical role of Br – and I – ions in DQ 2+ and MV 2+ structures, respectively, as they prevent adsorptive interactions of DQ +• and MV +• electrogenerated species at the glassy carbon electrode.…”

“…However, the signals obtained from the remaining compounds studied in the presence of 1 and 3 equiv of NH 4 PF 6 salt exhibited a similar behavior to the one detected for the MV bis­(hexafluorophosphate) compound dissolved in NaCl (Figure D), which is also consistent with the electrogeneration process of radical cations that attach to the electrode surface. Methyl viologens have also been extensively used in supramolecular chemistry as selective anion recognition elements. , Ji et al , studied the anion recognition of a methyl viologen derivative for ions 2Br – , 2I – and 2PF 6 – , reporting the following binding constants for interactions in a pH = 7 phosphate buffer solution: 2.37 × 10 5 , 3.37 × 10 4 and 1.92 × 10 5 mol L –1 , respectively. Based on this data and our cyclic voltammetry results, we believe that adding enough NH 4 PF 6 salt to the solutions of the compounds studied generates an ion-exchange process.…”

“…Methyl viologens have also been extensively used in supramolecular chemistry as selective anion recognition elements. 34,35 Ji et al, 34 studied the anion recognition of a methyl viologen derivative for ions 2Br − , 2I − and 2PF 6 − , reporting the following binding constants for interactions in a pH = 7 phosphate buffer solution: 2.37 × 10 5 , 3.37 × 10 4 and 1.92 × 10 5 mol L −1 , respectively. Based on this data and our cyclic voltammetry results, we believe that adding enough NH 4 PF 6 salt to the solutions of the compounds studied generates an ion-exchange process.…”