Comparative study of non-covalent interactions between cationic N-phenylviologens and halides by electrochemistry and NMR: the halogen bonding effect

Five N-phenylviologen (PV2+) derivatives have been synthesized and their electrochemical behavior in the presence of halide anions has been studied. Further investigations were carried out by H-1 and F-19 NMR spectroscopy at different chloride concentrations. This is the first time a systematic study combines cyclic voltammetry and NMR spectroscopy in order to analyse the contribution of halogen bonding among the various non-covalent interactions between iodinated N-phenylviologens. The results show strong evidence for a significant halogen bonding effect in the interaction between halides and the iodo-tetrafluoro-phenylviologen PV2+-C6F4I. A significant influence of halogen bonding on reduction potentials of the novel halogen bond donor PV2+-C6F4I has been evidenced resulting in the first example of inverse redox switching of an XB-donor being partially deactivated upon reduction. Furthermore the particular binding properties of the perfluorinated derivative PV2+-C6F5 towards chloride are discussed considering a possible contribution of pi-anion interaction in solution.