Ionic interactions in the oligoviologens–K4Fe(CN)6 system

Abstract Various oligoviologen derivatives were synthesized by Menshutkin reaction of 4,4′-bipyridine ( BPy ) with α,ω-dibromoalkanes (α,ω– C n H 2n Br 2 ) in acetonitrile medium. 1H NMR analysis demonstrated that the degree of polymerization increases with alkyl chain length and reaction time, reaching its maximum at the molar reagent ratio (α,ω–C n H 2n Br 2 /BPy) of 1.2: 1. The obtained oligomers and their interaction with [Fe(CN) 6 ] 4 − anions were characterized by 1H NMR, cyclic voltammetry, electronic absorption spectroscopy and EDX analysis. Two principally different types of interaction between low molecular weight oligoviologens and hexacyanoferrate ions were established: 1) fast reversible outer-sphere charge transfer complex formation and 2) slow irreversible reaction, presumably corresponding to the inner-sphere complex [Fe(CN) 5 L] q ± formation. Oligoviologens with medium molecular weight were found to form a poorly soluble product with [Fe(CN) 6 ] 4 − ions, which can be redissolved again by the addition of halide ions.