Voltammetric and impedance study of the binding of ferrocene derivatives to a sulfonated calix[6]arene host in aqueous solutions

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Vol. 523; no. 1; pp. 126 - 135
• Main Authors: Komura, T, Yamaguchi, T, Kura, K, Tanabe, J
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 19.04.2002; Elsevier Science
• Subjects: Calixarene- p-hexasulfonate; Chemistry; Exact sciences and technology; Ferrocene derivatives; General and physical chemistry; Host–guest interaction; Inclusion compound; Redox-switchable supramolecular system; Solution properties; Solutions; Ferrocene derivatives; Redox-switchable supramolecular system; Inclusion compound; Host–guest interaction; Calixarene- p-hexasulfonate; Electrochemical potential; Ionic conductivity; Association constant; Calixarene; Experimental study; Metallocene; Cyclic voltammetry; Iron Organic compounds; Electrochemical properties; Thermodynamic parameter; Molecular complex; Kinetic parameter; Redox potential; Chemical properties; Aqueous solution
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/S0022-0728(02)00739-8

This report describes the effect of host–guest complexation on the thermodynamic and kinetic parameters of ferrocene redox reactions in aqueous media. The formal potentials of the ferrocene/ferrocenium couples examined shifted to less positive values with increasing calixarene concentration, because of the formation of a 1:1 inclusion compound. The order of binding constants was cationic ferrocene≫non-charged ferrocene>anionic ferrocene. The oxidized form with a higher positive charge was bound more strongly to the host than was the corresponding reduced form. The result was contrary to that observed for β-cyclodextrin. The inclusion compounds formed by sulfonated calix[6]arene were greatly stabilized by an electrostatic interaction between the negatively charged host and cationic guest. Fast-scan voltammetric behavior suggested that inclusion-ejection processes practically attain equilibrium in the scan-rate range below 2 V s −1. Randles plots for the Faradaic impedance of the electrode reaction virtually comprised two nearly parallel straight lines with a small separation over the frequency range of 10 2−10 −3 Hz, indicating negligible chemical reaction impedance. As the host concentration increased, the mean diffusion coefficient of the (ferrocenylmethyl)trimethylammonium cation decreased inversely proportionally from 6.0×10 −6 cm 2 s −1 of the free ion to (2.1±0.2)×10 −6 cm 2 s −1 of the corresponding inclusion complex. The result of the impedance analysis suggests that the included guest exchanges no electrons directly with the electrode.