On the Nature of Solvent Effects on Redox Properties

Abstract

The one-electron reduction potentials of six radical cations, four cations, and four neutral radicals in tetrahydrofuran, dichloromethane, dimethyl sulfoxide, N-methyl-2-pyrrolidinone, N,N-dimethylformamide, acetonitrile, methanol, ethanol, 2-propanol, acetone, formamide, and 1,1,1,3,3,3-hexafluoropropan-2-ol have been measured by cyclic voltammetry. For 10 of the redox couples, the redox process was reversible in all solvents. These results have been used to evaluate solvent effects by means of the Kamlet-Taft relationship. The relative importance of the solvent parameters R, β, π*, and δ H is 54.9, 9.6, 15.5 and 20.0%, respectively, for the radical cation displaying the strongest solvent dependence. In addition, we have studied the entropy contribution to some of the observed solvent effects by measuring the redox potentials as a function of temperature. The absolute value of the entropy appears to increase with increasing hydrogen bond donor ability of the solvent. The variation in entropy indicates that specific solvation is of main importance when considering solvent effects on redox properties.

(η4-Tetraarylcyclobutadiene)(η5-formylcyclopentadienyl)cobalt(I) complexes: Facilities to finetune the electron-donating capability in dipolar organometallics

“…The cyclic voltammogram for 1e displays three irreversible oxidation waves. The one with the highest oxidation potential (E pa = 550 + 5 mV vs. FcH/FcH + ) is assigned to an oxidation of the p-dimethylamino phenyl substituents in agreement with published data of p-dimethylamino benzene [19]. Due to the number of aryl substituents in 1e the corresponding peak current is almost three times as large as the peak current of the first oxidation at E pa = À2 + 5 mV.…”

Photomodulated voltammetry investigations on the benzyl radical

“…We assume that the stronger solvation of the anion is responsible for the different behaviour of oxidation and reduction potentials in the investigated solvents. The authors of a recent study [27] performed on several cations and neutral radicals in eleven solvents come to a similar conclusion.…”

Synergistic effect of perchlorate ions and acetonitrile medium explored for extension in copper redoximetry

“…The electrochemistry of coordination compounds in non aqueous media [1][2][3][4][5] is of interest in view of varied solubility, chemical stability, diverse coordina tion and electrochemical behavior of the non aqueous solvents [6,7]. With relatively different redox charac teristics of non aqueous systems as compared to aque ous system, transition metal ion redox couples behave differently in non aqueous media [8].…”