Electrochemical Impedance Spectroscopy and Cyclic Voltammetry of cis-[Cr(bipy)(2)(SCN)(2)]I (where bipy: 2,2'-Bipyridine) in Polar Solvents

Cyclic voltammetric studies (CV) on the complex cis-bis(2,2'-bipyridine)bis(thiocyanate)chromium(III) iodide [Cr(bipy)(2)(SCN)(2)]I (where bipy: 2,2'-bipyridine, C10H8N2) were recorded on platinum (Pt) and glassy carbon (GC) electrodes in either acetonitrile (ACN) or acetone (ACE) solvent media including n-tetrabutylammonium hexafluorophosphate (NBu4PF6) as supporting electrolyte, at scan rates (v) ranging from 0.05 to 0.12 Va <...s(-1). In addition, electrochemical impedance spectroscopic (EIS) measurements in the frequency (f) range from 0.1 Hz to 50 kHz were carried out on GC and Pt electrodes. The half-wave potential (E (1/2)) of the redox couple Cr(III)/Cr(II) was determined as -0.84 V and -0.79 V (versus Ag/AgCl) in ACN and ACE, respectively. The heterogeneous electron transfer rate constant (k (s)) corresponding to the couple Cr(III)/Cr(II) was found to be greater on GC compared to the Pt electrode. The nature of the solvent medium also affects the kinetics of the investigated couple, to be exact, k (s) increases remarkably upon replacement of ACE by ACN. The EIS results indicate that the GC electrode is a better capacitor and provides the smaller charge transfer resistance in ACN.