The voltammetric study of some phenanthroline-type complexes and of ferrocene with a platinum rotating disk electrode in acetonitrile

Abstract

A platinum rotating disk electrode (RDE) was used for the detailed voltammetric study of complexes: Fe(2,2′-dipyridyl) 3 (ClO 4 ) 2 , Fe(1,10-phenanthroline) 3 -(ClO 4 ) 2 , Fe(cyclopentadienyl) 2 (ferrocene), and Co(2,2′-dipyridyl) 3 (ClO(in4) 3 in acetonitrile (AN) solutions of 0.1 M NaClO 4 . All the complexes react reversibly at the platinum RDE in AN. From the dependence of the half-wave potentials of the waves of these complexes on the ionic strength it was concluded that the complex ions do not associate in their solutions. The values of the standard potentials in AN ( versus the standard hydrogen electrode in water) of the systems tris(dipy)Fe(II) and −Fe(III) (1.103 V), tris(phen)Fe(II) and −Fe(III) (1.119 V), bis(cpdien)Fe(II) and −Fe(III) (0.373 V), and tris(dipy)Co(II) and −Co(III)(0.339 V) were calculated from the haft-wave potential values. The values of the diffusion coefficients at 25°C and the Stokes' Law radii were determined for tris(dipy)Fe(II) (1.10×10 −5 cm 2 s −1 ; 5.27 Å), tris(phen)Fe(II) (1.08 × 10 −5 cm 2 s −1 ; 5.42 Å), bis (cpdien)Fe(II) (2.49 × 10 −5 , cm 2 s −1 ; 2.38 Å), and tris(dipy)Co(III) (0.98×10 −5 cm 2 s −1 ; 5.22 Å) in an acetonitrile solution of 0.1 M NaClO 4 . The relative error of the diffusion coefficient determination was 2–3%.