Synthesis, electrochemistry and in situ spectroelectrochemistry of a new Co(III) thio Schiff-base complex with N,N′-bis(2-aminothiophenol)-1,4-bis(carboxylidene phenoxy)butane

A new cobalt Schiff-base complex, [Co(L)(OH)(H2O)] (where L = [N,N'-bis(2-aminothiophenol)-1,4-bis(carboxylidene phenoxy)butane), was synthesized and its electrochemical and spectroelectochemical properties were investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and thin-layer spectro-electrochemistry in solutions of dimethyl sulfoxide (DMSO) and dichloromethane (CH2O2). The [Co(L)(OH)(H2O)] complex displays two well-defined reversible reduction processes with the corresponding anodic waves. The half-wave potentials of the first and second reduction processes were displayed at E-1/2 = 0.08 V and E-1/2 = -1.21 V (scan rate: 0.100 Vs(-1)) in DMSO, and E-1/2 = -0.124 V and E-1/2 = -1.32 V (scan rate: 0.100 Vs(-1)) in CH2Cl2. The potentials of the reduction processes in DMSO are shifted toward negative potentials (0.220-0.112 V) compared to those in CH2O2. The electrochemical results are assigned to two one-electron reduction processes; [Co(III)L] + (-)e -> [Co(II)L](-) and [Co(II)L](-) + (-)e -> [Co(I)L](2-). The six-coordination of the complex remains unchanged during the reduction processes and the electron transfer processes were not followed by a chemical reaction upon scan reversal. It was also seen that [Co(L)(OH)(H2O)1 was reduced at a more positive potential than the corresponding salen analogs. The shift and reversibility are apparently related to the high degree of electron delocalization of the [Co(L)(OH)(H2O)] complex, having a N2O2S2 donor set and two additional benzene units. Additionally, in situ spectro-electrochemical measurements support Co(III)/Co(II) and Co(II)/Co(I) reversible reduction processes with the observation of the corresponding spectral changes with the applied potentials E-app = -0.40 and -1.60 V. Application of the spectroelectrochernical results allowed the determination of E-1/2 and n (the number of electrons) from the spectra of the fully oxidized and reduced species in one unified experiment as well. The results obtained by this method are in agreement with those by the CV and DPV methods. (C) 2007 Elsevier Ltd. All rights reserved.