Cobalt spectroelectrochemistry

On the basis of spectroelectrochemistry it has been proposed that cobalt corrolate is reduced with a mechanism similar to that occurring in the case of cobalt porphyrinates as shown in Fig. 22 where the cyclic voltammograms in the four non-aqueous solvents investigated are also shown. 

Spectroelectrochemistry [Fig. 41(a,h)] measurements showed that the reversible wave at 0.2 V involves two electrochemical processes, corresponding to the Ru (III)Ru(III)Ru(III)/Ru(III)Ru(III)Ru(II) E° = 0.21 V) and Co(III/II)P( ° = 0.07 V) redox pairs. Surprisingly, in the him, there is an inversion in the redox potentials observed in solution (Table IV), so that the peripheral clusters are reduced before the cobalt porphyrin. This fact was ascribed to axial ligand effects, in changing from the acetonitrile solution to the solid-hlm-water interface (170). This is a very important aspect since now the peripheral complexes in the reduced form can act as electron relays enhancing the catalytic activity of the cobalt porphyrin center. 

Nevin WA, Hempstead MR, Liu W, Leznoff CC, Lever ABP (1987) Elecrochemistry and spectroelectrochemistry of mononuclear and binuclear cobalt phthalocyanines. Inorg Chem 26 570-577... 

Alemdar A, Ozkaya AR, Bulut M. Synthesis, spectroscopy, electrochemistry and in situ spectroelectrochemistry of partly halogenated coumarin phthalonitrile and corresponding metal-free, cobalt and zinc phthalocyanines. Polyhedron. 28(17) 3788-3796... 

Cobalt chloride (anhydrous) was obtained from Aesar, L-histidine hydrochloride from Sigma, N-benzyl-L-histidine from Vega, tetraethylene pentamine (tetren) was obtained from Aldrich. Hater was deionized via a Barnstead Nanopure II ion exchange unit. Cells and electrodes for voltammetry were standard Bioanalytical Systems or Pine Instrument controlled by BAS lOOA, BAS-CV27 or Pine Instrument RDE4 potentiostats and instrumentation. Spectroelectrochemistry was accomplished using a standard... 

Figure 7. Effect on pH on the E value for the Co(II)/Co(III) couple of cobalt bisbenzylhistidine. E determinations carried out by spectroelectrochemistry.

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