SOLVENT EFFECTS IN THE ELECTROREDUCTION OF [DIAMINE-N,N'-POLYCARBOXYLATO]CHROMATE(III) COMPLEXES AT A MERCURY-ELECTRODE

The effect of the solvent on the electroreduction of ethylenediaminetetraacetatochromate(III) ([CrEDTA](-)), cyclohexanediamineletraacetatochromate(III) ([CrCYDTA](-)) and (2-hydroxyethyl)ethylenediaminetriacetato-chromimum(III) ([CrHEDTRA]) has been investigated in different solvents on a mercury electrode using convolution potential sweep voltammetry. The observed electron transfer rate constant and the transfer coefficient have been corrected for double-layer effects. It has been shown that the formal potential for the reduction of all three complexes in a series of solvents is a linear function of the solvent acceptor number. The logarithm of the corrected standard rate constant for the EDTA and CYDTA complexes depends on the solvent acceptor number and the logarithm of the solvent's longitudinal relaxation time, whereas for [CrHEDTRA] it depends on the solvent's acceptor and donor numbers. It is concluded that, in the case of the EDTA and CYDTA complexes, no solvent molecules are incorporated as ligands in the first coordination sphere. However, in the HEDTRA complex the coordinated water molecule originally present is substituted by the solvent in which the reaction takes place.