Chromium(III)-complexes of some aminopolycarboxylic acids and their polarographic behaviour

Abstract

Summary The complexes of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid and triethylenetetraminehexaacetic acid with Cr3+ ions, which are slowly formed in slightly acidic solutions, yield well developed polarographic waves in the potential range around −1.20 V and poorly-developed waves at −1.60 V. If either of the ligands is added to a solution of Cr3+ ions, a wave appears immediately at −1.20 V; the corresponding current is due to the rate of the reaction between the reduced Cr2+ ions and the ligand at the surface of the electrode. The presence of NO3− ions causes increase of the wave of the complexes in the potential range around −1.20 V; this effect is due to the oxidation of the corresponding Cr(II) complexes with NO3− ions at the surface of the electrode. The presence of La3+ ions causes an increase in the height of the waves of the complexes in the potential range around −1.60 V. All the described chromium(III) complexes yield square-wave polarographic peaks at −1.20 V. These peaks are not influenced by the presence of NO3− ions. La3+ ions cause an increase in the square-wave polarographic peaks corresponding to the reduction of the Cr(III)-TTHA complex. This effect is attributed to the formation of the mixed binuclear complex, Cr-La-TTHA, which alters the rate of the electrode process involving the reduction of the Cr(III)-TTHA complex.