Copper(II) Complexes of Ethylenediaminemonoacetic Acid (EDMA). A Polarographic Study of the Solution Equilibria between the Copper(II) Ion and EDMA and the Preparation of Copper(II)-EDMA Complexes

Abstract

In the present paper, the solution equilibria between the copper(II) ion and ethylenediaminemonoacetic acid (EDMA) were determined polarographically and, then copper(II)-EDMA complexes were prepared and characterized using ion-exchange chromatography and the visible and infrared absorption spectra. Since copper(II) ions in an EDMA solution behave reversibly in a polarographic electrolysis, the composition and the stability constants of copper(II)-EDMA complexes were determined from the dependence of the half-wave potential on the concentration of uncomplexed EDMA by employing a modification of the Deford-Hume method. The copper (II) ion was found to form complexes of 1-to-1 and 1-to-2 compositions with EDMA. Their successive formation constants, K₁ and K₂, were 2.5₂×10¹³ and 1.10×10⁸ respectively. The copper(II)-EDMA complex with a 1-to-1 composition was easily isolated from an aqueous solution of pH 3.0–4.0. On the other hand, the complex with a 1-to-2 composition could be isolated in a low yield by adding ethanol from a solution containing an excess amount of EDMA in the pH range from 10.0 to 11.0. From the infrared spectra and the ion-exchange chromatographic behavior, the ethylenediaminemonoacetate ion in the complexes was concluded to function as a tridentate ligand.