A Raman spectroscopic study of the mono- and di-protonated ethylenediaminetetra-acetate ions

Abstract

Raman spectra of aqueous solutions of Na⁺ and ethylenediaminetetra-acetate (edta) at pH 4.5–13 have been obtained together with those of a number of related solid complexes of edta. Analysis of the data suggests that the Hedta^3– ion adopts a configuration, at pH 7.5 in water, in which both nitrogens are equally protonated and hydrogen bonds are formed to two carboxylate groups. The configuration of the H₂edta^2– ion is probably similar, but involves hydrogen bonds to four carboxylate groups.