Proton resonance spectra of some cobalt (II) complexes in aqueous solutions

Abstract

Proton resonance spectra have been measured for the Co(II) complexes of some aminopolycarboxylate ligands (iminodiacetate and its C-methyl, N-methyl, N-ethyl and N-2-hydroxyethyl derivatives; imino di-β-propionate; imino β-propionate acetate and two of its C-methyl derivatives and nitrilo β-propionate diacetate). The lines occur generally at higher fields than those of the corresponding protons in the Ni(II) complexes, and it is suggested that in addition to the contact interaction, there is a pseudo-contact contribution to the shifts in the Co(II) complexes. An approximate calculation of this effect is made. The spectra indicate the presence of spatial isomers with some complexes, and the ligands N-2-hydroxyethyl iminodiacetate and nitrilo β-propionate diacetate, which form three chelate rings in the 1 : 1 complexes, are shown to be tridentate in the 2 : 1 complexes.