Nuclear Magnetic Resonance Spectroscopy. Nitrogen-15 and Carbon-13 Spectra of Complexes of Ethylenediaminetetraacetic Acid (EDTA) with Closed-Shell Metal Ions

Abstract

The ^(15)N and ^(13)C chemical shift changes have been determined for ethylenediaminetetraacetic acid (EDTA) as the result of changes in pH and complex formation with closed-shell metal ions. The carboxyl-carbon lac shifts in parts per million resulting from complex formation with metal ions are generally smaller than the concomitant shifts of the ^(15)N resonances which themselves are not large. The comparatively small ^(15)N chemical shift changes of EDTA upon metal complex formation are probably due to near-cancellation of variations in local paramagnetic and diamagnetic shielding terms. This may be a general phenomenon for ligands lacking a large local paramagnetic contribution to the shielding of the nitrogen donor atoms.

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