Thermodynamics and nuclear magnetic resonance studies of lanthanide complexation by ethylenediamine-NN′-diacetate-NN′-di-3-propionate

Abstract The proton NMR spectra of ethylenediamine- NN ′- diacetate- NN ′-di-3-propionate and its complexes with alkaline earth and diamagnetic lanthanide ions are described. Quartet splittings of the methylenic protons of the acetate groups upon complexation with metal ions of high charge density is indicative of long-lived metalnitrogen bonds and short-lived metaloxygen bonds. The observation of two AB quartets for the acetate protons complexed to trivalent ions was attributed to an unsymmetrical distribution of the acetate arms around the central ion. For Mg 2+ complex, the two acetate arms are equivalently disposed and the two quartets collapse into one. For the other alkaline earths, a singlet is observed, indicating that the metalnitrogen bond lifetime is also short. The spectra of the propionate protons are consistent of either an ABCD (LuENDPDA and YENDPDA) or an AA′BB′ (MgENDPDA) spectral pattern. The thermodynamic data support these conclusions and show that substitution of C 2 H 4 CO 2 − groups for CH 2 CO 2 − groups decreases the stability of the complex. This results from weakening of the metalnitrogen interaction due to the expansion of the