Aminopolycarboxylates of rare earths

Potentiometric examination with a fluoride-selective electrode of the Ln(edta)- -F- systems indicate that mixed ligand complexes with composition Ln(edta)F2-and Ln(edta)F23- are formed. The stability constants K1 increase with the atomic number up to Dy, and subsequently decrease. The stability constants K2 are small, their values being around 3 throughout the entire series. A 1H NMR spectroscopic study of the complexes of the diamagnetic elements showed that the methylene and ethylene protons are shifted in the direction of higher fields, which indicates an increase of the Ln3+-donor atom distances. The enthalpy changes connected with the formation of the complexes Ln(edta)F2- are essentially more exothermic than those found for the formation of the complexes LnF2+. (author)