Lanthanum-139 nuclear magnetic resonance studies of polyaminocarboxylate-lanthanum complexes in aqueous solution

Several complexes of La(III) with aminocarboxylate and polyaminocarboxylate ligands in aqueous solution have been studied using ¹³⁹La chemical-shift and linewidth measurements. The ligand-induced shifts of the ¹³⁹La NMR resonance were found to depend, at least to first order, on additive substituent contributions, and were empirically related to the number and type of coordinated oxygen and nitrogen atoms. A previously proposed relationship between the number of coordinated carboxylate oxygen atoms and observed ¹³⁹La shifts does not seem to hold for the polyaminocarboxylate complexes and we propose a new empirical relationship which allows an accurate prediction of the number and types of ligand donors in these systems. The ¹³⁹La linewidths also provide qualitative information about the symmetry of each La³⁺ chelate. The results show that ¹³⁹La NMR can be a powerful technique for elucidating the structure and dynamics of lanthanide complexes in solution.