An 17O NMR Study of Diamagnetic and Paramagnetic Lanthanide-tris(oxydiacetate) Complexes in Aqueous Solution

¹⁷O-enriched complexes between oxydiacetate ligand and several diamagnetic and paramagnetic lanthanide(III) metal ions (Ln) were investigated by solution-state ¹⁷O NMR spectroscopy. The bound-state signals of chelating (O _in) and nonchelating (O _out) oxygen atoms of the carboxylate groups were observed for all the samples investigated. The data indicate that the ¹⁷O line width is dominated by contributions from both quadrupole relaxation and chemical exchange in the case of Pr and Nd complexes. Dissection of the chemical shift induced by metal ions on O _in into Fermi contact and pseudocontact contributions was performed, and the hyperfine coupling constant (A/ℏ) was estimated. No evidence of structural changes within the series was detected.