Direct NMR Spectroscopic Observation of a Lanthanide-Coordinated Water Molecule whose exchange Rate Is Dependent on the Conformation of the Complexes

A large difference in the exchange rate of the coordinated water molecule is seen in solution for the diastereoisomers M and m of a europium(III) complex with an octadentate, neutral macrocyclic ligand (k(ex)(M) < k(ex)(m)). This finding is of high relevance to the design of more efficient contrast agents for magnetic resonance imaging.