NUCLEAR-MAGNETIC-RESONANCE STUDIES OF NEUTRAL LANTHANIDE(III) COMPLEXES WITH TETRAAZA-MACROCYCLIC LIGANDS CONTAINING 3 PHOSPHINATE AND ONE CARBOXAMIDE COORDINATING ARMS

Novel, neutral Eu-III, Gd-III and Yb-III complexes have been obtained with tetraaza-macrocyclic ligands containing three phosphinate and one carboxamide co-ordinating arms. The overall results are consistent with a co-ordination geometry based on the octadenticity of these ligands. Among the possible 16 enantiomeric pairs one is largely dominant as ascertained by the high resolution H-1, C-13 and P-31 NMR spectra of the Eu-III and Yb-III complexes. Partial assignment of H-1 and C-13 resonances was possible for one Eu-III complex on the basis of homo- and hetero-correlated two-dimensional NMR experiments. The evaluation of the Curie contribution to the longitudinal relaxation rates of the P-31 resonances has provided a route to the determination of the Yb-P distances. The addition of the chiral solvating agent beta-cyclodextrin to a solution of the Yb-III complex containing benzylic substituents on the amido nitrogen allowed the chiral resolution of an enantiomeric pair by P-31 NMR spectroscopy. The measurement of water proton longitudinal relaxation rates of solutions of the Gd-III complexes indicated that these chelates have one inner-sphere co-ordinated water molecule whereas the parent tetraphosphinate complexes have none.