Nuclear magnetic resonance studies of neutral lanthanide(III) complexes with tetraaza-macrocyclic ligands containing three phosphinate and one carboxamide co-ordinating arms

Abstract

Novel, neutral EuIII, GdIII and YbIII 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 1H, 13C and 31P NMR spectra of the EuIII and YbIII complexes. Partial assignment of 1H and 13C resonances was possible for one EuIII 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 31P resonances has provided a route to the determination of the Yb–P distances. The addition of the chiral solvating agent β-cyclodextrin to a solution of the YbIII complex containing benzylic substituents on the amido nitrogen allowed the chiral resolution of an enantiomeric pair by 31P NMR spectroscopy. The measurement of water proton longitudinal relaxation rates of solutions of the GdIII complexes indicated that these chelates have one inner-sphere co-ordinated water molecule whereas the parent tetraphosphinate complexes have none.