Spectroscopic investigation of the covalence of An(iii) complexes with tetraethylcarboxamidopyridine

In this work, we report a combined NMR spectroscopic and time-resolved laser fluorescence spectroscopic (TRLFS) study of the complexation of N,N,N ',N '-tetraethyl-2,6-carboxamidopyridine (Et-Pic) with Ln(iii) (La, Sm, Eu, and Lu), Y(iii) and An(iii) (Am and Cm). The focal point of this study was the metal-ligand interaction in the [M(Et-Pic)(3)](3+) (M = An and Ln) complexes. The NMR analyses found slight differences between the An(iii)-N and Ln(iii)-N interactions in contrast to the similar properties of the Am(iii)-O and Ln(iii)-O interactions. These results were supported by TRLFS which shows that the 1 : 3 Cm(iii) complex is by one order of magnitude more stable than the respective Eu(iii) complex. Thus, the ligand's selectivity lies in between those of pure N- and O-donor ligands. The selectivity results from a small partial covalent bonding between the An(iii) ions and Et-Pic.