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

Abstract

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.