An insight into the complexation of trivalent americium vis-a-vis lanthanides with bis(1,2,4-triazinyl)bipyridine derivatives

Complexation of Am³⁺ and Ln³⁺ (La³⁺, Eu³⁺, and Er³⁺) with two bis(1,2,4-triazinyl)bipyridine (C₂BTBP, C₅BTBP) derivatives has been studied in acetonitrile medium with use of various experimental techniques such as electrospray ionization mass spectrometry (ESI-MS), time-resolved fluorescence spectroscopy (TRFS), UV/Vis spectrophotometry, and solution calorimetry. Metal-ligand stoichiometries and conditional stability constants of these complexes were determined. To the best of our knowledge, this is the first report on the complexation of Am³⁺ with any of the BTBP derivatives with use of UV/Vis spectrophotometric titration to determine the conditional stability constants. Density functional theory (DFT) calculations are carried out on the An³⁺ (U³⁺ and Am³⁺) and Ln³⁺ (La³⁺, Nd³⁺, Eu³⁺, Er³⁺, and Lu³⁺) complexes of BTBP in order to understand the difference between the bonding in actinide and lanthanide complexes. The results indicate a stronger covalent interaction in the An-N bonds as compared to the Ln-N bonds, which leads to an actinide selectivity of this class of ligands. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)