Extraction and complexation studies with 2,6-bis(5-( tert -butyl)-1 H -pyrazol-3-yl)pyridine in the presence of 2-bromohexanoic acid.

To improve the understanding of the extraction chemistry of An(iii) and Ln(iii) with N-donor ligands 2,6-bis(5-( tert -butyl)-1 H -pyrazol-3-yl)pyridine (C4-BPP) in the presence of 2-bromohexanoic acid was investigated. Extraction studies showed an excellent separation factor of SF Am(III)/Eu(III) ≈ 200 and SF Am(III)/Nd(III) ≈ 60 in comparison with the structurally similar ligand 2,6-bis(5-neopentyl-1 H -pyrazol-3-yl)pyridine C5-BPP (SF Am(III)/Eu(III) ≈ 100), even though C5-BPP showed significantly higher stability constants. Time-resolved laser fluorescence spectroscopy (TRLFS) studies revealed the formation of the ternary 1 : 1 and 1 : 2 complexes [Eu(C4-BPP) n (2-bromohexanoate) m ] (3- m )+ ( n = 1-2) ( and ). [Eu(C4-BPP) 2 (2-bromohexanoate) m ] (3- m )+ was the relevant complex species in solvent extraction. In contrast, Cm(iii) form stable 1 : 3 complexes. The ability of 2-bromohexanoic acid to replace C4-BPP from the inner coordination sphere of Eu(iii) but not from Cm(iii) is due to a more favorable complexation of Cm(iii) over Eu(iii) with C4-BPP. This resulted in a notably more efficient separation of An(iii) and Ln(iii) in comparison with C5-BPP.