Fractional sublimation of the β-diketone chelates of the lanthanide and related elements

Abstract

Various β-diketone chelates of Sc(III), Y(III), Th(IV), U(IV). U(VI), Zr(IV) and the lanthanides have been prepared, characterized and investigated to determine if they were volatile and stable. The ligands employed were acetylacetone(AA), trifluoroacetylacetone(TFAA), hexafluoroacetylacetone(HFAA), and dipivaloyl-methane(DPM). The chelates were sublimed in a fractional vacuum sublimator and the recrystallization temperature zones recorded for individual chelates. None of the lanthanide acetylacetonates arc volatile but the Sc(III), Th(IV), U(IV) and dioxouranium(VI) acetylacetonates are thermally stable and quite volatile below 150° at 1 mm mercury pressure. The lanthanide, Sc(III), Y(III), and dioxouranium(VI) trifluoroacetylacetonates are volatile and can be vacuum-sublimed below 150°, but are thermally unstable; only the Th(IV) chelate is sufficiently stable to be quantitatively recovered by sublimation. The Sc(III), Y(III), Th(IV), and lanthanide hexafluoroacetylacetonates are thermally stable and easily sublimed below 125° in vacua or at atmospheric pressure. All the dipivaloylmethanates studied were thermally stable and volatile and could be quantitatively recovered by vacuum sublimation below 140°. The volatility of the HFAA and DPM lanthanide chelates increased with an increase in atomic weight (a decrease in ionic radii) of the lanthanides. The lack of volatility observed for the lanthanide AA and TFAA chelates is attributed to the fact that only hydrates of the chelates were formed, which decomposed at elevated temperatures in vacuo to form basic polymeric compounds. Separations are proposed for numerous binary mixtures of the β-diketone chelates of the lanthanide and related elements. Recrystallization temperature zones are given for the following binary mixtures which were quantitatively resolved by the fractional sublimation technique; 118-88° for Nd(DPM) 3 and 84-48° for Tm(DPM) 3; 72-49° for Sc(DPM) and 120-88° for Pr(DPM); 128-79° for La(DPM) 3 and 79-47° for Yb(DPM) 3; 70-47° for Th(TFAA) 4 and 116-96° for Gd(TFAA) 3; 52-42° for Th(HFAA) 4 and 120-80° for La(HFAA) 3.