Syntheses and Characterization of Tetrazolate-Based Lanthanide Compounds and Selective Crystallization Separation of...

Selective crystallization offers new opportunities for separating neodymium and dysprosium, which are considerably important in permanent magnets. Two water-soluble nitrogen-rich tetrazolate-based ligands, dtp^2- (H₂dtp = 2,3-di-1H-tetrazol-5-ylpyrazine) and H₂ibt^- [H₃ibt = 4,5-bis(tetrazol-5-yl)imidazole], allow the separation of Nd³⁺ and Dy³⁺ through selective crystallization. The reactions of Ln³⁺ with the ligand Na₂(dtp)·2H₂O lead to two distinct phases, Na[Ln(dtp)(H₂O)₈](dtp)·H₂O (Lndtp1; Ln = La-Pr) and [Ln(H₂O)₈](Hdtp)(dtp)·H₂O (Lndtp2; Ln = Nd and Sm-Lu). Three different compound types, [Ln(H₂ibt)₂(H₂O)₆](H₂ibt)·3(H₂O) (Lnibt1; Ln = La or Ce), [Ln(H₂ibt)(H₂O)₇](H₂ibt)₂·4(H₂O) (Lnibt2; Ln = Pr or Nd), and [Ln(Hibt)(H₂ibt)(H₂O)₄]·4+x(H₂O) (Lnibt3; Ln = Sm-Lu), are obtained from reacting Ln³⁺ and Na(H₂ibt)·3(H₂O). Two different phases are observed for Nd(Lnibt2) and Dy(Lnibt3) in the system of H₂ibt^-, which leads to crystallization-based separation of Nd/Dy with a separation factor of 32 ± 0.7, 10 times higher than that of dtp^2-, and a short separation time of 20 s (1 day for dtp^2-). The higher performance of H₂ibt^- compared to that of dtp^2- provides guidance for the rational design of water-soluble tetrazolate-derived ligands for selective crystallization.