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

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- (H 2 dtp = 2,3-di-1 H -tetrazol-5-ylpyrazine) and H 2 ibt - [H 3 ibt = 4,5-bis(tetrazol-5-yl)imidazole], allow the separation of Nd 3+ and Dy 3+ through selective crystallization. The reactions of Ln 3+ with the ligand Na 2 (dtp)·2H 2 O lead to two distinct phases, Na[Ln(dtp)(H 2 O) 8 ](dtp)·H 2 O ( Lndtp1 ; Ln = La-Pr) and [Ln(H 2 O) 8 ](Hdtp)(dtp)·H 2 O ( Lndtp2 ; Ln = Nd and Sm-Lu). Three different compound types, [Ln(H 2 ibt) 2 (H 2 O) 6 ](H 2 ibt)·3(H 2 O) ( Lnibt1 ; Ln = La or Ce), [Ln(H 2 ibt)(H 2 O) 7 ](H 2 ibt) 2 ·4(H 2 O) ( Lnibt2 ; Ln = Pr or Nd), and [Ln(Hibt)(H 2 ibt)(H 2 O) 4 ]·4+ x (H 2 O) ( Lnibt3 ; Ln = Sm-Lu), are obtained from reacting Ln 3+ and Na(H 2 ibt)·3(H 2 O). Two different phases are observed for Nd( Lnibt2 ) and Dy( Lnibt3 ) in the system of H 2 ibt - , 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 H 2 ibt - compared to that of dtp 2- provides guidance for the rational design of water-soluble tetrazolate-derived ligands for selective crystallization.