Step-by-Step and Competitive Assembly of Two Dy(III) Single-Molecule Magnets with Their Performance Tuned by Schiff Base Ligands

The assembly process of lanthanide clusters often involves various complex assembly methods. Hence, studying the stepwise assembly mechanism is extremely difficult. In the assembly process of lanthanide clusters, if the in situ reaction or competitive reaction is involved, the reaction intermediates undergo rapid and complex changes, which makes research on the assembly mechanism even more difficult. Herein, 1-methyl-1H-benzo[d]imidazole-2-carbaldehyde (La) and 1-aminonaphthalen-2-ol (Lb) undergo a stepwise assembly reaction with Dy(III) salts under the promotion of a in situ Schiff base reaction to achieve Dy2synthesis. The stepwise assembly mechanism is La+ Lb→ HL1→ Dy1 → Dy2. In the above Dy2formation reaction, Lais changed to 2-hydroxy-3-methoxybenzaldehyde (Lc), and then pyridin-2-ylmethanamine (Ld) is added. We have found that two different Schiff base ligands are formed in situ, and both are coordinated with Dy(III) ions to form a mixed ligand cluster Dy4by competitive and stepwise assembly. The assembly mechanism is Lb+ Lc/Lc+ Ld→ L2/L3→ Dy1′ → Dy2′ → Dy3′ → Dy4′. We have tracked the competitive assembly process driven by the in situ Schiff base reaction in the lanthanide clusters and proposed its competitive assembly mechanism. Magnetic relaxation studies reveal single-molecule magnet behavior under zero external direct-current field with Ueff= 19.6 K and τo= 1.7 × 10–5s for Dy2and Ueff= 10.0 K and τo= 2.6 × 10–5s for Dy4.