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

Abstract

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 (L a ) and 1-aminonaphthalen-2-ol (L b ) undergo a stepwise assembly reaction with Dy(III) salts under the promotion of a in situ Schiff base reaction to achieve Dy2 synthesis. The stepwise assembly mechanism is L a + L b → HL 1 → Dy1 → Dy2. In the above Dy2 formation reaction, L a is changed to 2-hydroxy-3-methoxybenzaldehyde (L c ), and then pyridin-2-ylmethanamine (L d ) 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 Dy4 by competitive and stepwise assembly. The assembly mechanism is L b + L c /L c + L d → L 2 /L 3 → 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 U eff = 19.6 K and τ o = 1.7 × 10 −5 s for Dy2 and U eff = 10.0 K and τ o = 2.6 × 10 −5 s for Dy4.

Assembly of Dy60 and Dy30 cage-shaped nanoclusters

“…Although complex, progress has been made in polyoxometalates [22][23][24][25]36,37 , coordination supramolecular systems 38,39 , coordination molecular cages 26,[40][41][42][43][44][45] , 3d metal-ion clusters [30][31][32][33] , and so on 46,47 . Highvalence Ln(III) ions usually have complex coordination configurations, rich and diverse coordination modes, and coordination balls that are prone to distortion 20,21,[48][49][50] . Such drawbacks lead to the formation of several types of assembly methods in the synthesis of high-nuclearity lanthanide clusters, such as multitemplate induction and stepwise assembly 20,21,[48][49][50] .…”

“…Highvalence Ln(III) ions usually have complex coordination configurations, rich and diverse coordination modes, and coordination balls that are prone to distortion 20,21,[48][49][50] . Such drawbacks lead to the formation of several types of assembly methods in the synthesis of high-nuclearity lanthanide clusters, such as multitemplate induction and stepwise assembly 20,21,[48][49][50] . Given that various assembly methods exist, the formation process of highnuclearity lanthanide clusters is confusing and exploring the assembly mechanism is difficult 20,21,[48][49][50] .…”

“…Such drawbacks lead to the formation of several types of assembly methods in the synthesis of high-nuclearity lanthanide clusters, such as multitemplate induction and stepwise assembly 20,21,[48][49][50] . Given that various assembly methods exist, the formation process of highnuclearity lanthanide clusters is confusing and exploring the assembly mechanism is difficult 20,21,[48][49][50] . Therefore, studies on the assembly mechanism of lanthanide clusters are limited 20,21,[48][49][50][51] .…”

“…Given that various assembly methods exist, the formation process of highnuclearity lanthanide clusters is confusing and exploring the assembly mechanism is difficult 20,21,[48][49][50] . Therefore, studies on the assembly mechanism of lanthanide clusters are limited 20,21,[48][49][50][51] . In 2018, Long and colleagues 51 used high-resolution electrospray ionization mass spectrometry (HRESI-MS) to guide the assembly and synthesis of the wheel-like Eu 24 Ti 8 cluster.…”

“…The relationship between stepwise and template assembly in the formation of high-nuclearity lanthanide clusters was described 48 . Finally, we tracked the competitive assembly process of mixed ligands and in-situ Schiff base replacement in the formation of lanthanide clusters via HRESI-MS 49,50 .…”