Two Series of Tetranuclear Ln(III)-Based Clusters: Structures, Magnetic Behaviors, and Efficient Cycloaddition of CO2 to Oxazolidinones

Abstract

Four new and interesting Ln₄ clusters formulated as [Ln₄(NO₃)₂(acac)₄(HL1)₂(CH₃OH)₂]·2(CH₃CN)] (Ln = Gd(1), Dy(2); H₄L1 = 2-(hydroxymethyl)-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)propane-1,3-diol); acac = acetylacetone) and [Ln₄(NO₃)₂(acac)₄(L2)₂(CH₃CH₂OH)₂] (Ln = Gd(3), Dy(4); H₃L2 = 2-(((2-hydroxynaphthalen-1-yl)methylene)amino)-2-methylpropane-1,3-diol; acac = acetylacetone) were designed and constructed. Single-crystal X-ray studies indicate that all clusters have a defect dicubane topology in which four Ln(III) are on a plane bond with an arrangement of a parallelogram with the μ₃-O bridge. The difference between the two series of clusters lies in the change of the ligand substituent and terminal coordinated solvent molecules. All Ln(III)-based clusters 1–4 have exhibited excellent solvent stability. The magnetic investigation suggests that clusters 1 and 3 possess a different magnetothermal effect (−ΔS_m = 35.24 J kg^–1 K^–1 for 1, and −ΔS_m = 36.68 J kg^–1 K^–1 for 3). In addition, the diversity in the environment of the metal center leads to the distinct dynamic behavior of U_eff/k_B (21.27 K for 2 and 1.96 K for 4) and τ₀ (1.43 × 10^–7 s for 2 and 2.43 × 10^–6 s for 4). More importantly, clusters 1–4 as heterogeneous catalysts can efficiently catalyze the reaction of CO₂ with bromopropylene oxide and aromatic amine to synthesize oxazolidinones under mild conditions. By comparison, clusters 1 and 2 show higher catalytic activity than 3 and 4, in which the Brønsted acidic −OH groups working together with Lewis acid metal sites improve the catalytic activity of Ln(III)-based clusters 1 and 2. To the best of our knowledge, it is the first example of Ln(III)-based clusters that show good magnetic property and high catalytic activity simultaneously by regulating the coordination environment of Ln(III) ions. Our work provided a promising direction for regulating properties of multifunctional polynuclear Ln(III)-based clusters via changing the coordinated environment of the metal center. It also helps inspire the development of polynuclear Ln(III)-based multifunctional materials.