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

Abstract

Four new and interesting Ln 4 clusters formulated as [Ln 4 (NO 3 ) 2 (acac) 4 (HL1) 2 (CH 3 OH) 2 ]·2(CH 3 CN)] (Ln = Gd( 1 ), Dy( 2 ); H 4 L1 = 2-(hydroxymethyl)-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)propane-1,3-diol); acac = acetylacetone) and [Ln 4 (NO 3 ) 2 (acac) 4 (L2) 2 (CH 3 CH 2 OH) 2 ] (Ln = Gd( 3 ), Dy( 4 ); H 3 L2 = 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 μ 3 -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 (−Δ S m = 35.24 J kg –1 K –1 for 1, and −Δ S 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 τ 0 (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 CO 2 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.

Topics & Concepts