Octanuclear Ln(III)-Based Clusters Assembled by a Polydentate Schiff Base Ligand and a β-Diketone Co-Ligand: Efficient Conversion of CO₂ to Cyclic Carbonates and Large Magnetocaloric Effect

Abstract

A series of new Ln8 clusters [Ln8(acac)4(HL)4(L)2(μ3-O)4(C2H5O)4]·2C2H5OH·2CH2Cl2 (Ln(III) = Gd (1), Dy (2), and Ho (3); Hacac = acetylacetone and H2L = 2-hydroxy-benzoic acid (5-hydroxymethyl-furan-2-ylmethylene)-hydrazide) have been designed and constructed using a multiple coordination site Schiff base ligand (H2L) as well as a β-diketonate auxiliary ligand. The structures, magnetic properties, and catalytic performance of clusters 1–3 have been studied. X-ray crystallography data revealed that clusters 1–3 possess similar structures with two chair-form Ln4 cores bridged by four μ3-O atoms. Clusters 1–3 display extensive and high solvent stability. Magnetic analysis exhibits that cluster 1 possesses a comparably large magnetocaloric effect (−ΔSm = 33.06 J kg–1 K–1 at 2.0 K and 7.0 T). AC susceptibility measurement suggests that cluster 2 exhibits single-molecule magnet behavior under zero-field conditions. What’s more, all clusters can effectively convert CO2 with epoxides. The highest yield is 98% at 70 °C 0.1 MPa catalyzed by 1. In addition, cluster 1 can be reused three times with a negligible loss of catalytic activity.