In Situ Approach for Constructing Ln(III)-Based Tetranuclear Compounds: Magnetocaloric Effect, Slow Magnetic Relaxation Behavior, and High-Efficiency Conversion of CO ₂

Four novel Ln 4 clusters [Ln 4 (dbm) 2 (H 2 L 1 ) 2 (HL 2 ) 2 (CH 3 O) 2 ]· x CH 2 Cl 2 · y CH 3 OH· z CH 3 CN (Ln(III) = Gd ( 1 ) ( x = 2, y = 8, z = 0), Dy ( 2 ) ( x = 0, y = 6, z = 0), Ho ( 3 ) ( x = 0, y = 8, z = 4), and Er ( 4 ) ( x = 2, y = 8, z = 0), dbm = 1,3-diphenylpropane-1,3-dione, H 4 L 1 = N ′ 2, N ′ 6 -bis(( E )-3,5-di- tert -butyl-2-hydroxybenzylidene)pyridine-2,6-dicarbohydrazide, and H 3 L 2 = ( E )- N ′-(3,5-di- tert -butyl-2-hydroxybenzylidene)-6-(hydroxymethyl)picolinohydrazide) were synthesized through an in situ solvothermal method and characterized using IR, PXRD, TGA, and single-crystal X-ray diffraction. The magnetic properties of 1–4 and the performance of compound 1 in catalyzing the cycloaddition of CO 2 were studied in detail. While compound 1 shows promising magnetocaloric performance (−Δ S m = 18.11 J kg –1 K –1 ( T = 2.0 K and Δ H = 7.0 T)), compound 2 displays typical SMMs behavior, with the slow relaxation process giving Δ E / k B = 38.86 K and τ 0 = 1.53 × 10 –7 s, and the fast relaxation process giving Δ E / k B = 26.49 K and τ 0 = 1.13 × 10 –6 s. Notably, compound 1 exhibited remarkable substrate generality toward diverse epoxides and maintained excellent recyclability over multiple cycles. This study presents novel compounds that exhibit both magnetism and catalytic performance for CO 2 cycloaddition reactions. Furthermore, it not only represents a significant step forward in the development of multifunctional materials but also provides a promising strategy for the high-value utilization of CO 2 .