Four Ln2 compounds constructed by a polydentate Schiff base ligand: Gd2 compound displaying large magnetocaloric effect and Dy2 compound showing single-molecule magnet behavior

Four new acyloxy bridged Ln III 2 compounds [Ln 2 (L) 2 (acac) 2 (EtOH) 2 ] (Ln(III) = Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), and Ho ( 4 ), Hacac = acetylacetone, and H 2 L = pyridine-2-carboxylic acid (3-ethoxy-2-hydroxy-benzylidene)-hydrazide) have been prepared by a polydentate Schiff base ligand under solvothermal condition. The single-crystal X-ray structure study reveals that 1 – 4 are isostructural and contain a parallelogram Ln 2 O 2 core. Magnetic study reveals that antiferromagnetic interaction exists in compound 1 . More importantly, compound 1 displays well cryogenic magnetic refrigeration property (−Δ S m  = 28.2 J kg −1  K −1 , T  = 2.0 K and Δ H  = 70 kOe); while compound 3 exhibits evident single-molecule magnet behavior under zero-field condition (Δ E / k B  = 26.8 K, τ 0  = 1.05 × 10 −7  s).