Fine-tuning the magnetocaloric effect and SMMs behaviors of coplanar RE4 complexes by β-diketonate coligands
By introducing different β-diketonate coligands 1,3-diphenyl-1,3-propanedione (dbm) and acetylacetonate (acac), two series of new tetranuclear rare earth (RE) complexes [RE4(dbm)4L6(μ3-OH)2]·xCH3CN·yCH2Cl2 (RE = Y (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6) and Lu (7)) and [RE4(acac)4L6(μ3-OH)2]·xCH3CN (RE = Gd (8), Tb (9) and Dy (10)) based on 8-hydroxyquinoline Schiff base have been synthesized and characterized. RE4 clusters display subtle variation in the coordination geometry of REIII ion, but display remarkably dissimilar magnetic behaviors. Magnetic studies show that 2 and 8 act as cryogenic magnetic refrigerants, while 4 and 10 exhibit different slow magnetic relaxation. With the optimized dc fields, two Dy4 clusters both show multiple magnetic relaxation processes by comparing with the zero dc field due to the quantum tunneling of magnetization is mostly suppressed. Interestingly, complex 10 displays two-step relaxation processes occur with Ueff = 37.49 K (FR) and 89.89 K (SR) in the absence of an external field, and one with Ueff = 116.20 K in the presence of a 1500 Oe optimum field. These diversities originate from the substituent group (–C6H5 and –CH3) of β-diketonate coligands in the differences between steric hindrance and electron-donating effect. Additionally, the luminescence properties of 1, 3, 7, and 9 were investigated.