Fine-tuning the magnetocaloric effect and SMMs behaviors of coplanar RE4 complexes by β-diketonate coligands

Abstract

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 RE^III 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 U_eff = 37.49 K (FR) and 89.89 K (SR) in the absence of an external field, and one with U_eff = 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.