Structures, magnetic refrigeration and single molecule-magnet behavior of five rhombus-shaped tetranuclear Ln(iii)-based clusters

Abstract

A series of coplanar tetranuclear Ln(III)-based clusters, namely [Ln₄(acac)₄(L)₆(μ₃-OH)₂]·[solvent] (Ln = Eu (1), Gd (2), Tb (3), Dy (4) and Er (5)), have been synthesized by using an 8-hydroxyquinoline Schiff base ligand (HL = 5-(2-thenylidene)-8-hydroxylquinoline) and acetylacetone. Their structures and magnetic properties have been completely characterized. The structure determination shows that clusters 1–5 are isostructural with a rhombus-shaped Ln₄ core. The magnetic studies reveal that the Gd₄ cluster (2) displays cryogenic magnetocaloric effects with a maximum −ΔS_m value of 22.09 J kg⁻¹ K⁻¹ at 2.5 K and ΔH = 7.0 T; while ac susceptibility measurements show that single molecule-magnet behavior is exhibited by the Dy₄ cluster (4) with the anisotropic barrier (ΔE/k_B) of 75.01 K. Interestingly, more than one maximal out-of-phase ac signals (χ′′) were observed in 4, suggesting the operation of multiple magnetic relaxation processes in 4. In addition, the solid state luminescence properties reveal that clusters 1, 3, and 4 display the characteristic lanthanum luminescence at room temperature.