Single molecule magnet behavior and magnetic refrigeration of four tetranuclear lanthanide (Ln = GdIII, TbIII, DyIII) clusters

Abstract

Four tetranuclear lanthanide clusters: {[Gd₄(L₁)₆(tmhd)₄(μ₃-OH)₂]·2CH₃CN} (1), {[Tb₄(L₁)₆(tmhd)₄(μ₃-OH)₂]·4CH₃CN} (2), {[Dy₄(L₁)₆(tmhd)₄(μ₃-OH)₂]·CH₃CN} (3) and {[Gd₄(L₂)₆(tmhd)₄(μ₃-OH)₂]·8CH₃CN·2CH₂Cl₂} (4) were fabricated by employing two Schiff based ligands (HL₁ = 5-((4-ethylbenzylidene)amino)quinolin-8-ol and HL₂ = 5-(([1,1′-biphenyl]-4-ylmethylene)amino)quinolin-8-ol). Interestingly, the cores of compounds 1–4 are nearly structurally identical. The core of the compounds contains a tetranuclear arrangement of Ln^III ions, which is held together by two pyramidal μ₃-OH⁻ ions and six μ₂ phenol hydroxyl oxygen atoms derived from six ligands. Magnetic studies indicated that 1 and 4 exhibit a cryogenic magnetic refrigeration property (maximum −ΔS_m = 18.02 J K⁻¹ kg⁻¹ for 1, and 15.47 J K⁻¹ kg⁻¹ for 4, ΔH = 7 T at 2.0 K), whereas compound 3 exhibits a slow relaxation of magnetization with an energy barrier (U_eff/k_B) of 83.1 K and τ₀ = 4.18 × 10⁻⁸ s.