A series of new octanuclear Ln8 clusters: magnetic studies reveal a significant cryogenic magnetocaloric effect and slow magnetic relaxation

Abstract

The reaction of a new pentadentate Schiff base hydrazide ligand, (E)-methyl N′-(2-hydroxy-3-methoxybenzylidene)hydrazinecarboxylate (HL), with lanthanide nitrate, and sodium acetate in the presence of triethylamine, resulted in a novel family of octanuclear neutral compounds, [Ln₈(μ₃-O)₄(L)₈(CH₃COO)₄(CO₃)₂]·xH₂O, where Ln = Gd (1), Tb (2), Dy (3), or Ho (4). Compounds 1–4 contained two unusual Ln₄ boat-shaped units, which were held by four L⁻ chelating ligands, two μ₃-O²⁻, and one μ₄-CO₃²⁻. These structures were interconnected by four CH₃COO⁻ ions, forming a novel Ln₈ cluster. Magnetic studies revealed antiferromagnetic Gd⋯Gd interactions in Gd₈, which exhibited a significant magnetocaloric effect and a magnetic entropy change as large as 32.49 J K⁻¹ kg⁻¹ at a field of 7 T at 2 K. In addition, Dy₈ exhibited a frequency dependent slow relaxation of magnetization at a zero applied direct current magnetic field.