Structure and Magnetism of Ln2III (Ln = Gd, Tb, Dy, and Ho) Assemblies Constructed from a Bis(Hydrazone) Compartmental Ligand: Slow Magnetic Relaxation in the Dy2II Analogue

The aim of the paper was to synthesize a series of Ln(2)(III) (Ln = Gd, Tb, Dy, and Ho) complexes that offer a great perspective to construct functional magnetic materials. Here, we have ventured a Schiff base ligand by combining 2,6-diformyl-4methylphenol with 2-hydroxy-benzoic acid hydrazide, and the ligand is reacted with Ln(NO3)(3)center dot 6H(2)O (1:1), which affords [Ln(2)(H2L)(3)](NO3)(3) (Ln = Gd, Dy, and Ho) and [Ln(2)(H2L)(3)](NO3)(3)(CH3OH) (Ln = Tb) complexes. Structural analyses illustrate that the four complexes have a stoichiometry of 2:3 (M:L), wherein three phenolic oxygen atoms are simultaneously coordinated with two metal atoms to form Ln(III)-O-phenoxo-Ln(III) bridges. Variable-temperature magnetic susceptibility measurements have been performed in the 2-300 K region for all of the compounds. Magnetic studies indicate that the Dy-2(III) analogue exhibits the slow relaxation of magnetization behavior under 700 Oe external dc field with an energy barrier of 2.97-7.73 K. The alternating current (ac) magnetic susceptibility measurements were also performed on the 90:10 (Y:Dy) diluted sample analogue and they depicted that the slow magnetic relaxation properties originated mostly from the single ion but not the coupling between Dy-III ions. The best-fitting results provided U-eff values of 1.61-2.90 K with tau(0) values of 1.31 x 10(-5)-6.97 x 10(-4) s for the diluted sample of Dy-III under 500 Oe dc field.