Slow magnetic relaxation in Dy2 and Dy4 complexes of a versatile, trifunctional polydentate N,O-ligand

Abstract

A tridentate ligand LH₃ (C₁₁H₁₃N₃O₄) comprising o-vanillin, hydrazone and oxime donor groups has been employed to prepare a new class of di- and tetranuclear Ln^III complexes. The reaction of LH₃ with Ln(NO₃)₃·xH₂O in the presence of a suitable base yields the dinuclear Dy^III complex [Dy₂(LH₂)₄(CH₃OH)][NO₃]₂ (1) and the tetranuclear complexes [Dy₄(LH)₄(LH₂)₂(OH)₂]·2H₂O (2) and [Gd₄(LH)₄(LH₂)₂(OMe)₂]·nH₂O, (3). In these complexes, LH₃ is either monodeprotonated (1) or a mixture of mono- and doubly-deprotonated ligands (2 and 3) binding lanthanide ions via N_diazine, O_hydrazone, and O_vanillin donors, while the remaining vacant coordination sites are occupied by O_MeOH (1), O_hydroxide (2) and methoxides (3). DC magnetic susceptibility studies on the isotropic tetranuclear Gd^III complex (3) reveal weak antiferromagnetic exchange interactions between the Ln^III ions. AC studies reveal that the dinuclear complex (1) exhibits field-induced slow relaxation of magnetization with U_eff = 43.4 K, whereas 2 is a single molecule magnet, exhibiting slow relaxation of magnetization under zero field below 18 K, which is modelled using a combination of Orbach (U_eff/k_B = 26.7 K) and Raman relaxation processes.