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

tridentate ligand LH3 (C11H13N3O4) comprising o-vanillin, hydrazone and oxime donor groups has been employed to prepare a new class of di-and tetranuclear LnIII complexes. The reaction of LH3 with Ln(NO3)(3)center dot xH(2)O in the presence of a suitable base yields the dinuclear Dy-III complex [Dy-2(LH2)(4)(CH3OH)][NO3](2) (1) and the tetranuclear complexes [Dy-4(LH)(4)(LH2)(2)(OH)(2)]center dot 2H(2)O (2) and [Gd-4(LH)(4)(LH2)(2)(OMe)(2)]center dot nH(2)O, (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 GdIII 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 / kB = 26.7 K) and Raman relaxation processes.