Slow magnetic relaxation in Ni-Ln (Ln = Ce, Gd, Dy) dinuclear complexes

Three new isomorphous complexes [Ni(o-van-en)LnCl₃(H₂O)] [H₂(o-van-en) = N,N'-ethylene-bis(3-methoxysalicylaldiminate; Ln = Ce (1), Gd (2), Dy (3)] were prepared by a stepwise reaction using mild conditions and were structurally characterised as dinuclear molecules in which Ni and Ln are coordinated by the compartmental Schiff base ligand (o-van-en)⁼ and doubly bridged by O atoms. While the nickel(ii) centre is diamagnetic within the N₂O₂ square-planar coordination of the Schiff base ligand, the lanthanide atoms are octa-coordinated to give an {LnCl₃O₅} chromophore with a fac-arrangement of the chlorido ligands. AC magnetic measurements revealed that all three complexes, including the nominally isotropic Gd(iii) system, show field induced slow magnetic relaxation with two or three relaxation channels: at T = 1.9 K the low-frequency relaxation time is τ_LF(1) = 0.060 s at B_DC = 0.5 T, τ_LF(2) = 0.37 s at B_DC = 0.3 T, and τ_LF(3) = 1.29 s at B_DC = 0.15 T.