Synthesis, structures and magnetism of a series of dinuclear and one-dimensional Ni–Ln complexes: single-molecule magnetic behavior in one-dimensional nitrate-bridged Dy analogue

Abstract

By diffusion of methyl tert-butyl ether vapor into an acetonitrile solution containing [Ni(L)(H₂O)₂] (L = 1,2-bis(3-methoxy-salicylideneaminooxy)ethane) and Ln(NO₃)₃·6H₂O, three Ni–Ln heterometallic complexes, [Ni(μ-L)(MeCN)₂Ln(NO₃)₃] (Ln = Gd for 1, Tb for 2), and [Ni(μ-L)(MeCN)Dy(NO₃)₂(μ-NO₃)·MeCN]_n (3) were obtained. When the reaction was carried out in methanol/chloroform (2 : 1) containing H₂L, Ni(Ac)₂·4H₂O and Ln(NO₃)₃·6H₂O with diffusion of diethyl ether vapor, two Ni–Ln heterometallic complexes [Ni(μ-L)(CH₃OH)(μ-NO₃)Ln(NO₃)₂] (Ln = Tb for 4, and Dy for 5) were synthesized. The X-ray analyses demonstrated that complexes 1, 2, 4 and 5 display 3d–4f heterodinuclear structures, and that the Ni^II and Ln^III ions are bridged by diphenolato atoms for 1 and 2, and by a syn–syn nitrate group and diphenolato atoms for 4 and 5. Compound 3 is made of a rare anti–anti nitrate- and phenolate-bridged Ni–Dy heterometallic chain. All complexes exhibit a net ferromagnetic interaction between the Ni^II and Ln^III ions. Alternating current susceptibility measurements demonstrated that compound 3 behaved as a single-molecule magnet with an effective energy barrier of 15.8 K under a zero direct current field, however, 5 only displayed slow magnetic relaxation under a 2000 Oe direct current field.