Two 3d–4f double helical chains including [Dy2M2]n (M = NiII and CoII) cores exhibiting slow magnetic relaxation

Abstract

Two new 3d–4f heterometallic 1D chains of formulae {[Dy₂M₂L₄(NO₃)(H₂O)₃][Dy₂M₂L₄(NO₃)(CH₃COO)(H₂O)₂]·NO₃·12H₂O·2C₂H₅OH}_n [M = Ni (1); Co (2)] have been prepared using the multidentate ligand 2-{[(2-hydroxy-3-methoxyphenyl)methylidene]amino}benzoic acid (H₂L), which has NO and OO′ chelating pockets that are able to selectively encapsulate Ln^III and transition metal ions, respectively. Crystal structure analyses reveal that the two complexes are isostructural and display one-dimensional ladder-like double helical chain structures, in which the two single helical chains {[Dy₂M₂L₄(NO₃)(H₂O)₃]⁺} and {Dy₂M₂L₄(NO₃)(CH₃COO)(H₂O)₂} (M = Ni(1), Co(2)) both run along the c-axis and have opposite chirality. Complexes 1 and 2 represent the first example of 3d–4f double-chain frameworks in which the compositions of the two individual chains are different. Variable temperature dc magnetic susceptibility studies reveal different strengths of ferromagnetic interactions between the magnetic centers in 1 and 2, which is mainly attributed to the different metal centers and finally results in the distinctive magnetic dynamic behaviors.