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

Two new 3d-4f heterometallic 1D chains of formulae {[Dy2M2L4(NO3)(H2O)(3)][Dy2M2L4(NO3)(CH3COO)-(H2O)(2)]center dot NO3 center dot 12H(2)O center dot 2C(2)H(5)OH}(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.