Dy single-molecule magnets from ligands incorporating both amine and acylhydrazine Schiff base groups: the centrosymmetric {Dy} displaying dual magnetic relaxation behaviors.

The novel multidentate chelating ligands N'-(2-pyridylmethylidene)-2-(2-pyridylmethylideneamino)benzohydrazide (Hpphz) and N'-(2-salicylmethylidene)-2-(2-salicylmethylideneamino)benzohydrazide (Hsshz), which incorporate both amine and acylhydrazine Schiff base groups, were synthesized and investigated in Dy coordination chemistry. The reactions of Hpphz and Dy(OAc)·4HO have yielded two {Dy} featuring double OAc bridges: [Dy(Haphz)(OAc)(ROH)] [R = Me (1) and Et (2)], where the Hpphz ligands were in situ hydrolyzed into 2-amino-(2-pyridylmethylideneamino)benzohydrazide ions (Haphz). Besides, the reaction between Hsshz and Dy(NO)·6HO afforded a [Dy(sshz)(μ-OH)(μ-O)(MeOH)]·17.5MeOH·2HO cluster (3). This cluster contained two discrete {Dy} cores, each of which consisted of a pair of {Dy} triangular units. All the complexes displayed a single relaxation process of single-molecule magnet (SMM) behaviors under a zero dc field. Both 1 and 2 showed field-induced dual magnetic-relaxation behaviors. However, their diluted samples (1@Y and 2@Y) only showed one-step relaxation behaviors whether under a zero or applied dc field, indicating that the dual magnetic-relaxation behaviors of 1 and 2 were absent after the dilution. Combined with ab initio calculations, it could be infered that the dual magnetic-relaxation behaviors of 1 and 2 might be ascribled to the joint contributions of the single ion anisotropy and magnetic interactions. Examples of this type are rather rare in previous studies. Ab initio calculations also suggested that the discrepancy between the relaxation processes of 1 and 2 may be caused by the small difference between their magnetic interactions.