Anions Influence the Relaxation Dynamics of Mono-μ3-OH-Capped Triangular Dysprosium Aggregates

A family of four Dy-3 triangular circular helicates, namely, [Dy-3(HL)(3)(mu(3)-OH)(CH3OH)(2)(H2O)(4)]Cl-1.5(OH)(0.5).0.5H(2)O (1), [Dy-3(HL)(3)(mu(3)-OH)(CH3OH)(3)(H2O)(2)Cl]Cl.CH3OH (2), [Dy-3(HL)(3)(mu(3)-OH)(CH3OH)(3)(H2O)(2)(NO3)](NO3) (3), and [Dy-3(HL)(3)(mu(3)-OH)(CH3OH)(4)(ClO4)](ClO4) (4), were assembled by the reaction of a new acylhydrazone ligand H3L [(3-hydroxy)-N'-((8-hydroxyquinolin-2-yl)methylene)picolinohydrazide] with different dysprosium(III) salts. These compounds represent the first examples of mu-Oacylhydrazone-bridged triangular Dy3 SMMs reported to date. Alternating-current magnetic susceptibility measurements revealed that compounds 1 and 2 show typical SMM behavior with the occurrence of multiple relaxation processes, whereas frequency-dependent relaxation signals without chi peaks were observed in 3 and 4 under zero dc field. Such distinct dynamic behaviors are attributed to the different sizes of the terminal coordination solvent/anions (H2O, Cl, NO3, and ClO4 for 1-4, respectively) at the Dy-3 site. Here, similar deviations from the ideal monocapped square-antiprismatic (C-4v) geometry defined by SHAPE software were observed around local Dy centers in 1 and 2, whereas the situation was completely different in 3 and 4 as a result of the presence of relatively large anions in the limited space defined by three intercrossing rigid hydrazone ligands.