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

A family of four Dy3 triangular circular helicates, namely, [Dy3(HL)3(μ3-OH)­(CH3OH)2(H2O)4]­Cl1.5(OH)0.5·0.5H2O (1), [Dy3(HL)3(μ3-OH)­(CH3OH)3(H2O)2Cl]­Cl·CH3OH (2), [Dy3(HL)3(μ3-OH)­(CH3OH)3(H2O)2(NO3)]­(NO3) (3), and [Dy3(HL)3(μ3-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 μ-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 χ″ 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 Dy3 site. Here, similar deviations from the ideal monocapped square-antiprismatic (C4v) 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.