Enhancing Magnetic Relaxation of Dy‐Radical Networks by Tuning the Ligand Field and Magnetic Interactions

A series of two-dimensional Ln-nitronyl nitroxide radical coordination networks, namely, {[Ln(hfac)₃]₃(NITBzald)₂}_n (Ln = Gd 1 and Dy 2; NITBzald = 2-(4-benzaldehyde)-4,4,5,5-tetramethylimidazoline-l-oxyl-3oxide; hfac = hexafluoroacetylacetone) and {[Dy(tfa)₃]₃(NIT-4Py)₂}_n (3; tfa = trifluoroacetylacetonato; NIT-4Py = 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) were synthesized. These complexes are composed of five-spin magnetic building blocks ([Ln₃(NIT)₂]) formed by three Ln^III ions bridged by two NIT units which are extended into 2D structure via coordinated aldehyde or pyridine groups of the radicals. DC magnetic investigations indicate that ferromagnetic Dy-NO interactions dominate in complex 3 whereas antiferromagnetic couplings in complex 2 are predominant. AC magnetic susceptibility studies show that complex 2 just exhibits the onset of slow relaxation of the magnetization while complex 3 presents visible maxima of temperature/frequency-dependent χ″ signals under a zero dc field, evidencing SMM behavior. The observed distinct magnetic relaxation performances of two Dy derivatives could be ascribed to synergistic effect of the different ligand fields of Dy^III ions mainly arising from the distinct coligands (hfac vs. tfa) as well as magnetic exchanges.