Isoskeletal {FeIII4Ln} (Ln = Dy, Gd, Y) and {GaIII4Dy} Clusters as Platforms for Probing Lanthanide-Controlled Relaxation Dynamics

A new family of four pentanuclear {M4Ln} (MIII = Fe, Ga) clusters, [FeIII4Ln(OMe)2(O2CMe)(sacb)5(sacbH)(MeOH)2](ClO4) [LnIII = Dy (1), Gd (2); Y (3)] and the analogous complex [GaIII4Dy(OMe)2(NO3)(sacb)6(MeOH)] (4), have been synthesized using the tetradentate Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH2). Single-crystal X-ray diffraction revealed that all compounds possess an unprecedented {MIII4Dy(μ-ΟMe)2(μ-Ο2CR)6}7+ “bat-like” motif. Direct current (dc) magnetic susceptibility measurements showed predominant antiferromagnetic interactions within 1−3, with the {Fe4Y} compound allowing quantitative evaluation of the FeIII···FeIII exchange coupling. In contrast to the {Fe4Dy} cluster, which does not exhibit slow magnetic relaxation, the {Ga4Dy} analogue displays tails of out-of-phase ac signals attributed to a fast-relaxing single-molecule magnet with a small energy barrier for the magnetization reversal. The comparative study highlights the decisive role of the trivalent metal ions (paramagnetic FeIII vs. diamagnetic GaIII) in governing the relaxation dynamics of the DyIII center through modulation of its crystal-field environment. These results further demonstrate the {M4Ln} platform as a valuable model for the development of magnetostructural correlations in 4f-based heterometallic chemistry.