Tuning magnetic exchange and relaxation dynamics in dinuclear Dy( iii ) single-molecule magnets via co-ligand modulation on a hydrazone-based Schiff base platform

calculations reveal that the intramolecular Dy-Dy interaction involves an interplay between a FM dipolar coupling and AFM exchange. In complexes 1 and 2, the AFM interaction dominates the bulk magnetic response while complexes 3 and 4 exhibit a FM curve profile. This interplay has a decisive impact on the single-molecule magnet (SMM) properties. As a consequence, complexes 1 and 2 exhibit only weak, field-induced slow magnetic relaxation due to enhanced quantum tunneling of magnetization, whereas complexes 3 and 4 display clear zero-field SMM behavior with superior relaxation performance. Theoretical analysis further demonstrates that co-ligand-dependent coordination geometries control the orientation of the magnetic easy axes and modulate the effectiveness of magnetic coupling, thereby establishing a direct correlation between the overall magnetic interaction and the observed SMM behavior in this dinuclear Dy(III) family.