Linear hexanuclear helical dysprosium single-molecule magnets: the effect of axial substitution on magnetic interactions and relaxation dynamics

Abstract

The reaction between the rigid Schiff-base ligand H₄L ([3,6-bis(2-hydroxy-3-methoxybenzylidene)hydrazinecarbonyl]-pyridazine) and different dysprosium(III) salts afforded two new linear hexanuclear helical clusters, [Dy₆L₃(SCN)₆(DMF)₈]·4DMF (1), and [Dy₆L₃(NO₃)₆(DMF)₄(H₂O)₂]·8DMF (2), which possess a similar Dy₆ core with [Dy₆L₃(PhCOO)₆(CH₃OH)₆]·11CH₃OH·H₂O (3). Modulation of the axial ligands around Dy^III sites causes different coordination geometries and magnetic interactions, resulting in distinct magnetic relaxation behaviors. Compounds 1 and 2 show typical single-molecule magnet (SMM) properties with effective barriers (U_eff) of 15 and 68 K, respectively, which could greatly profit from strong ferromagnetic interactions compared with compound 3. Presence of a hula-hoop-like geometry of the Dy^III ions and stronger ferromagnetic interactions results in better SMM performance of compound 2 than that of 1.