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

The reaction between the rigid Schiff-base ligand HL ([3,6-bis(2-hydroxy-3-methoxybenzylidene)hydrazinecarbonyl]-pyridazine) and different dysprosium(iii) salts afforded two new linear hexanuclear helical clusters, [DyL(SCN)(DMF)]·4DMF (1), and [DyL(NO)(DMF)(HO)]·8DMF (2), which possess a similar Dy core with [DyL(PhCOO)(CHOH)]·11CHOH·HO (3). Modulation of the axial ligands around Dy 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) 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 ions and stronger ferromagnetic interactions results in better SMM performance of compound 2 than that of 1.