Elucidation of the two-step relaxation processes of a tetranuclear dysprosium molecular nanomagnet through magnetic dilution.

A new centrosymmetric tetranuclear aggregate [Dy4(L)2(OAc)8(CH3OH)2] (1) was assembled using a unique symmetrical Schiff base ligand 1,5-bis(salicylidene)-carbohydrazide (H2L). Magnetic studies reveal ferromagnetic interactions between dysprosium ions and two obvious relaxation processes under zero dc field with effective energy barriers Ueff of 38 K and 223 K, the highest among the reported tetranuclear dysprosium molecular nanomagnets. To obtain further evidence on the origination of the slow magnetic relaxation, a diamagnetic yttrium analogue [Y4(L)2(OAc)8(CH3OH)2] (2) and a diluted sample [(Dy0.06Y0.94)4(L)2(OAc)8(CH3OH)2] (3) were synthesized. Further magnetic studies on the diluted sample combined with theoretical calculations indicate that the two-step magnetic relaxation processes in complex 1 originate from the single-ion magnetic behaviors of dysprosium ions with different coordination environments.