Enhancing single-molecule magnet behaviour through decorating terminal ligands in Dy2 compounds

Abstract

The utilization of two isomorphic ligands with different substituents leads to two centrosymmetric Dy^III dimers, namely, [Dy₂(bfbpen)₂(H₂O)₂]·2I⁻ (1) and [Dy₂(bcbpen)₂(H₂O)₂]·2I⁻·0.5H₂O (2) (H₂bfbpen = N,N′-bis-(2-hydroxy-5-fluoro-benzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine and H₂bcbpen = N,N′-bis-(2-hydroxy-5-chloro-benzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine). Although Dy ions in both compounds uniformly exhibit a square-antiprism geometry, the critical difference found in the terminal substituents of the two ligands fine-tunes the local crystal field around Dy centers and the dinuclear molecular structures of 1 and 2. Magnetic investigations unveil that both 1 and 2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behaviour with different energy barriers of 20.9 K for 1 and 72.7 K for 2 under a zero direct-current (dc) field, as well as 26.9 K for 1 under a 1200 Oe dc field. Compared to 1, the stronger uniaxial anisotropy and magnetic exchange in 2 render it a better SMM as evidenced by the higher energy barrier. Ab initio calculations are also performed on both Dy₂ compounds to rationalize the observed discrepancy in their magnetic behaviours. The contribution illustrates that the SMM behaviour could be effectively enhanced by means of deliberate local structural manipulation.