The effect of co-ligands on the performance of single-molecule magnet behaviours in a family of linear trinuclear Zn–Dy–Zn complexes with a compartmental Schiff base

Abstract

We present herein magneto-structural studies of three heterometallic Zn₂Dy complexes: [Zn₂Dy(L)₂Cl₂(H₂O)](ClO₄)·4H₂O (1), [Zn₂Dy(L)₂Br₂(H₂O)](ClO₄)·4H₂O (2) and [Zn₂Dy(L)₂(OAc)I(H₂O)]I₃·4H₂O (3), utilizing a new Schiff base ligand, N,N’-bis(3-methoxy-5-methylsalicylidene)-1,2-diaminocyclohexane (H₂L). Complexes 1 and 2 exhibit remarkable magnetic relaxation behaviour with relatively high energy barriers in zero field (U_eff: 244 K for 1 and 211 K for 2) and notable hysteresis temperatures, despite the low local geometric symmetry around the central Dy^III ions. The SMM performance of these complexes is further enhanced under an applied magnetic field, with U_eff increasing to 309 K for 1 and 269 K for 2, positioning them as elite members within the Zn–Dy SMM family. These findings emphasize the substantial influence of remote modulation on Zn^II beyond the first coordination sphere of Dy^III ions on their dynamic magnetic relaxation properties. Ab initio studies demonstrate that the relative orientation of the phenoxo-oxygen donor atoms around the Dy^III ion is critical for determining the magnetic anisotropy and relaxation dynamics in these systems. Additionally, experimental and theoretical investigations reveal that the coordination of the bridging acetate towards the hard plane, combined with significant distortion from the ideal ZnO₂Dy diamond core arrangement caused by the acetate ion, results in low magnetic anisotropy in complex 3, thereby leading to field-induced SMM behaviour. Overall, this study unveils the effects of co-ligands on the SMM performance in a series of linear trinuclear Zn–Dy–Zn complexes, which exhibit low local geometric symmetry around the Dy^III centres.