Enhanced energy barriers triggered by magnetic anisotropy modulation <i>via</i> tuning the functional groups on the bridging ligands in Dy₂ single-molecule magnets

Abstract

Two dinuclear dysprosium complexes of formulae [Dy2(L1)2(NO3)2(MeOH)2]·2MeOH (1) and Dy2(L2)2(NO3)2(MeOH)2 (2), (H2L1 = 4-chloro-2-(((2-hydroxy-3-methoxybenzyl)imino)methyl)phenol, H2L2 = 2-(((2-hydroxybenzylidene)amino)methyl)-6-methoxyphenol) have been synthesized under solvothermal conditions. The two ligands differ in the substituents at the phenol moieties of the ligands. The purposeful exclusion of the functional group -Cl at the phenol backbone significantly changed the geometries of the metal centers, as evidenced by the X-ray crystallographic analysis. In complex 1, two DyIII ions are in D2d local symmetry, while the DyIII ions of 2 are in D4d local symmetry. Consequently, these two complexes demonstrate distinct magnetic properties. Complexes 1 and 2 both exhibit SMM behavior with energy barriers of 51.97 K for 1 and 87.16 K for 2 under a zero direct-current field. Complete-active-space self-consistent field (CASSCF) calculations were performed on the two Dy2 complexes to rationalize the remarkable observed discrepancy in their magnetic behavior. Theoretical calculations reveal that the angle θ between the magnetic axis and the vector connecting two dysprosium(iii) ions is the vital factor for the energy barriers of SMMs. The smaller θ angle of 2 renders it as an SMM with a higher energy barrier. This work demonstrates that tuning the functional groups on the bridging ligands is an effective strategy in modulating the energy barriers of SMMs.