Enhancing Steric Hindrance via Ligand Design in Dysprosium Complexes: From Induced Slow Relaxation to Zero-Field Single-Molecule Magnet Properties.

The synthesis and magnetic characterization of three novel Dy compounds, [Dy{PPh2S(NtBu)2}2(μ-Cl2)Li(THF)2] (1), [Dy{PhS(NtBu)2}2(μ-Cl2)Li(THF)2] (2), and [Dy{MeS(NtBu)3}2(μ-Cl2)Li(THF)2] (3), based on the sulfur-nitrogen ligands RS(NtBu)x- (where R = PPh2, x = 2 for (1); R = Ph, x = 2 for (2); and R = Me, x = 3 for (3)) are reported. They represent rare examples of lanthanide-based complexes containing sulfur-nitrogen ligands, whose suitability to enhance the magnetic anisotropy in 3d metals was only recently established. Changes in the ligand field environment drastically affect the magnetic properties, with compounds 1 and 2 displaying field-induced single-molecule magnet (SMM) behavior, while compound 3 shows slow relaxation at zero field. These trends strongly suggest that ligand engineering strategies toward linear dysprosium complexes, similar to those for dysprosocenium complexes, should enhance the SMM performances of SN-based lanthanide compounds.