Axial dysprosium cyclopentadienyl-amide single-molecule magnets with hysteresis up to 92 kelvin

Molecules showing magnetic memory effects at high temperatures could be used in high-density data storage devices. A magnetic hysteresis temperature (T_H) of 100 K has been achieved for a near-linear dysprosium bis(amide)-alkene single-molecule magnet (SMM), and a bent dysprosium cyclopentadienyl-amide SMM has shown T_H = 73 K. However, both these complexes exhibit fast magnetic relaxation at lower temperatures compared to dysprosium bis(cyclopentadienyl) SMMs. Here we report the synthesis of two highly axial dysprosium cyclopentadienyl-amide SMMs, [Dy{N(SiⁱPr₃)₂}(Cp^R)][Al{OC(CF₃)₃}₄] (1-Dy, Cp^R = Cp^ttt, C₅H₂^tBu₃-1,2,4; 2-Dy, Cp^R = Cp''', C₅H₂(SiMe₃)₃-1,2,4). We find T_H = 91 K for 1-Dy and 92 K for 2-Dy; ab initio calculations on 1-Dy show that magnetic relaxation is controlled by a combination of short dysprosium-ligand distances, a near-linear N-Dy-Cp'''_centroid angle, and constrained vibrational modes. Together, this work demonstrates that dysprosium SMMs with large T_H values can be achieved with a judicious combination of π-aromatic and σ-donor ligands.