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(Si i Pr 3 ) 2 }(Cp R )][Al{OC(CF 3 ) 3 } 4 ] ( 1-Dy , Cp R = Cp ttt , C 5 H 2 t Bu 3 −1,2,4; 2-Dy , Cp R = Cpʹʹʹ, C 5 H 2 (SiMe 3 ) 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–Cpʹʹʹ 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.