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

A magnetic hysteresis temperature (<i>T</i>_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 <i>T</i>_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] (<b>1-Dy</b>, Cp^R = Cp^ttt, C₅H₂^tBu₃-1,2,4; <b>2-Dy</b>, Cp^R = Cpʹʹʹ, C₅H₂(SiMe₃)₃-1,2,4). We find <i>T</i>_H = 91 K for <b>1-Dy</b> and 92 K for <b>2-Dy</b>; <i>ab initio</i> calculations on <b>1-Dy</b> 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.