Soft magnetic hysteresis in a dysprosium amide-alkene complex up to 100 kelvin

Lanthanides have shown magnetic memory at both the atomic^1,2 and molecular^3,4 level. The magnetic remanence temperatures of lanthanide single-molecule magnets can surpass d-transition metal examples^5,6, and since 2017, energy barriers to magnetic reversal (U_eff) from 1,237(28) cm^-1 to 1,631(25) cm^-1 and open magnetic hysteresis loops between 40 K and 80 K have typically been achieved with axial dysprosium(III) bis(cyclopentadienyl) complexes^7-17. It has been predicted that linear dysprosium(III) compounds could deliver greater m_J (the projection of the total angular momentum, J, on a quantization axis labelled z) state splitting and therefore higher U_eff and hysteresis temperatures^18-21, but as lanthanide bonding is predominantly ionic^22,23, so far dysprosium bis(amide) complexes have shown highly bent geometries that promote fast magnetic reversal^24,25. Here we report a dysprosium bis(amide)-alkene complex, [Dy{N(SiⁱPr₃)[Si(ⁱPr)₂C(CH₃)=CHCH₃]}{N(SiⁱPr₃)(SiⁱPr₂Et)}][Al{OC(CF₃)₃}₄] (1-Dy), that shows U_eff = 1,843(11) cm^-1 and slow closing of soft magnetic hysteresis loops up to 100 K. Calculations show that the U_eff value for 1-Dy arises from the charge-dense amide ligands, with a pendant alkene taking a structural role to enforce a large N-Dy-N angle while imposing only a weak equatorial interaction. This leads to molecular spin dynamics up to 100 times slower than the current best single-molecule magnets above 90 K.