Magnetic Hysteresisin a Dysprosium Bis(amide) Complex

Here, we present the synthesis and characterization of two mononuclear dysprosium molecules. The first complex is neutral and contains two triarylamide ligands coordinating to a Dy^III ion that is additionally ligated to a chloride anion, in the form of (NHAr*)₂DyCl (<b>1</b>). Treatment of <b>1</b> with Tl[BArF₂₄] prompted the removal of the chloride as TlCl from the first coordination sphere to afford the mononuclear Dy^III complex, [(NHAr*)₂Dy][BArF₂₄] (<b>2</b>), with a cationic [(NHAr*)₂Dy]⁺ core. <b>1</b> and <b>2</b> were investigated through single-crystal X-ray diffraction analysis, UV–vis spectroscopy, and SQUID magnetometry. Both compounds are single-molecule magnets with magnetic hysteresis. The determined effective spin-reversal barriers and preattempt times for <b>1</b> and <b>2</b> are <i>U</i>_eff = 601(2) cm^–1 and 598(2) cm^–1, and τ₀ = 4.2(1) × 10^–10 s and 3.1(2) × 10^–10 s, respectively. <i>Ab initio</i> calculations were conducted on both molecules which uncovered the energy of the crystal field states of Dy^III and affirmed the effective energy barrier height. Notably, the extrusion of the halide ion has huge ramifications on the magnetic relaxation: While <b>1</b> features butterfly hysteresis loops up to 8 K that are closed at zero field at all temperatures probed, <b>2</b> exhibits a much higher magnetic blocking temperature of <i>T</i>_B = 19.0 K and substantial coercivity of <i>H</i>_C = 1.03 T. Remarkably, both the <i>T</i>_B and <i>H</i>_C observed for <b>2</b> constitute a record for mononuclear single-molecule magnets where the metal is either sandwiched by two arene ligands or stabilized by amide functionalities, respectively.