Magnetic Hysteresis in 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 (1). Treatment of 1 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] (2), with a cationic [(NHAr*)₂Dy]⁺ core. 1 and 2 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 1 and 2 are U_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. Ab initio 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 1 features butterfly hysteresis loops up to 8 K that are closed at zero field at all temperatures probed, 2 exhibits a much higher magnetic blocking temperature of T_B = 19.0 K and substantial coercivity of H_C = 1.03 T. Remarkably, both the T_B and H_C observed for 2 constitute a record for mononuclear single-molecule magnets where the metal is either sandwiched by two arene ligands or stabilized by amide functionalities, respectively.