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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 DyIII 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 DyIII 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 Ueff = 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 DyIII 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 TB = 19.0 K and substantial coercivity of HC = 1.03 T. Remarkably, both the TB and HC 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.
