Large Spin-Relaxation Barriers for the Low-Symmetry Organolanthanide Complexes [Cp2Ln(BPh4)] (Cp=pentamethylcyclopentadienyl; Ln=Tb, Dy)

Single‐molecule magnets comprising one spin center represent a fundamental size limit for spin‐based information storage. Such an application hinges upon the realization of molecules possessing substantial barriers to spin inversion. Axially symmetric complexes of lanthanides hold the most promise for this due to their inherently high magnetic anisotropies and low tunneling probabilities. Herein, we demonstrate that strikingly large spin reversal barriers of 216 and 331 cm−1 can also be realized in low‐symmetry lanthanide tetraphenylborate complexes of the type [Cp*2Ln(BPh4)] (Cp*=pentamethylcyclopentadienyl; Ln=Tb (1) and Dy (2)). The dysprosium congener showed hysteretic magnetization data up to 5.3 K. Further studies of the magnetic relaxation processes of 1 and 2 under applied dc fields and upon dilution within a matrix of [Cp*2Y(BPh4)] revealed considerable suppression of the tunneling pathway, emphasizing the strong influence of dipolar interactions on the low‐temperature magnetization dynamics in these systems. Two organometallic complexes with very low molecular symmetry possess some of the largest‐magnitude spin reversal barriers known for complexes of DyIII and TbIII ions. This observation is unexpected due to the general correlation between large barriers and high molecular symmetries. On account of the large barriers, sluggish spin reversal was observed, leading to blocking and magnetic hysteresis at low temperature (see figure).