Magnetic Hysteresis at 31 K in a Four-Coordinate Dysprosium(III) Amide Complex

The state-of-the-art in single-molecule magnet (SMM) design is dominated by charged dysprosium sandwich complexes with mono- or dianionic π-ligands and which exhibit some of the highest open-loop magnetic hysteresis temperatures (TH), the highest 100 s blocking temperatures (TB100) and some of the largest barriers to magnetic reversal (Ueff). Architectures that leverage more charge-dense ligands, such as amides or alkoxides, with axial coordination and weak equatorial interactions can generate larger crystal fields (CFs), and hence larger Ueff values; however, this is often not accompanied by correspondingly high TH or TB100 values. Here we report a four-coordinate dysprosium (III) single-molecule magnet, DyMe2Si (NSiiPr3) 22K (toluene) 2n (1Dy), with charge-dense amide donors, but a coordination environment that is between axial and tetrahedral in structure. Nevertheless, 1Dy displays open-loop magnetic hysteresis up to 31 K using sweep rates of 22 Oe s–1. The coercive field (HC) is 1. 65 T at 1. 8 K, and TB100 = 10 K. Ab initio calculations show the four-coordinate geometry imparts a strong axial CF as the 6H15/2 spin-orbit multiplet is split over 1, 958 K (1, 361 cm–1). The experimental Ueff (742 K, 516 cm–1) is smaller and resides between the second and third excited Kramers doublets, indicating the presence of through-barrier relaxation pathways. Non-Kramers ion analogues 1Tb and 1Ho show waist-restricted hysteresis and short relaxation times at all temperatures. The magnetic properties of 1Dy place it highly amongst monometallic lanthanide SMMs using an alternative design strategy, which is synthetically simple and may be further refined.