Opening Magnetic Hysteresis by Axial Ferromagnetic Coupling: From Mono-Decker to Double-Decker Metallacrown

Combining Ising-type magnetic anisotropy with collinear magnetic interactions in single-molecule magnets (SMMs) is a significant synthetic challenge. Herein we report a Dy[15-MCCu-5] (1-Dy) SMM, where a Dy-III ion is held in a central pseudo-D-5h pocket of a rigid and planar Cu-5 metallacrown (MC). Linking two Dy[15-MCCu-5] units with a single hydroxide bridge yields the double-decker {Dy[15-MCCu-5]}(2) (2-Dy) SMM where the anisotropy axes of the two Dy-III ions are nearly collinear, resulting in magnetic relaxation times for 2-Dy that are approximately 200 000 times slower at 2 K than for 1-Dy in zero external field. Whereas 1-Dy and the Y-III-diluted Dy@2-Y analogue do not show remanence in magnetic hysteresis experiments, the hysteresis data for 2-Dy remain open up to 6 K without a sudden drop at zero field. In conjunction with theoretical calculations, these results demonstrate that the axial ferromagnetic Dy-Dy coupling suppresses fast quantum tunneling of magnetization (QTM). The relaxation profiles of both complexes curiously exhibit three distinct exponential regimes, and hold the largest effective energy barriers for any reported d-f SMMs up to 625 cm(-1).

Automated summary

In this study, a Dy[15-MCCu-5] (1-Dy) single-molecule magnet (SMM) and a double-decker {Dy[15-MCCu-5]}(2) (2-Dy) SMM were reported. The anisotropy axes of the two Dy-III ions in 2-Dy are nearly collinear, resulting in significantly slower magnetic relaxation times compared to 1-Dy. These complexes exhibit three distinct exponential regimes in their relaxation profiles and hold the largest effective energy barriers among reported d-f SMMs, up to 625 cm(-1).