Auxiliary Ligands Modulated Bis(imidazolin-2-iminato) Dysprosium Single-Molecule Magnets

A systematic study on the magneto-structural correlation plays an essential role in improving the molecular design of single-molecule magnets (SMMs). Strong axial crystal fields on Dy(III) could help enhance the uniaxial magnetic anisotropy, increasing the relaxation barrier and magnetic blocking temperature, while transverse crystal-field interactions accelerate magnetic relaxation. The imidazolin-2-iminato ligands have been viewed as promising strong-field ligands to construct high-performance Dy(III) SMMs since the large steric hindrance and strong donating capacity make imidazolin-2-iminato ligands possibly impede weak transverse interactions at equatorial positions. Herein, we synthesize a series of bis(imidazolin-2-iminato) Dy(III) SMMs with magneto-structural correlations revealed by combined magnetic and theoretical analyses. The relaxation barriers of these complexes vary over a wide range, indicating that auxiliary ligands at equatorial positions could effectively modulate SMM performance. Additionally, we found that two parameters, the relaxation energy barrier and the Dy–N bond length, follow specific correlation patterns with the N–Dy–N angle, and these correlations exhibit precisely opposite trends. The highest U_eff can be reached when the N–Dy–N angle is approximately 121°, suggesting the greatest potential of this series of complexes.