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.