Low-coordinate bis(imidazolin-2-iminato) dysprosium(iii) single-molecule magnets

Abstract

Lanthanide-based single-molecule magnets (Ln-SMMs) have become the most conspicuous SMMs exhibiting the highest effective barrier (U_eff) and blocking temperature (T_B). Different strategies have been proposed to construct high-performance SMMs, including reducing the coordination number to generate high-order local symmetry and weakened molecular vibrations, thus reducing the possibility of spin–vibration interaction. However, the synthesis of low-coordinate Ln(III) complexes is still very challenging owing to their large ionic radius and ionic nature, especially when the coordination number is lower than five. Herein, two bis(imidazolin-2-iminato) dysprosium(III) SMMs [Dy(Im^DippN)₂(Bn)(THF)] (1) and [Dy(Im^DippN)₂(BPh₄)] (2) (Im^DippNH = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine, Bn = benzyl) were synthesized and characterized. The four-coordinate complex 1 possessed a U_eff of 593 K and a T_B of 8 K, while complex 2 exhibited a U_eff of 343 K. The weaker equatorial crystal field in 1 than 2 could suppress the quantum tunneling of magnetization (QTM), leading to a higher U_eff. Moreover, calculations on model structures indicated that constructing bis(imidazolin-2-iminato) single-molecule magnets with a higher U_eff and T_B is possible by further regulating the electronic effects and steric hindrance of imidazolin-2-iminato ligands.