Sandwich-Type Single-Molecule Magnets Complexes of Er(III) with Ansa-Cyclooctatetraenyl Ligands

Abstract

Many sandwich-type lanthanide complexes show extremely high energy barriers ( U _eff) for the reversal of magnetization and high blocking temperatures, being the star molecules in the research area of single-molecule magnets. Herein, the preparation, structural determination, and magnetic property studies of two  ansa-bridged Er-COT (COT = cyclooctatetraenyl dianion) complexes [KDME ₂][Er((η ⁸-COT-Si ^Me2) ₂O)] ( 1) and [KDME ₂][Er((η ⁸-COT-Si i ^Pr2) ₂O)]K[Er((η ⁸-COT-Si i ^Pr2) ₂O)] ( 2) were reported. The Er(III) ions in both complexes are sandwiched by two COT rings which are  ansa-bridged by a [Si-O-Si] group. Magnetic studies reveal both complexes display slow magnetic relaxations with comparable energy barriers (228(5) K for  1, and 196(4) K for  2) and blocking temperatures (10.5 K for both complexes). The difference in the relaxation times ( τ) for the two complexes was studied in details: different molecular vibrations induced by the substituents are the main reason for  τ for  1 being about 10 times longer than for  2 at the same temperature above 10 K, while the quantum tunnelling of magnetization relaxation time ( τ _QTM) for  2 is about 10 times longer than for  1 below 8 K, probably owing to the different dipolar interactions. Further rearrangement of molecular network with such  ansa-bridged SMMs is promising to design molecular magnetic materials with enhanced properties or new properties.

Keywords

Single-molecule magnet / Cyclooctatetraenyl dianion / Sandwich-type complex / Ansa-bridge ligand / Dipolar interaction / Blocking temperature / Quantum tunneling of magnetization / Magnetic relaxation time

RIGHTS & PERMISSIONS

2024 SIOC, CAS, Shanghai, & WILEY-VCH GmbH