Significant Enhancement of Energy Barriers in Dinuclear Dysprosium Single-Molecule Magnets Through Electron-Withdrawing Effects

TLDR

The study investigates how electron‑withdrawing ligands affect the energy barriers of single‑molecule magnets. Five new dinuclear Dy₂ phenoxo‑bridged SMMs with varied terminal ligands were synthesized and their structural and magnetic properties compared to a previously studied Dy₂ SMM. Introducing electron‑withdrawing ligands markedly increased the energy barriers, with the CF₃COCHCOCF₃ ligand (complex 6) producing a seven‑fold rise, attributed to more axial g tensors and higher‑energy first excited Kramers doublets.

Abstract

The effect of electron-withdrawing ligands on the energy barriers of Single-Molecule Magnets (SMMs) is investigated. By introducing highly electron-withdrawing atoms on targeted ligands, the energy barrier was significantly enhanced. The structural and magnetic properties of five novel SMMs based on a dinuclear {Dy2} phenoxo-bridged motif are explored and compared with a previously studied {Dy2} SMM (1). All complexes share the formula [Dy2(valdien)2(L)2]·solvent, where H2valdien = N1,N3-bis(3-methoxysalicylidene) diethylenetriamine, the terminal ligand L = NO3– (1), CH3COO– (2), ClCH2COO– (3), Cl2CHCOO– (4), CH3COCHCOCH3– (5), CF3COCHCOCF3– (6), and solvent = 0.5 MeOH (4), 2 CH2Cl2 (5). Systematic increase of the barrier was observed for all complexes with the most drastic increase seen in 6 when the acac ligand of 5 was fluorinated resulting in a 7-fold enhancement of the anisotropic barrier. Ab initio calculations reveal more axial g tensors as well as higher energy first excited Kramers doublets in 4 and 6 leading to higher energy barriers for those complexes.