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

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.