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.