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

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.

Tuning of Hula-Hoop Coordination Geometry in a Dy Dimer

“…The energy barriers of compound 1 and 2 are lower, which may be due to the coordinating anions which are different from those in 3 to 6. A similar behaviour has been previously observed in a Dy dimer system [25]. Also, the axial solvent molecule contributes to this effect in terms of different energy barrier heights [29].…”

“…However, for 2, a good fit was obtained according to the Debye model. The α values are below 0.33 (Table S2) which indicates a relatively narrow width of relaxation processes most likely due to a combination of QTM and thermally assisted relaxation pathways [25].…”

“…However, for 2, a good fit was obtained according to the Debye model. The α values are below 0.33 (Table S2) [25].…”

Modulating the Slow Relaxation Dynamics of Binuclear Dysprosium(III) Complexes through Coordination Geometry

“…Most of the reports on Ln-based SMMs concentrated mainly on either changing the Ln ion keeping the ligand system constant [18][19][20] or changing the ligand but keeping the coordination environment around the Ln ion unchanged [8]. Only few studies are known where modification in the ligand system was done to tune the relaxation behavior in the complexes [21][22][23][24][25][26]. In this paper, differences in slow relaxation of the magnetization behavior were explored in two Dy III dinuclear complexes, where minor changes in the coordination environment around the Dy III ions disturbed the local symmetry.…”

Polyoxometalate-Supported Lanthanoid Single-Molecule Magnets

“…[52,53] The simultaneous coordination of both POM and organic ligands to lanthanoid centres may also be pursued to access new coordination environments and crystal fields. Varying the redox state of the coordinating ligands has proved important for Ln-SMMs with organic ligands, [54,55] but is yet to be explored for Ln-POM SMMs, with the rich redox chemistry of POMs very promising in this regard.…”