Mononuclear Lanthanide Complexes: Energy-Barrier Enhancement by Ligand Substitution in Field-Induced Dy^III SIMs

Abstract

The sequential reaction of 2-((6-(hydroxymethyl)pyridin-2-yl)-methyleneamino)phenol (LH), LnCl·6HO, and 1,1,1-trifluoroacetylacetone (Htfa) in the presence of EtN afforded [Ln(LH) (tfa)] [Ln = Dy (1), Ln = Tb (2), and Ln = Gd (3)], while under the same reaction conditions, but in the absence of the coligand, another series of mononuclear complexes, namely, [Ln(LH)]·Cl·2MeOH] [Ln = Dy (4) and Tb (5)] are obtained. Single-crystal X-ray diffraction analysis revealed that the former set contains a mono-deprotonated [LH] and two tfa ligands, while the latter set comprises of two mono-deprotonated [LH] ligands that are nearly perpendicular to each other at an angle of 86.9°. Among these complexes, 2 exhibited a ligand-sensitized lanthanide-characteristic emission. Analyses of the alternating current susceptibility measurements reveal the presence of single-molecule magnet behavior for 1 and 4, in the presence of direct-current field, with effective energy barriers of 4.6 and 44.4 K, respectively. The enhancement of the effective energy barrier of the latter can be attributed to the presence of a large energy gap between the ground and first excited Kramers doublets, triggered by the change in coordination environments around the lanthanide centers.

Lanthanide(III)-Based Single-Ion Magnets

“…Both these complexes show an SMM behavior in the presence of a dc field with anisotropic energy barriers of 4.6 (2000 Oe) and 44.4 K (1000 Oe). 46 The higher U eff value in [Dy(LH) 2 ]·Cl·2MeOH] ( 40 ) is probably due to the strong axial anisotropy, which is indicated by a shorter Dy III –O bond distance in comparison to the other Dy III –donor atom distances.…”

“…Complexes 39 and 40 along with their corresponding energy barrier values. Reprinted with permission from ref (46). Copyright 2017 American Chemical Society.…”

Mononuclear Dysprosium Alkoxide and Aryloxide Single‐Molecule Magnets

“…There has been no Tb alkoxide or aryloxide SMM with CN <6 in the literature to date. Tb SMMs with higher CNs with mainly multi‐dentate chelating aryloxide ligands have been investigated [85, 95, 131–133] . However, they do not show a remarkable improvement over their Dy and Pc counterparts [130, 133] …”

[5×1 + 1×1] Hexanuclear Lanthanide(III) Cocrystal Complexes: Syntheses, Structures, and Magnetic Properties

“…Most recently, Liu and co‐workers has reported molecular magnet behavior of cocrystal containing a tetranuclear metallocage and mononuclear Dy III ‐radical complex . As a matter of fact, there has been a ever‐present interest in the field of lanthanide coordination chemistry due to their promising applications for the development of catalysts and photoluminescent and molecular magnetic materials. Also, multifunctional sensors based on lanthanide complexes have received much attention due to their unique luminescence properties arising from the 4f electrons of Ln(III) ions, large Stokes shift, long lifetimes and sharp emission property .…”