Slow Relaxation of Magnetization in an Isostructural Series of Zinc–Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study

Abstract

We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %.

Slow magnetisation relaxation in tetraoxolene-bridged rare earth complexes

“…[60][61][62] Ideally a quantitative study of the mechanisms involved in the magnetic relaxation would require investigation of the samples diluted with a diamagnetic rare earth ion, which is beyond the scope of the present study. 63…”

Multiple Magnetization Reversal Channels Observed in a 3d-4f Single Molecule Magnet

“…Indeed, similar slope (i.e., similar effective barriers) are observed for the measures at the two fields, with only a slight increase in the effective barrier at higher field and a corresponding decrease in the temperature independent contribution [32]. In particular, in the present case, an increase in static field magnitude from 300 Oe to 2 KOe leads to an apparent increase in the effective barrier from 34.4 to 40 K: however, since we included explicitly temperature independent contributions and direct terms in the fits, the two values should ideally be identical [33]. The observed difference should then not be considered as physically significant but possibly portrays the different weights of other unresolved contributions to the relaxation, varying with the field.…”

Heterometallic 3d–4f Complexes as Single‐Molecule Magnets

“…Similarf erromagnetic Ni II -4fi nteractionsa re also anticipated for Ni II -Ln based complexes (4fo rbital containing seven or more electrons). [75] Increase in nuclearity was also achieved by employing a heptadentatel igand N 1 ,N 3 -bis(6-formyl-2-(hydroxymethyl)-4methylphenol)diethylenetriamine (L 23 H 5 ), with two types of distinct coordination pockets, whichl eads to the formation of octanuclear complexes, [Ln III 4 Ni II 4 (H 3 L 23 ) 4 (m 3 -OH) 4 (m-OH) 4 ](Cl) 4 [Ln III = Gd III (116), Tb III (117), Dy III (118)a nd Ho III (119)]. [76] The inner pocket (pocket I) of the ligand accommodates 3d ions whereas the outer pocket (pocketI I) is specific for the 4f ions ( Figure 16).…”