Probing the Origin of Ferro-/Antiferromagnetic Exchange Interactions in Cu(II)–4f Complexes

Abstract

The mechanistic investigations between Cu(II) and the anisotropic lanthanides (Ln(III)) are not much explored to date. This is due to the complicated energy spectrum which arises due to the orbital angular momentum of anisotropic lanthanides. Interestingly, the exchange coupling J in Ln(III)−Cu(II) systems was found to be antiferromagnetic for <4f 7 metal ions and ferromagnetic for ≥4f 7 metal ions, while the net magnitude of J Total strength gradually decreases moving from f 1 to f 13 . While this is established in several examples, the reason for this intriguing trend is not rationalized. In this article, we have taken up these challenging tasks by synthesizing a family of complexes with the general molecular formula [Cu 2 Ln(HL) 4 (NO 3 )](NO 3 ) 2 , where Ln = La (1 -La ), Ce (2 -Ce ), Pr (3 -Pr ), Gd (4 -Gd ), Tb (5 -Tb ), Dy (6 -Dy ), and Ho (7 -Ho ) and HL = C 15 H 15 N 1 O 3 ; (2methoxy-6-[(E)-2′-hydroxymethyl-phenyliminomethyl]-phenolate) is a monodeprotonated tridentate Schiff base ligand. Detailed dc magnetic susceptibility measurements performed for all the complexes reveal that the Cu(II) ion is coupled ferromagnetically to the respective Ln(III) ion, which has more than seven electrons in the 4f shell, while an antiferromagnetic coupling is witnessed if Ln(III) has less than seven electrons. The strength of the exchange coupling constant was quantitatively determined for representative complexes from the high-field/high-frequency electron paramagnetic resonance spectroscopy which follows the order of 4 -Gd (1.50(10) cm −1 ) > 5 -Tb (1.18(10) cm −1 ) > 6 -Dy (0.56(10) cm −1 based on the −

New Heterotrinuclear CuIILnIIICuII (Ln = Ho, Er) Compounds with the Schiff Base: Syntheses, Structural Characterization, Thermal and Magnetic Properties

“…As shown in Figure 9, this value decreases by lowering the temperature to 8.05 cm 3 Kmol −1 at 1.8 K. The reduction of χ M T at low temperature should mainly arise from the crystal field splitting of Ln III ions and/or combine the contribution of the overall antiferromagnetic interactions among the metal ions. These results are compatible with the empirical investigations of heterometallic Cu II -4f compounds, in which the 4f ions show a spin-orbit coupling [32,[61][62][63].…”

“…The values of magnetization rise quickly at the low magnetic field whereas at the high magnetic field, the increase of magnetization is slow and linear. The magnetization reaches the values 6.5 µ B for 1 and 7.0 µ B for 2, respectively, at 5T; these are far from the theoretical saturated values anticipated for one uncoupled lanthanide(III) ion and two copper(II) ions [32,[61][62][63].…”

Interplay between anisotropy and magnetic exchange to modulate the magnetic relaxation behaviours of phenoxo bridged Dy2dimers with axial β-diketonate co-ligands

“…In accordance with the current literature review, it emerges that multidentate Schiff base ligands with distinct coordination environments have been effectively applied in the assembly of polynuclear heterometallic 3d/4f 61–75 and homometallic 4f complexes. 57,76–85 Utilizing the above-mentioned knowledge, we have applied ( E )-2-((pyridin-2-ylmethylene)amino)phenol (LH) in order to construct homometallic lanthanide complexes.…”

Electronic Structure and Magneto-Structural Correlations Study of Cu2UL Trinuclear Schiff Base Complexes: A 3d–5f–3d Case

“…Since the discovery of ferromagnetic interactions in trinuclear Cu 2 Gd complexes in 1985, , the heterometallic 3d–4f complexes have attracted intense attention, both from experimental and theoretical sides, due to their many unique and specific potential applications in catalysis, magnetic cooling materials, and luminescence, and notably as high spin molecules, which could behave as single-molecule magnets (SMM). − In particular, the combination of 3d and 4f elements to form large cluster aggregates has produced several novel SMMs with attractive blocking temperatures and thus a slow relaxation of magnetization. − Besides its fundamental aspects, the exchange coupling between a 4f ion and a spin carrier, a 3d ion or an organic radical has been studied with the aim of working out an accurate theoretical description of an effective magnetic interaction. − However, it seems difficult to envision high-nuclearity lanthanide clusters with concerted spin behavior. − The poor overlap of the contracted lanthanide 4f orbitals with bridging ligand orbitals, mostly results in weak magnetic exchange coupling. ,, …”