Face-Sharing Heterotrinuclear M^II−Ln^III−M^II (M = Mn, Fe, Co, Zn; Ln = La, Gd, Tb, Dy) Complexes: Synthesis, Structures, and Magnetic Properties

Abstract

Trinuclear linear 3d-4f-3d complexes (3d = Mn(II), Fe(II), Co(II), Zn(II) and 4f = La(III), Gd(III), Tb(III), Dy(III)) were prepared by using a tripodal nonadentate Schiff base ligand, N,N',N''-tris(2-hydroxy-3-methoxybenzilidene)-2-(aminomethyl)-2-methyl-1,3-propanediamine. The structural determinations showed that in these complexes two distorted trigonal prismatic transition metal complexes of identical chirality are assembled through 4f cations. The Mn and Fe entities crystallize in the chiral space group P2(1)2(1)2(1) as pure enantiomers; the cobalt complexes exhibit a less straightforward behavior. All Mn, Fe, and Co complexes experience M(II)-Ln(III) ferromagnetic interactions. The Mn-Gd interaction is weak (0.08 cm(-1)) in comparison to the Fe-Gd (0.69 cm(-1)) and Co-Gd (0.52 cm(-1)) ones while the single ion zero field splitting (ZFS) term D is larger for the Fe complexes (5.7 cm(-1)) than for the cobalt ones. The cobalt complexes behave as single-molecules magnets (SMMs) with large magnetization hysteresis loops, as a consequence of the particularly slow magnetic relaxation characterizing these trinuclear molecules. Such large hysteresis loops, which are observed for the first time in Co-Ln complexes, confirm that quantum tunnelling of the magnetization does not operate in the Co-Gd-Co complex.

Theoretical Understanding of Anisotropy in Molecular Nanomagnets

“…20) shows that its top corresponds to ca 12 cm À1 [102], which is in good agreement with the value extracted from experiment [110]. The high SMM performance of this complex [110] is explained by a multilevel structure of the exchange barrier, as was also the case of the Cr 2 Dy 2 complex considered above. + .…”

“…As an example of a "non-lanthanide" mixed complex, Fig. 19a shows a trinuclear complex from the series [LCo II LnCo II L] + [110], where L ¼ N,N 0 ,N 00 -tris(2-hydroxy-3-methoxybenzylidene)-2-(aminomethyl)-2-methyl-1,3-propanediamine, for Ln ¼ Gd. In this series, owing to the structure of L, the complexes possess an almost ideal trigonal axis connecting the three metal ions.…”

Effect of Magnetic Coupling on Water Proton Relaxivity in a Series of Transition Metal GdIII Complexes

“…38–41 In principle, for a complex that features magnetic exchange between Gd III and a paramagnetic transition metal ion, the decrease in T 1e of the Gd III ion induced by exchange coupling varies with the spin quantum number of the transition metal ( S TM ), the exchange constant ( J ) of the coupling, and the electronic relaxation time of the transition metal ( T 1e ′). 28,30,42 Accordingly, the coupling constant ( J ) and the electronic structure of the transition metal ( S TM and T 1e ′) can be synthetically tuned to modulate T 1e of Gd III .…”

“…Therefore, we selected a series of salen-based dinuclear complexes of the general formula LMGd( μ -O 2 CCH 3 )(O 2 CCH 3 ) 2 41,43 (Figure 1) to investigate the correlation between M and the resulting T 1e of Gd III . Here, we should note that these complexes are intended to demonstrate a proof-of-concept and are not suitable for direct use in a biological system.…”

Edta-linked 5p–4f trinuclear heterometallic complex: syntheses, X-ray structure and luminescent properties

“…Research on the design and synthesis of multifunctional metal-organic frameworks (MOFs) has received attention for fascinating structures and potential applications, such as functional materials in magnetism, non-linear optics, sensors, catalysis, and chemical separations [1][2][3][4][5]. Multidentate ligands such as ethylenediaminetetraacetate (edta) are good choice for constructing heterometallic frameworks due to the existence of different bridging modes.…”