Two Types of Hexanuclear Partial Tetracubane [Ni₄Ln₂] (Ln = Dy, Tb, Ho) Complexes of Thioether-Based Schiff Base Ligands: Synthesis, Structure, and Comparison of Magnetic Properties

Abstract

New Schiff base ligand H2L containing N2O4S donor atoms has been explored for its ability to provide complexes of selected 3d and 4f metal ions. Room temperature reaction of H2L with NiCl2·6H2O and Ln­(NO3)3·5H2O in the presence of Et3N in MeCN–MeOH (2:1) medium resulted in [Ni4Ln2(L)2(μ-Cl)2(μ3-OH)4(H2O)6]­Cl4·2H2O (where Ln = Dy3+ (1), Tb3+ (2), and Ho3+ (3) and H2L = 2-((2-(2-(2-hydroxy-3-methoxybenzylideneamino)­ethylthio)­ethylimino)­methyl)-6-methoxyphenol). Use of Ni­(SCN)2·4H2O during synthesis provided SCN– ions for bridging and terminal coordination in [Ni4Ln2(L)2(μ-NCS)2(μ3-OH)4(NCS)4(H2O)2]·xMeOH·yH2O (where Ln = Dy3+ (4), x = 2, y = 4; Tb3+ (5) and Ho3+ (6), x = 0, y = 14.1). All six complexes possess a hexanuclear defective tetracubane topology having exchangeable bridging groups. The study of direct current magnetic susceptibility measurements revealed that the Ni­(II) ions are engaged in ferromagnetic interaction with the DyIII, TbIII, and HoIII ions and have significant magnetic anisotropy in all six complexes. Alternating current susceptibility measurements confirmed that both of the two types of compounds qualify as zero-field single-molecule magnets (SMMs), and the effective barrier for the reversal of the magnetic moment was found to be in the range U eff = 23–31 K for 1–2 and 4–5, respectively. Detailed insight into the electronic structure and magnetic properties was calculated using DFT- and CASSCF-based analyses. The found isotropic exchange parameter (J) values are J Ni–Ni = −4.7 cm–1 for 1 and J Ni–Ni = +29.2 cm–1 for 4 and clearly indicate that the μ-NCS-bridge is a better candidate than μ-Cl for ferromagnetic exchange interactions. Out of the six complexes, only complex 5 displays TbIII centered emission peaks at 451 and 480 nm.

Pentanuclear Spirocyclic Ni4Ln Derivatives: Field Induced Slow Magnetic Relaxation in the Dysprosium and Erbium Analogues

“…Due to the phenomenon of lanthanide contraction the bond lengths in and around the lanthanide centres display the predictable general tendency that is towards shorter values over the series 2 – 5 (Table S7). From the knowledge base of Ni–Ln compounds, synthetic methods offer a variety of topology with different levels of control in the design. To the best of our knowledge, only six pentanuclear Ni–Ln heteronuclear complexes, (Figure ) are found whose detailed magnetic analysis has been done.…”

Carboxylate-Decorated Aggregation of Octanuclear Co4Ln4 (Ln = Dy, Ho, Yb) Complexes from Ligand-Controlled Hydrolysis: Synthesis, Structures, and Magnetic Properties

“…An axially symmetric crystal field around the 4f ions and strong exchange coupling between paramagnetic centers usually promote the SMM behavior. , Co II ( S = 3/2) is a Kramers ion, and the anisotropy in most octahedral Co II complexes is generated from large and positive D values . At the same time, many of the 4f ions too exhibit strong magnetic anisotropy, such as Tb III ( 7 F 6 ), Dy III ( 6 H 15/2 ), and Ho III ( 5 H 8 ) and can be chosen for the synthesis of Co II -4f category CAs.…”

Hexanuclear Co4Dy2, Zn4Dy2, and Co4Y2 Complexes with Defect Tetracubane Cores: Syntheses, Structures, and Magnetic Properties

“…Meanwhile, the 3d metals, such as Co II and Ni II also contribute anisotropy to the 3d–4f clusters [38–40] . It is found that the magnetic interactions of many 3d–4f complexes are often ferromagnetic [41–44] . All these properties are favorable for 3d–4f compounds to behave as SMMs.…”