Trinuclear NiII-LnIII-NiII Complexes with Schiff Base Ligands: Synthesis, Structure, and Magnetic Properties

Abstract

The reaction of the Schiff base ligand o-OH-C6H4-CH=N-C(CH2OH)3, H4L, with Ni(O2CMe)2∙4H2O and lanthanide nitrate salts in a 4 : 2 : 1 ratio lead to the formation of the trinuclear complexes [Ni2Ln(H3L)4(O2CMe)2](NO3) (Ln = Sm (1), Eu (2), Gd (3), Tb (4)). The complex cations contain the strictly linear NiII-LnIII-NiII moiety. The central LnIII ion is bridged to each of the terminal NiII ions through two deprotonated phenolato groups from two different ligands. Each terminal NiII ion is bound to two ligands in distorted octahedral N2O4 environment. The central lanthanide ion is coordinated to four phenolato oxygen atoms from the four ligands, and four carboxylato oxygen atoms from two acetates which are bound in the bidentate chelate mode. The lattice structure of complex 4 consists of two interpenetrating, supramolecular diamond like lattices formed through hydrogen bonds among neighboring trinuclear clusters. The magnetic properties of 1-4 were studied. For 3 the best fit of the magnetic susceptibility and isothermal M(H) data gave JNiGd = +0.42 cm−1, D = +2.95 cm−1 with gNi = gGd = 1.98. The ferromagnetic nature of the intramolecular Ni···Gd interaction revealed ground state of total spin S = 11/2. The magnetocaloric effect (MCE) parameters for 3 show that the change of the magnetic entropy (−ΔSm) reaches a maximum of 14.2 J kg−1 K−1 at 2 K. A brief literature survey of complexes containing the NiII-LnIII-NiII moiety is discussed in terms of their structural properties.

Synthesis, Crystal Structures and Magnetic Properties of Trinuclear {Ni2Ln} (LnIII = Dy, Ho) and {Ni2Y} Complexes with Schiff Base Ligands

“…Previously we have reported the trinuclear complexes [Ni 2 Ln(H 3 L) 4 (O 2 CMe) 2 ](NO 3 ) (Ln III = Sm, Eu, Gd, Tb), which were isolated by the 4: [19]. The crystal structure of the {Ni 2 Tb} complex revealed that the Tb III ion is linked to each of the Ni II ions via two O phenolato atoms of the (H 3 L) − ligands and contains a strictly linear Ni II -Tb III -Ni II moiety.…”

“…The last examples indicate that the introduction of chirality in a magnetic system is a probable route to multifunctionality as in the case of transition metal complexes [2]. As the trinuclear mixed 3d/4f metal systems have provided interesting examples with SMM properties [16,17], recently we have focused our research on the Ni II -Ln III -Ni II system [18,19]. In these series of compounds, there are examples which present also SMM properties [20][21][22][23] or the magnetocaloric effect [24].…”

“…In these series of compounds, there are examples which present also SMM properties [20][21][22][23] or the magnetocaloric effect [24]. The crystal structure study of the series of [Ni 2 Ln(H 3 L) 4 (O 2 CMe) 2 ](NO 3 ) (Ln = Sm, Eu, Gd, Tb)] complexes [19] indicate that all the compounds are isomorphous and they crystallize in the centrosymmetric orthorhombic space group Pnnn and the study of their magnetic properties study indicate that the Ln III = Gd complex presents magnetocaloric behavior. Based on the literature survey for the linear Ni II -Ln III -Ni II system presented in [18], there are cases where the complexes are chiral and, as they crystallize in centrosymmetric space groups, both enantiomers exist in the structure [25,26].…”

“…In this study we present the synthesis, crystallographic characterization and magnetic properties of three complexes [Ni 2 Ln(H 3 L) 4 (O 2 CMe) 2 ](NO 3 ) (Ln = Dy (1), Ho (2), and Y (3)) which were synthesized following the same synthetic paths as previously described [19], but all three complexes crystallize in the non-centrosymmetric Pna2 1 space group which belongs to the mm 2 point group (following the standard notation). This point group, along with the axial and the m point groups, belong to the seven point groups which lie in the section where interesting electrical or optical properties could coexist.…”

In Situ Assembled Polynuclear Zinc Oxo Clusters Using Modified Schiff Bases as Ligands

“… 7 Using Schiff base/modified vanillin-based Schiff bases, several multinuclear complexes of d/f block elements have been reported. 8 Notable reports among them are multinuclear dysprosium-based clusters reported by Murugesu et al, who synthesized a series of tetranuclear butterfly core-containing dysprosium clusters, and the magnetic measurements revealed that some of these clusters displayed a high energy barrier for reversal of magnetization. 9 In this backdrop, Schiff-base ligands have been used for synthesizing zinc-based multinuclear clusters, some of which have shown interesting applications as polymerization catalysts, 10 reagents in organic synthesis, 11 molecular precursors for ZnO-based materials, 12 models of the active site in zinc enzymes, 13 and in synthesizing functional molecule-based materials.…”