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.
Highlights
The nature and magnitude of the exchange interaction between a 3d metal ion and various 4f metal ions have been the subject of intense investigation in the last decades
Lanthanide ions exhibit large and, in some cases, highly anisotropic magnetic moments, which in combination with different paramagnetic metal ions have led to polynuclear complexes presenting a wide variety of magnetic properties
Thereafter, synthetic strategies were developed for the designed synthesis of dinuclear 3d/4f complexes by Costes [5] and other researchers [6] in order to delve into the nature and magnitude of the magnetic interactions between the metal ions
Summary
The nature and magnitude of the exchange interaction between a 3d metal ion and various 4f metal ions have been the subject of intense investigation in the last decades. The combination of 3d/4f metal ions in one molecule can achieve high spin ground states (via the involvement of the 3d metal ions) along with large single-ion anisotropy (via the presence of the 4f metal ions) and can provide, in most cases, single molecule magnets (SMMs) [1,2], i.e., quantum spin systems with well-defined ground state spin S. Thereafter, synthetic strategies were developed for the designed synthesis of dinuclear 3d/4f complexes by Costes [5] and other researchers [6] in order to delve into the nature and magnitude of the magnetic interactions between the metal ions. It was concluded that in CuLn and NiLn dinuclear complexes the magnetic exchange interaction is antiferromagnetic for the 4f1–5 ions and ferromagnetic for the 4f7–11 ions [6]
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