Trinuclear Ni(II)-Ln(III)-Ni(II) Complexes with Schiff Base Ligands: Synthesis, Structure, and Magnetic Properties

The reaction of the Schiff base ligand o-OH-C(6)H(4)-CH=N-C(CH(2)OH)(3), H(4)L, with Ni(O(2)CMe)(2)·4H(2)O and lanthanide nitrate salts in a 4:2:1 ratio lead to the formation of the trinuclear complexes [Ni(2)Ln(H(3)L)(4)(O(2)CMe)(2)](NO(3)) (Ln = Sm (1), Eu (2), Gd (3), Tb (4)). The complex cations contain the strictly linear Ni(II)-Ln(III)-Ni(II) moiety. The central Ln(III) ion is bridged to each of the terminal Ni(II) ions through two deprotonated phenolato groups from two different ligands. Each terminal Ni(II) ion is bound to two ligands in distorted octahedral N(2)O(4) 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 J(NiGd) = +0.42 cm(−1), D = +2.95 cm(−1) with g(Ni) = g(Gd) = 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 (−ΔS(m)) reaches a maximum of 14.2 J kg(−1) K(−1) at 2 K. A brief literature survey of complexes containing the Ni(II)-Ln(III)-Ni(II) moiety is discussed in terms of their structural properties.