Aggregation of heptanuclear [MII7] (M = Co, Ni, Zn) clusters by a Schiff-base ligand derived from o-vanillin: Synthesis, crystal structures and magnetic properties

Abstract

Three transition metal heptanuclear clusters, [Co7L6(μ3-OCH3)6](ClO4)2·H2O (1), [Ni7L6(μ3-OH)6](ClO4)2·4DMF (2), [Zn7L6(μ3-OCH3)6](ClO4)2 (3), have been obtained using a new Schiff base ligand (HL) derived from o-vanillin and 2-methoxybenzylamine. The structures of 1–3 have been determined based on single crystal X-ray diffraction studies. They have similar wheel structures in which six metal ions locate on the rim with the seventh metal ion in the center. Complex 3 exhibits luminescence in the solid state at room temperature. Variable-temperature DC and AC magnetic studies were carried out on polycrystalline samples of 1 and 2. Compound 1 shows an overall ferromagnetic coupling and absence of SMM behavior despite the observation of out-of-phase susceptibility in external applied field. The analysis of the magnetic data for compound 2 emphasizes the interplay of ferromagnetic interactions between central and peripheral nickel(II) ions (J1 = −11.2 cm−1), and antiferromagnetic interactions between the peripheral nickel(II) ions (J2 = 9.6 cm−1); H = ΣJijSiSj.