Synthesis, characterization, crystal structures and biological activity of 4-chloro-2-(2-hydroxy-3-ethoxybenzylideneamino)phenol and complexes

Molecular nanoclusters comprising a heterometallic 3d-4f stoichiometry are an interesting class of compounds. In this paper, a chloro-containing Schiff base 4-chloro-2-(2-hydroxy-3-ethoxybenzylideneamino)phenol (H2L) was prepared by condensation reaction of 3-ethoxysalicylaldehyde with 2-amino-4-chlorophenol in methanol. The Schiff base is predisposed to chelate within a cluster core both 3d and 4f metal ions. Reaction of H2L with nickel salts afforded a tetranuclear NiII complex [Ni4L4(MeOH)4] (1), while with nickel salts and lanthanide(III) nitrate three tetranuclear NiII-LnIII complexes [Ni2Eu2L4(NO3)2(DMF)2] (2), [Ni2Er2L4(NO3)2(DMF)2] (3), [Ni2Tb2L4(CH3COO)2(DMF)2]·4DMF (4) were obtained. H2L and the complexes have been characterized by elemental analysis, IR, UV–Vis spectra. H2L has also been characterized by 1H and 13C NMR spectra. Molecular structures of the compounds have been determined by single crystal X-ray determination. In the complexes, the Schiff base ligands coordinate to the metal atoms via ether oxygen, imino nitrogen and two phenolate oxygen atoms. All the Ni atoms in the complexes are in octahedral coordination. The rare earth metal atoms are eight coordinated by the phenolate and ether oxygen of the Schiff base ligands, and anionic and solvent oxygen atoms, forming square antiprismatic coordination. The compounds were evaluated for their antibacterial activities on Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens, and antifungal activities on Candida albicans and Aspergillus niger, and gave interesting results.