Versatile coordination behaviors of a tetrapodal Schiff base ligand scaffold: formation of the dinuclear and trinuclear complexes and their antimicrobial activity

Abstract

Four new complexes have been prepared and characterized from reaction of the tetrapodal Schiff base ligand 1,1,1,1-tetrakis[(3-methoxysalicylaldimino)methyl]methane (H4L) with Cu(II), Ni(II) and Cd(II). X-ray diffraction experiments revealed that 1 ([Cu2L·2H2O]·H2O) and 2 ([Cu2L·2CH3OH]·3H2O) are dinuclear complexes, with the same tetragonal pyramidal coordination geometries around their Cu(II) ions. Complex 3 ([Ni2L]·2H2O) is dinuclear with two square planar Ni(II) ions coordinated to two pairs of the pendant branches of H4L. Complex 4 ([Cd3(HL)2]·3H2O) is a linear trinuclear species with three Cd(II) ions, which were intermolecularly coordinated to three pendant branches of two H4L ligands via an uncommon intermolecular phenoxo oxygen face-sharing mode. The in vitro antimicrobial activities of H4L and its complexes were evaluated against four micro-organisms (Colibacillus, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis) using the tube-dilution method. The results revealed that 3 showed good inhibitory activity against the Gram-positive bacteria S. aureus and B. subtilis with MIC values of 62.5 and 31.0 μg mL, respectively.