A new series of unsymmetrical tetradentate Schiff base ligand and its Cu(II), Ni(II) and VO(II) complexes were formed by the condensation of 5-chlorosalicylaldehyde, 2-hydroxy-1-napthaldehyde and 1, 3-diaminopropane-2-ol. The antimicrobial activity of the complexes were tested against four negative bacteria—Klebsiella pneumoniae, Salmonella typhi, Pseudomonas aeruginosa and Escherichia coli, using nutrient agar as medium. The zones of inhibition of the synthesized compounds were compared with the free ligand and the standard streptomycin. All the complexes had higher activity than the free ligand and the standard. The structural assessment of the compounds was carried out based on the elemental analysis and infrared and molar conductivity values.

In order to rectify the microbial resistance to antibiotics, new Schiff base complexes should be prepared. Many of the crude drugs which are sources of medicinal preparations, still originate from wild-growing material. A number of studies have been done on the unsymmetrical tetradentate Schiff base complexes formed by the condensation of diamines with different aldehydes. It is suggested that the compounds may act either by killing or inhibiting the multiplicity of the microbes, or by blocking their active sites (Venkatachalam and Ramesh, 2005; and Nair et al., 2006). The solvent, ligand environment and microorganisms play a major role in the antimicrobial activity. Raman et al. (2007) synthesized a new Mannich base and its metal complexes. They elucidated the structures of both Mannich base and its complexes. Literature survey reveals that no work has been done on the antibacterial effect of this Mannich base and its complexes. Hence, this paper reports the antimicrobial activity of the unsymmetrical tetradentate Schiff base ligand which is enhanced by the presence of metal ion upon coordination.

The ligand was prepared by a standard method. An ethanolic solution (20 mL) of 5-chlorosalicylaldehyde (1.66 g) was mixed with an ethanolic solution (15 mL) of 2-hydroxy-1-naphthaldehyde (1.0 g). The resulting solution was cooled in an ice bath for 30 min. 20 mL ethanolic solution of 1, 3-diaminopropane-2-ol (0.60 g) was added slowly to the above mixture with constant stirring. The mixture was heated under reflux for 1 h and a yellow-colored precipitate separated during refluxion was brought to room temperature. The compound was suction-filtered, washed with ethanol, recrystallized from boiling ethanol and dried (Yusuf et al., 2003) (yield 75%, melting point 243 °C).

The metal ion is bonded by coordinate bonds through the imino nitrogen and oxygen of the phenolic -OH group. The metals selected for the preparation of complexes were copper, nickel and oxovanadium. For each metal complex, different metal salt solutions were prepared. The solutions used for the synthesis of copper, nickel and vanadium complexes were copper per chlorate, nickel per chlorate and vanadyl sulphate, respectively.

Chemistry Journal, Antimicrobial Study, Coordinate Bonds, Structural Assessments, Copper Complexes, Antibacterial Agents, Antimicrobial Activities, Square Planar Geometry, Biological Activities, Biomolecular Spectroscopy, Inorganic Compounds.