A mononuclear and new tetranuclear metal complexes of Zn(II) with Schiff base ligands L1 and L2 respectively, were synthesised. L1 was obtained through the condensation of salicylaldehyde with ortho-phenylenediamine while L2 was the product of reaction between of ortho-vanillin with 2,4,6-trimethyl-m-phenylenediamine. The ligands and complexes were characterised via elemental analysis, melting point, IR and NMR spectroscopy. The shifting of v(C=N), v(C-OH) and v(O-CH3) infrared peaks upon coordination with Zn(II) indicated that these three moieties play a significant role in the complexation. It was found that L1 acted as tetradentate ligand, coordinating with Zn(II) centres through phenolic oxygen and imine nitrogen. The ligand L2 acted as a hexadentate ligand, bonded to metal via phenolic oxygen, imine nitrogen and methoxy oxygen, where four Zn(II) centres formed bridges to connect two ligands.
A symmetrical azomethine ligand L was synthesised from a reaction of m-phenylenediamine and o-vanillin in 1:2 molar ratio. Dinuclear complexes of Zn2L2 and Co2L2 have been successfully isolated and characterised through 1H NMR, IR and magnetic moment. The x-ray crystal structure of Zn2L2 showed that the two Zn(II) nuclei were coordinated to two L moieties through the phenolic oxygen and imine nitrogen atoms, forming a slightly distorted tetrahedral geometry around the Zn(II) centres. When coordinated to metal centres, the signature n(C=N) of Lat 1616 cm-1 experienced a shift towards lower wave numbers of 1573-1613 cm-1. The Zn(II) complex was diamagnetic whereas the Co2L2 complex was paramagnetic with 3 unpaired electrons having µeff = 4.07 B.M. An antibacterial screening against methicillin resistant Staphylococcus aureus (MRSA) revealed that the activity of the complexes was more pronounced than that of the uncoordinated L. The complex Zn2L2 revealed the lowest MIC value of 0.56 µg/µl MIC, indicating that it was a better bactericides than Co2L2 and L, in that order.