A new series of transition metal complexes of Mn (II), Co (II), Ni (II) and Cu (II) are synthesized from a new novel macro cyclic Schiff base ligand with four N donor atoms derived from 4-aminoantipyrine, vanillin and o-phenylenediamine. Several tools like elemental analysis, molar conductance methods, Infrared, electronic (UV-Vis), Electron spin resonance (ESR) and Nuclear Magnetic Resonance (NMR) spectroscopic techniques, thermo gravimetric analysis were used to investigate the chemical structure of the prepared ligand (L) and complexes. The elemental analysis data suggest the formation of 1:1 (M: L) anionic complex with formula [ML]Cl2 (M=Co(II) and [ML]SO4 (M= Mn (II), Ni (II) and Cu (II)). The higher molar conductivity values support the electrolytic nature of the complexes. The infrared spectral studies reveal that the involvement of azomethine nitrogen (-C=N) is coordinated to the metal resulted in to MN4 chromospheres. The electronic absorption spectra of the complexes suggest a square planar geometry around the central metal ion. The NMR parameters of the free ligand and its Zinc (II) complexes were also compared. The X-band ESR spectra of Copper (II) complexes were recorded and the molecular orbital coefficients like g||, g┴ ,Exchange interaction term (G), the covalence parameter (α2), K, K┴ and K2 etc., were calculated. The thermal decomposition parameters of these complexes are also studied in static air atmosphere with a heating rate of 20°C per minute which represents a single stage decomposition with metal oxides as stable residue. Antibacterial screening tests were also performed against bacteria. The comparative study of MIC values of the Schiff’s base and its metal complexes indicate that the metal complexes exhibit greater antibacterial activity than the free ligand.
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