Microwave synthesis and spectral, thermal and antimicrobial activities of some novel transition metal complexes with tridentate Schiff base ligands

Some novel Schiff base metal complexes of Cr(III), Co(II), Ni(II) and Cu(II) derived from 2-[(5-bromo-2-hydroxybenzylidene)amino]pyridin-3-ol (BSAP) and {5-chloro-2-[((2-hydroxy-1-naphthyl)methylene)amino]phenyl}-phenylmethanone (HNAC) were synthesized by conventional as well as microwave methods. These compounds were characterized by elemental analysis, FT-IR, FAB-mass, electronic and ESR spectroscopy, molar conductance, magnetic susceptibility, thermal, cyclic voltammetric and electrical conductivity measurements and XRD analyses. Analytical data revealed that all the complexes exhibited 1:1 (metal:ligand) ratio with a coordination number of 4 or 6. The IR data showed that the ligand coordinates with the metal ions in a tridentate manner. FAB-mass and thermal data showed the degradation pattern of the complexes. The thermal behaviour of the metal complexes showed that the hydrated complexes lose water molecules of hydration in the first step; with decomposition of the ligand molecules in the subsequent steps. The crystal system, lattice parameters, unit cell volume and number of molecules in a unit cell in the lattice of the complexes were determined by XRD analysis. XRD patterns indicated a crystalline nature for the complexes. The solid state electrical conductivity of the metal complexes was also measured. Solid state electrical conductivity studies reflected a semi-conducting nature of the complexes. The Schiff base and metal complexes displayed good activity against the Gram-positive bacteria Staphylococcus aureus, the Gram-negative bacteria Escherichia coli and the fungi Aspergillus niger and Candida albicans. The antimicrobial results also indicated that the metal complexes displayed better antimicrobial activity as compared to the Schiff bases.