A new borate ligand potassium bis (succinyl) borate (KL) has been synthesized by reaction of potassium borohydride and succinic acid in methanol solution. It was converted into its Co(II), Ni(II) and Cu(II) dinuclear complexes by mixing and stirring with MeOH solution of metal chloride salts. The compounds have been characterized by elemental analysis, spectral studies (IR, NMR, UV-vis, ESI mass spectra and EPR), magnetic susceptibility and thermogravimetric analysis (TGA). Spectroscopic results supported a square planar geometry in the Cu(II) complex while octahedral geometry in case of the Co(II) and Ni(II) complexes. In the light of these results, it is suggested that ligand acts as monoanionic tetradentate and coordinate to each metal by oxygen atoms of borate and chloride ions. Magnetic susceptibility measurements of dinuclear complexes revealed that these exhibit antiferromagnetic coupling behavior due to the presence of two metal ions in close proximity. The nature of the metal complexes was confirmed by conductometric measurements; indicated that the complexes are 1:1 electrolytes. The antimicrobial activities of the ligand, as growth inhibiting agents, have been screened in vitro against several species of bacteria and plant pathogenic fungi. The antimicrobial data revealed that the metal complexes act more as bactericidal and fungicidal agents as compared to the ligand.
Keywords: Borate; Dinuclear complexes; Thermogravimetric analysis; Antimicrobial activity.