Spectroscopic, redox and biological activities of transition metal complexes with ons donor macrocyclic ligand derived from semicarbazide and thiodiglycolic acid

A novel macrocyclic Schiff base ligand (2,5,9,12,14,18-hexaoxo-7,16-dithia-1,3,4,10,11,13-hexaazacycloocta-decane (H6L) with N4S2 coordinating sites was prepared by the reaction of the semicarbazide and thiodiglycolic acid. The transition metal complexes with macrocyclic ligand were synthesized and characterized by elemental analyses, magnetic susceptibility measurements, molar conductance, IR, electronic, and EPR spectral studies. Mass, H-1 NMR and IR spectral techniques suggest the structural features of macrocyclic ligand. Magnetic and electronic spectral studies suggest an octahedral geometry of complexes. Electrochemical behaviour of cobalt, nickel and copper complexes were determined by cyclic voltammetry. The cyclic voltammogram of the copper complex at room temperature shows a quasi-reversible peaks for Cu(III) --> Cu(II) and Cu(II) --> Cu(I) couples. The macrocyclic ligand and its complexes show growth inhibitory activity against pathogenic bacteria and plant pathogenic fungi A. niger, A. alternata and P variotii. Most of the complexes have higher activities than that of free ligand. (C) 2003 Elsevier B.V. All rights reserved.