Transition metal complexes with N, S donor ligands as synthetic antioxidants: synthesis, characterization and antioxidant activity.

ABSTRACT

Transition metal complexes containing bidentate N, S donor ligands i.e., carvone thiosemicarbazone [(RS)-5-isopropenyl-2-methylcyclohex-2-en-1-one thiosemicarbazone (IPMCHTSC)] and carvone N(1)-phenylthiosemicarbazone [(RS)-5-isopropenyl-2-methylcyclohex-2-en-1-one phenylthiosemicarbazone (IPMCHPhTSC)] have been synthesized. All the metal complexes (1-8) have been characterized by elemental analysis, molar conductance measurement and various spectral studies [infrared (IR), electronic, fast-atom bombardment (FAB) mass and NMR (for ligands)] and thermogravimetric analysis. FAB mass spectroscopic studies of (1), (3), (4), (5), (6) (7), and (8) suggest their monomeric nature. Metal complexes are [M(LH)Cl(2)] and [M(LH)(2)Cl(2)] type, where M = Fe(III), Co(II), and Cu(II) and LH = IPMCHTSC and IPMCHPhTSC. The proposed geometries of the complexes were octahedral for 12 complexes, square planar for 11 complexes and distorted octahedral for Cu(II) complexes (12). The free radical scavenging activity of ligands (IPMCHTSC and IPMCHPhTSC) and their metal complexes have been determined at the concentration range of 10-400 µg/mL by means of their interaction with the stable free radical 2,2'-diphenyl-1-picrylhydrazyl and 5-200 µg/mL by 2,2'-Azinobis-3-ethylbenzothiazoline-6-sulphonic acid. All the compounds have shown encouraging antioxidant activities.