ROLE OF LIGANDS ON THE REDUCING CAPABILITIES OF METAL COMPLEXES

Kinetic investigation of the reduction reaction of tris (1-10-orthophenanthroline) iron (III) complex with potassoium hexacyanoferrate (II), bis ( π -cyaclopentadienyl) iron (II), and ethylene iamminetetraacetateuranium (IV) complexes has been carried out. The rates of reduction have been explained in terms of free energy changes of the reaction and entropy of activation in connection with different theories of electron transfer processes. The findings of the study strongly support the provisions of molecular orbital theory, Marcus and electron tunneling theories for outer sphere electron transfer mechanism. Thermodynamics parameters Δ S # (J K-1 mol-1), Δ G # (kJ mol-1), Δ H # (kJ mol-1), and Δ Go (kJ mol-1), have been calculated and found to be -189, 64.01, 7.69, -76.14 respectively for the redox reaction between [Fe (o-phen)3]3+ and [Fe (CN)6]4-, -208, 66.45, 4.32, -72.08 respectively for the redox reaction between [Fe(o-phen) 3] 3+ and [Fe (C5H5)2], -235, 71.28, 1.25, -66.97 respectively for the redox reaction between [Fe (o-phen) 3] 3+ and [U (IV) EDTA]