KINETIC INVESTIGATION OF ELECTRON-TRANSFE R REACTION BETWEEN TRANS-[(EN)(2)(NO2)CO(O2CC5H5N)](2+) FE(II)/

trans - [(en)(2)(NO2)Co(O2CC5H5N)](2+) (ClO4)(2), which is first repor ted, has been synthesized and characterized by elemental analysis, UV - Vis and IR spectra, and X - ray structural analyses. Kinetic behavio urs of the Co(III) complex reduced by [Fe(CN)(6)](4-) and [Fe(CN)(5)(H 2O)](3-) have been investigated. The results indicated the electron tr ansfer (ET) reactions followed the outer-sphere mechanism or the inner -sphere mechanism respectively. At 25 degrees C, I = 0.50mol . L(-1), the ion-pair formation constant Q(ip) and ET rate constant k(et) of th e precursor complex for trans - [(en)(2)(NO2)Co(O2CC5H5N)](2+)/[Fe(CN) (6)](4-) are 29mol(-1). L and 2.4 x 10(-1) s(-1), the activation entha lpy Delta H-et(not equal) and the activation entropy Delta S-et(not eq ual) of this ET process are 1.2 x 10(2)kJ . mol(-1) and 5.0 x 10(2)kJ . mol(-1). K-1 respectively. The intramolecular ET rate constant of th e precursor binuclear complex for trans - [(en)(2)(NO2)Co(O2CC5H4N)]()/[Fe(CN)(5)(H2O)](3-) is 7.0 x 10(-5) s(-1) at 40 degrees C, pH = 8.0 and I = -0.10mol . L(-1). Finally the influence of the molecular orbi tal symmetry and the redox potentials on ET rate have been discussed.