KINETICS OF ELECTRON-TRANSFER REACTIONS OF MANGANESE(III) COMPLEXES OF TRANS-CYCLOHEXANE-1,2-DIAMINE,-NNN'N'-TETRAACETIC ACID AND 2,2'-BIPYRIDYL WITH ASCORBIC-ACID IN AQUEOUS ACID-MEDIA

The kinetics of the reactions of manganese(III) complexes of trans-cyclohexane-1,2-diamine-NNN'N'-tetraacetic acid (H4cydta) and 2,2'-bipyridyl (bpy) have been investigated in the acid ranges [H+] = 1.00 x 10(-5) - 3.16 x 10(-3) M and [H+] = 0.10 - 1.00 M, respectively, at different temperatures and at a constant ionic strength. Both the molecular and mono-anionic forms of ascorbic acid have been found to be reactive in the experimental acid ranges. The monoan-ionic species has been found to be more reactive than the molecular form. Attempts have been made to correlate the kinetic results in terms of the Marcus relationship for outer-sphere electron transfer reaction. Differences between the calculated rates (k0.s) and experimental rates (k) by approximately four and seven orders of magnitude (k0.s << k) suggest an innersphere pathway for the reaction of Mn(cydta)(H2O)-. Inner-sphere reaction is also believed to be operative for the other reaction. The activation parameters have been evaluated and compared with other reported systems.