Abstract
The kinetics of oxidation of the ternary complexes [Co-II(ADA)(Su)(H2O)](2-) and [Co-II(ADA)(Ma)(H2O)](2-) (ADA = N-(2-acetamido)iminodiacetate, Su = succinate and Ma = maleate) by periodate have been investigated spectrophotometrically at 580 nm under pseudo-first-order conditions in aqueous medium over 30-50 A degrees C range, pH 3.72-4.99, and I = 0.2 mol dm(-3). The kinetics of the oxidation of [Co-II(ADA)(Su)(H2O)](2-) obeyed the rate law d[Co-III]/dt = [Co-II(ADA)(Su)(H2O)](2-)[H5IO6] {k (4) K (5) + (k (5) K (6) K (2)/[H+)}, and the kinetics oxidation of [Co-II(ADA)(Ma)(H2O)](2-) obeyed the rate law d[Co-III]/dt = k (1) K (2)[Co-II] (T) [I-VII] (T) /{1 + ([H+]/K (7)) + K (2)[I-VII] (T) }. The pseudo-first-order rate constant, k (obs), increased with increasing pH, indicating that the hydroxo form of maleate complex, [Co-II(ADA)(Ma)(OH)](3-), is the reactive species. The initial Co(III) products were slowly converted to the final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters were calculated using the transition state theory equation. The initial cobalt(II) complexes were characterized by physicochemical and spectroscopic methods.