Synthesis, characterization, and mechanism of trans-dichlorido-bis-(ethylenediamine)cobalt(III) with L-cystine in the presence of chloride

Substitution reactions of trans-[CoCl2(en)(2)]Cl (where en = ethylenediamine) with L-cystine has been studied in 1.0 x 10(-1) mol dm(-3) aqueous perchlorate at various temperatures (303-323 K) and pH (4.45-3.30) using UV-Vis spectrophotometer on various [Cl-] from 0.05 to 0.01 mol L-1. The products have been characterized by their physico-chemical and spectroscopic data. Trans-[CoCl(en)(2)(H2O)](2+), from the hydrolysis of trans-[CoCl2(en)(2)](+) in the presence of Cl-, formed a complex with L-cystine at all temperatures in 1 : 1 molar ratio. L-cystine is bidentate to Co(III) through Co-N and Co-S bonds. Product formation and reversible reaction rate constants have been evaluated. The rate constants for SNi mechanism have been evaluated and activation parameters E-a, Delta H-#, and Delta S-# are determined.