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

Abstract

Substitution reactions of trans-[CoCl2(en)2]Cl (where en = ethylenediamine) with L-cystine has been studied in 1.0 × 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, ΔH #, and ΔS # are determined.