Kinetics and mechanism of the interaction of pyridine-2-thiol with <i>cis</i>-diaqua(ethylenediamine) platinum(II) perchlorate in aqueous medium

Abstract

The kinetics of the interaction ofpyridine-2- thiol with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺,[pyridine -2-thiol] and temperature at a particular <i>p</i>H<i> </i>(4.0) where the substrate complex exists predominantly as the diaqua species and pyridine -2-thiol as the neutral molecule. The reaction proceeds via a rapid outersphere association followed by two slow consecutive steps, having first order dependence on the aqua ion and pyridine-2-thiol in the second stage. Activation parameters have been calculated using Eyring equation .The low Δ<i>H</i>₁<i>^≠ </i>(36.0 ± 3.0 kJ mol^-1) and large negative value of Δ<i>S</i>₁<i>^≠</i> (- (1.66 ± 0.08) × 10² J K^-1 mol^-1) as well as Δ<i>H</i>₂<i>^≠</i> (26.0± 1.0 kJ mol^-1) and Δ<i>S</i>₂<i>^≠</i> (-(2.18±. 0.04) × 10² J K^-1 mol^-1) indicate associative mode of activation for both the aqua ligand substitution process in the two consecutive steps.