Reactivity of dichloro-(1,10-phenanthroline)gold(III) chloride towards sulfite in phen-phenH+ buffer medium

Department of Chemistry, St. Paul’s Cathedral Mission College, 33/1, Raja Rammohan Roy Sarani, Kolkata-700 009, India E-mail : palbiswajit@yahoo.com Department of Chemistry, Jadavpur University, Kolkata-700 032, India Manuscript received 08 August 2017, accepted 21 August 2017 The reactivity of dichloro-(1,10-phenanthroline)gold(III) chloride towards sulfite has been studied spectrophotometrically in phen-phenH+ buffer medium in the temperature range of 288 K to 303 K. The reaction between [Au(phen)Cl2 ]+ and HSO3– in phen-phenH+ buffer medium shows 1 : 1 stoichiometry. The reaction exhibits first order dependence on [{Au(phen)Cl2 }Cl] and less than unit order dependence on [HSO3–]. Phenanthroline has a retarding effect on the reaction rate. The variation in H+ concentration did not affect the rate of the reaction significantly. The reaction obeys the following rate expression. \(-{d[Au^{III}]_t \over dt} = {kK[Au^{III}]_t [HSO_3^-] \over [phen] + K[HSO_3^-]}\) (1) The pseudo-first order rate constant decreases with the increase in ionic strength, while the reaction rate increases with the decrease in dielectric constant of the medium. The reaction possibly involved a one step two electron transfer process to produce \(AuCl_2^-\) and SO42– as the reaction products of the respective reactants. A probable mechanism in conformity with the experimental observations has been suggested. The thermodynamic and the activation parameters were calculated with respect to the equilibrium step and the slow step of the reaction mechanism respectively