Kinetics and mechanism of the ligand substitution reaction of [(H2O)(tap)2RuORu(tap)2(H2O)]2+ {tap = 2-(m-tolylazo)pyridine} with diethyldithiocarbamate anion in aqueous solution at pH 7.4
Description
Department of Chemistry, The University of Burdwan, Burdwan-713 104, West Bengal, India
E-mail : alakghosh2002@yahoo.co.in
Manuscript received online 02 August 2012, accepted 12 August 2012
Kinetic and mechanistic studies on the interaction of diethyldithiocarbamate anion [DDTC-] with the title complex at physiological pH and in aqueous medium have been done spectrophotometrically as a function of [(H2O)(tap)2RuORu(tap)2(H2O)2+], [DDTC-], pH and temperature at constant ionic strength. The interaction reaction followed two parallel paths : both the paths are dependent on [ligand] and showed a limiting nature at higher concentration of the ligand. Rate constants (k1 ~ 10-3 s-1 and k2~10-5 s-1), activation parameters (∆H1# = 14.14 ± 0.96 kJ moI-1, ∆S1# = -241.59 ± 2.93 JK-1 moI-1, ∆H2# = 31.88 ± 1.91 kJ moI-1, ∆S2# = -232.94 ± 5.79 JK-1 moI-1) were calculated. A rate law involving the outer sphere association complex formation has been established at pH 7.4 as
Rate = K1KE[{(H2O)(tap)2RuORu(tap)2(H2O)}2+][ligand]/(1 + KE[Iigand])
Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction processes. From the temperature dependence of the outer sphere association equilibrium constant, the thermodynamic parameters were also calculated, which gives a negative ∆G° value for both the paths at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex. The product of the reaction has been characterized, as IR and ESI-mass spectroscopic analysis.