Kinetics and mechanisms of substitution of aqua ligands from cis-diaquo-bis[2-(m-tolylazo)pyridine]ruthenium(II) by 8-hydroxy- quinoline in ethanol—water mixtures

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The kinetics of aqua ligand substitution from cis-[Ru-(tap)2(H2O)2]2+ (tap = 2-[m-tolylazo]pyridine) by 8-hydroxyquinoline (oxine) have been studied spectro-photometrically in various water-ethanol mixtures at different temperatures (30–45° C). The following rate law has been established in the pH range 4.5 to 6.5; $$ {⤪ d[(2)]/dt=k_{1}k_{2}[(1)][L]/(k_{-1}+k_{2}[L])} $$ where (1), (2) and L represent ds-[Ru(tap)2(H2O)2]2+, [Ru(tap)2(oxine)]2+ and oxine respectively. k1 is the water dissociation rate constant of (1); k−1 is the aquation rate constant and k2 is the oxine capturing rate of the pentacoordinate intermediate, [Ru(tap)2(H2O)]2+. Ionic strength has very little effect on the rate constants. The rate increases with the increase in pH. The experimental results are consistent with a dissociative mechanism.