Abstract
The kinetics of the mercury(II) catalysed ligand exchange of the hexacyanoferrate(II) complex with the N-methylpyrazinium ion (Mpz+) in a potassium hydrogen phthalate buffer medium has been investigated at 25.0 ± 0.1 °C, pH = 5.0 ± 0.02 and ionic strength, I = 0.1 M (KNO3). The reaction was followed spectrophotometrically in the aqueous medium by measuring the increase in absorbance of the intense blue complex [Fe(CN)5Mpz]2− at its λmax 655 nm. The effect of pH, and the concentrations of [Fe(CN)6 4−] and Mpz+ on the reaction rate have been studied and analysed. The varying catalytic activity of mercury(II) as a function of concentration has also been explained. The kinetic data suggest that substitution follows an interchange dissociative (I d) mechanism and occurs via formation of a solvent-bound intermediate. The effects of the dielectric constant of the medium on the reaction rates have been used to visualize the formation of a polar activated complex and an interchange dissociative mechanism for the reaction. A mechanism has been proposed in order to interpret the kinetic data. Kinetic evidence is reported for the displacement of CN− by Mpz+ in [Fe(CN)6 4−]. Activation parameters for the catalysed and uncatalysed reaction have been evaluated, and lend further support to the proposed mechanism.
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Prasad, S. Kinetics and mechanism of exchange of cyanide in hexacyanoferrate(II) by N-methylpyrazinium ion in the presence of mercury(II) as a catalyst. Transition Metal Chemistry 28, 1–8 (2003). https://doi.org/10.1023/A:1022501519744
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DOI: https://doi.org/10.1023/A:1022501519744