The kinetic and mechanistic studies of Hg II catalyzed exchange of coordinated cyanide in hexacyanoferrate(II) by pyrazine (Pz) were monitored by following the appearance of the yellow complex [Fe(CN) 5 Pz] 3) at 440 nm corresponding to metal ligand charge transfer (MLCT) transitions at temp=25.0±0.1°C, pH=2.5±0.02 and ionic strength, I=0.1 M (KNO 3 ). The effect of pH, ionic strength and the concentrations of [Fe(CN) 6 ] 4) and Pz on the rate of reaction were also studied and explained. To investigate the dependency of catalytic activity of Hg II , the initial rates were determined at several concentrations of Hg II , keeping the concentration of other reactants constant. The kinetic observations suggest that the substitution follows an interchange dissociative (I d ) mechanism and proceeds via formation of a solvent-bound intermediate. The repetitive spectral scan is also provided as evidence for the exchange of cyanide ions by pyrazine in [Fe(CN) 6 ] 4) . Activation parameters have also been evaluated and provided support for the proposed mechanistic scheme.

The kinetics of Hg(II)-catalyzed reaction between hexacyanoferrate(II) and nitroso-R-salt has been followed spectrophotometrically by monitoring the increase in absorbance at 720 nm, the λ max of green complex, [Fe(CN) 5 N-R-salt] 3− as a function of pH, ionic strength, temperature, concentration of reactants, and the catalyst. In this reaction, the coordinated cyanide ion in hexacyanoferrate(II) gets replaced by incoming N-R-salt under the following specified reaction conditions: temperature = 25 ± 0.1 • C, pH = 6.5 ± 0.2, and I = 0.1 M (KNO 3 ). The stoichiometry of the complex has been established as 1:1 by mole ratio method. The rate of catalyzed reaction is slow at low pH values and then increases with pH and attains a maximum value between 6.5 and 6.7. The rate finally falls again at higher pH values due to nonavailability of [H + ] ions needed to regenerate the catalytic species. The rate of reaction increases initially with [N-R-salt] and attains a maximum value and then levels off at higher [N-R-salt]. The rate of reaction shows a variable order dependence in [Fe(CN) 6 4− ] ranging from unity at lower concentration to 0.1 at higher concentrations. The effect of [Hg 2+ ] on the reaction rate shows a complex behavior and the same has been explained in detail. The activation parameters for the catalyzed reactions have been evaluated. A most plausible mechanistic scheme has been proposed based on the experimental observations. C 2005 Wiley Periodicals, Inc. Int J Chem Kinet

The kinetics and mechanism of Hg 2+ -catalyzed substitution of cyanide ion in an octahedral hexacyanoruthenate(II) complex by nitroso-R-salt have been studied spectrophotometrically at 525 nm (λ max of the purple-red-colored complex). The reaction conditions were: temperature = 45.0 ± 0.1 • C, pH = 7.00 ± 0.02, and ionic strength (I) = 0.1 M (KCl). The reaction exhibited a first-order dependence on [nitroso-R-salt] and a variable order dependence on [Ru(CN) 6 4− ]. The initial rates were obtained from slopes of absorbance versus time plots. The rate of reaction was found to initially increase linearly with [nitroso-R-salt], and finally decrease at [nitroso-R-salt] = 3.50 × 10 −4 M. The effects of variation of pH, ionic strength, concentration of catalyst, and temperature on the reaction rate were also studied and explained in detail. The values of k 2 and activation parameters for catalyzed reaction were found to be 7.68 × 10 −4 s −1 and E a = 49.56 ± 0.091 kJ mol −1 , H = = 46.91 ± 0.036 kJ mol −1 , S = = −234.13 ± 1.12 J K −1 mol −1 , respectively. These activation parameters along with other experimental observations supported the solvent assisted interchange dissociative (I d ) mechanism for the reaction.

The complex process of nanoparticle formation in an aqueous solution is governed by kinetics and thermodynamic factors. This paper describes a room-temperature growth kinetic study and evaluation of thermodynamic activation parameters of monodispersed silver nanoparticles (AgNPs) synthesized in alkaline medium by chemical reduction method using AgNO 3 as a source of Ag + ions and tannic acid (TA) as a reductant (reducing agent) as well as a capping or stabilizing agent in the absence of any other external stabilizer. A simple and conveniently handled reaction process was monitored spectrophotometrically to study the growth kinetics in an aqueous solution as a function of the concentration of silver ion, hydroxide ion, and TA, respectively. The neutral nucleophilic group donates the electron density via a lone pair of electrons to Ag + ions for the reduction process, i.e., for the nucleation of AgNPs colloid. Also, a few silver ions form a silver oxide, which also facilitates the nucleation center to enhance the growth of AgNPs colloid. The decrease and increase in rate constant on varying the TA concentration showed its adsorption onto the surface of metallic AgNPs and stabilized by polygalloyl units of TA and were the main elements to control the growth kinetics. Consequently, stabilized TA-mediated AgNPs are formed using the electron donated by quinone form of TA followed by a pseudo-first-order reaction. Apart from this, nanoparticles formed were characterized using UV–visible spectrophotometry, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and powder X-ray diffraction techniques to confirm its formation during the present kinetic study.

5 PhNHNH 2 ] formed during the course of reaction has been found to be 1:1 using the mole ratio method. The evaluated values of activation parameters for the catalyzed reaction are E a = 53.85 kJ mol −1 , H = = 51.33 kJ mol −1 , and S = = −134.63 J K −1 mol −1 , which suggest an interchange dissociative mechanism. A most plausible mechanistic scheme has been proposed based on the experimental observations.