The Mercury(II) Catalyzed Ligand Exchange Between Hexacyanoferrate(II) and Pyrazine in Aqueous Medium

• DOI: 10.1007/s11243-005-6266-6
• Publication Date: 2005-10-15T13:19:46Z
• Authors: Radhey M. Naik; Raj K. Tewari; Pradeep K. Singh; Anjani Tewari; Surendra Prasad
• Keywords: Pyrazine; Organometallic Chemistry

The kinetic and mechanistic studies of HgII catalyzed exchange of coordinated cyanide in hexacyanoferrate(II) by pyrazine (Pz) were monitored by following the appearance of the yellow complex [Fe(CN)5Pz]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 (KNO3). 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 HgII, the initial rates were determined at several concentrations of HgII, 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.