• S Satyanarayana

      Articles written in Journal of Chemical Sciences

    • Synthesis,13C and15N NMR and infrared studies of cyano(ligand) cobaloximes

      A Rajeshwar Rao S Satyanarayana

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      Mixed ligand complexes of [CNCo(D2H2)L] (whereL=imidazoles, benzimidazoles, thiourea or hydroxylamine) were prepared by treating the [CNCo(D2H2)SCN] with ‘L’ in alcohol. Imidazoles and benzimidazoles bind to Co(III) through N3, thiourea throughS and hydroxylamine throughN of NH2. The analogous series of complexes enriched in13C and15N of the cyanide ligand have been used to locate the cyanide’s13C and15N NMR resonances and the cyanide stretching frequencies in the infrared spectra. As thetrans axial ligand is varied, an inverse dependence of the15N chemical shift on the13C chemical shift is observed. This data together with trends inδ15N,δ13C andν CN with the basicity of thetrans axial ligand are interpreted to indicate that the cobalt to cyanideπ bonding is important in these cyano (ligand) complexes.

    • Coenzyme B12 model studies: An HSAB approach to the equilibria and kinetics of axial ligation of alkyl(aquo)-cobaloximes by imidazole and cyanide

      Vaddeboina Sridhar S Satyanarayana

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      Kinetics and equilibria of the axial ligation of alkyl(aquo)cobaloximes by imidazole and cyanide have been measured spectrophotometrically in aqueous solutions of ionic strength 1.0 M at 25°C as a function of pH. Comparison of KIMD and KCN- of CH3, C2H5 and BrCH2cobaloximes indicates that their stability is in the order BrCH2>CH3>C2H2. As the electron-withdrawing capacity of the alkyl grouptrans to water increases, the electron density of the cobalt(III) decreases and thus it becomes a stronger Lewis acid and binds more strongly to imidazole and cyanide. The association and dissociation rate constants are better correlated to the relative softness of the ligand showing that cyanide binds 30 times faster than imidazole. These complexes are isolated and are characterized by IR and1H NMR spectra.

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