Equilibrium constants for the pH-dependent axial ligation of alkyl(aquo)cobaloximes by pyridine and substituted pyridines

Department of Chemistry, Osmania University, Hyderabad-500 007, India E-mail : ssnsirsani@yahoo.com Manuscript received 23 September 2002, accepted 13 February 2003 Equilibria for the reaction of alkyl(aquo)cobaloximes (R = CH3, C2H5) with pyridine and substituted pyridines (4- methylpyridine, 4-ethylpyridine, 4-aminopyridine, 2-ethylpyridine and 2-aminopyridine) were studied as a function of pH at 25°, 1.0 M ionic strength (KCl) by spectrophotometric technique. Affinity of binding was interpreted based on the basicity of incoming ligand, steric effect and nature of alkyl group trans to H2O in cobaloxime. 2-Aminopyridine and 2-ethylpyridine binds to alkylcobaloxime very weakly due to the steric hindrance caused by the substituent at C2 of pyridine