KINETICS AND EQUILIBRIUM-CONSTANTS OF SOME PENTACYANOFERRATE(II) COMPLEXES OF NITROGEN AND SULFUR-CONTAINING HETEROCYCLES

The kinetics of the substitution reactions of Fe(CN)(5)H(2)O(3-)ion wi th a series of nitrogen and sulfur containing heterocycles were studie d in aqueous media. In the presence of excess ligand, varied over a la rge range of concentrations, second-order rate constants were calculat ed at mu = 0.100 M NaClO4. Activation parameters for the formation rea ctions were found, Delta H and Delta S*, 28 +/- 6 kJ/mol and 135 +/- 20 J/mol, respectively. The results are interpreted as being consisten t with dissociative, SN1 mechanism. The kinetics of formation and diss ociation were studied by stopped-flow technique at several temperature s. An investigation of the kinetics of exchange of coordinated heteroc ycles for 1,3,5-triazine, yielded rate saturation that is typical of a limiting SN1 mechanism. Activation parameters of the limiting first-o rder specific rate of dissociations were found with Delta H and Delta S 53 +/- 2 kJ/mol and 105 +/- 5 J/mol, respectively. From the specif ic rates of formation and dissociation reactions the equilibrium const ants were calculated. (C) 1998 John Wiley & Sons, Inc.