Studies of Ruthenium Complexes. III. Kinetics of Isotopic Ligand-Exchange Reactions of Halogenopentaammineruthenium(III) Complexes in Aqueous Solution

Kinetic studies of isotopic ligand-exchange reactions, [Ru(NH3)5X]2++X*−=[Ru(NH3)5X*]2++X−, where X=Cl, Br, and I, have been made in aqueous solutions. The effects of the hydrogen- and halide-ion concentrations, and of the ionic strength of the aqueous solution on the exchange rate had not been observed under certain definite experimental conditions. The rate constants were determined to be 3.15×10−4 sec−1 for the chloro-pentaammine 3.63×10−4 sec−1 for the bromopentaammine, and 1.1×10−4 sec−1 for the iodopentaammine at 80°C. The energies of activation were 20 kcal/mol (chloropentaammine), 23 kcal/mol (bromopentaamine), and 30 kcal/mol (iodopentaammine). The reactions proceed through the following two steps: [Ru(NH3)5X]2++H2O→[Ru(NH3)5H2O]3++X− [Ru(NH3)5H2O]3++X*−→[Ru(NH3)5X*]2++H2O The first step is regarded as the rate-determining one.