Anomalies in the Kinetics of Substitution in [Os(NH3)5H2O]3+

The 57Fe Mossbauer spectrum of [RuIV(NH3)4(NH2)(FeII(CN)6H)] consists of a quadrupole doublet, showing that, in being formed in the reaction of [Ru(NH3)5H2O]3+ with Fe(CN)63-, the bridging ligand has undergone a rotation of 180°, consistent with there being an induction period in the reaction profile for its appearance. In harmony with the foregoing, [OsIV(NH3)4(NH2)(FeII(CN)6H)], the product of the analogous reaction, shows a single absorption peak, its appearance following a first-order reaction. Though an induction period is observed in the formation of [OsIII(NH3)5(FeII(CN)6)]-, the Mossbauer spectrum of the potassium salt shows a single absorption peak. Our present more detailed study of the kinetics of substitution by Fe(CN)64- and Co(CN)63- in [Os(NH3)5H2O]3+ in unacidified solution shows that a catalyst for the reaction of the former is generated by the residual O2 in a controlled-atmosphere box. The kinetic behavior of the reaction system with catalyst deliberately generated is described in this ...