Kinetic and Mechanistic Studies of the Interaction of Hydroxopentaaquarhodium(III) Ion with Potassium Hexacyanoferrate(III)

The substitution reaction of potassium hexacyanoferrate(III) with hydroxopentaaquarhodium(III) has been studied spectrophotometrically as a function of pH, [substrate] and [Fe(CN) 6 3 m ] by following the absorption of Fe(III) substituted product at 355 nm. The rate of the reaction increases with the increase in [Fe(CN) 6 3 m ] but decreases with the increase in [H + ] and ionic strength of the medium. The activation parameters, j H # (36.5, 42.5) kJ mol m 1 and j S # ( m 191.0, m 133.0)J K m 1 mol m 1 for k S and k f paths respectively, have been calculated form the Eyring plots and were compared with the aqua exchange and analogous ligand substitution reactions. j G 0 , j H 0 and j S 0 for the outer-sphere association ( K OS ) path have been calculated, both from kinetic as well as the experimentally obtained equilibrium constant values. The mechanistic pathway for the substitution reaction within the outer-sphere complex is consistent with an associative interchange (Ia) type of phenomenon.