MECHANISTIC STUDIES ON LIGAND SUBSTITUTION IN HEXAAQUARHODIUM(II) IONBY SALICYLALDOXIME

The kinetics of formation of [Rh(OH2)(4)(salH)](2+) from [Rh(OH2)(6)]( 3+) has been studied spectrophotometrically by following the appearanc e of a characteristic peak of the product complex (lambda(max) = 345 n m) as a function of substrate and ligand concentrations, temperature a nd solvent polarity. The rate of the reaction is found to be first ord er each in [substrate] and [ligand]. Activation parameters (Delta H do uble dagger = 54.4 kJ mol(-1), Delta S not equivalent to = - 77.0 JK(- 1) mol(-1)), compared with that of the water-exchange, suggest an asso ciative mode of activation. Solvent effect study also helps to lead to the same mechanistic conclusion.