Kinetic studies of complexation reactions of water-soluble hydrazones with nickel(II) and palladium(II) ions

The kinetics of complexation reactions of five water-soluble heterocyclic hydrazones with nickel(II) and palladium(II) ions have been investigated by stopped-flow spectrophotometry. Rates of complexations with nickel(II) and palladium(II) in the absence of chloride ion were found to be proportional to the first order of the ligand and metal ion concentrations and to the inverse first order of the hydrogen ion concentration except for the complexation of alpha-(2-benzimidazolyl)-alpha-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic acid with palladium(II). Rates of complexation with palladium(II) in the presence of chloride ion were best described by a two-term expression, both terms being first order in the palladium ion and ligand concentrations and inverse first order in the hydrogen ion concentration. The first term has zero dependence of the chloride ion concentration, whereas the second is first order with respect to the chloride ion concentration. The rate constant for each complexation reaction was determined. The complexation of the hydrazones with nickel(II) was estimated to go according to an Eigen mechanism and that with palladium (II) according to the associative mechanism.