Kinetics of ligand exchange reactions of copper(II) complexes

Abstract

The kinetics of the reactions of the copper (II) complexes of pyridine-2-aldehyde-2′pyridylhydrazone (PAPHY) with ethylenediaminetetraacetic acid (EDTA) and triethylenetetramine (trien) have been studied at 25 °C and 0.1 ionic strength. the reaction is first order in copper complex and first order in the incoming ligand. The rate constant is pH dependent reaching a maximum at pH 7.5 and 9 for EDTA and trien respectively. The rate determining step in the reaction with trien is the loss of a water molecule from the CuPAPHY complexes. The rate determining step in the reaction with EDTA occurs after the coordination of the EDTA to the complex. The effect of deprotonation of the ligand in the copper complex on the rate of exchange of the coordinated water molecules is discussed.