Ligand Exchange and Stability of Copper(II) Complexes

Abstract

The purpose of this study is to synthesize a series of copper(II) complexes and investigate the stability of copper(II) complexes which are tetra-ammine copper(II) sulphate and bis-ethylenediamine copper(II) sulphate by using copper(II) sulphate pentahydrate as the starting material. The synthesized products were characterized and identified by melting point, Fourier transforms infrared (FTIR) spectrophotometer, and UV-Visible (UV-Vis) spectroscopy. The stability constant of these copper(II) complexes were determined by using the electrochemical cell layout. In general, the greater the positive charge density on the central ion, the greater is the stability of its complexes. To find the stability is based on the chelate effect of the compound. Chelation is a type of bonding of ions and molecules to metal ions. The chelate effect can be seen by comparing the reaction of a chelating agent and a metal ion with the corresponding reaction involving comparable monodentate ligands. It has been known for many years that a comparison of this type always shows that the complex resulting from coordination with the chelating ligand is much more thermodynamically stable. This can be seen by looking at the values of stability constant for adding two monodentate ligands compared with adding one bidentate ligand. A monodentate ligand has only one donor atom used to bond to the central metal atom or ion while bidentate ligands, are Lewis bases that donate two pairs of electrons to a metal atom and are often referred to as chelating ligands. From this study, it shows that ethylenediamine is a chelating ligand that is more stable compared to ammine. Therefore, the stability constant value for ethylenediamine is smaller than ammine.