配位化学双语课程

Lecture 5. Stability of Metal Complexes. Difference between Kinetic and Thermodynamic stability. Stepwise formation constants. Chelation and the Chelate Effect.

Stability, Chelation and the Chelate Effect

Introduction

A metal ion in solution does not exist in isolation, but in combination with ligands (such as solvent molecules or simple ions) or chelating groups, giving rise to complex ions or coordination compounds.

These complexes contain a central atom or ion, often a transition metal, and a cluster of ions or neutral molecules surrounding it. Many complexes are relatively unreactive species remaining unchanged throughout a sequence of chemical or physical operations and can often be isolated as stable solids or liquid compounds.

Other complexes have a much more transient existence and may exist only in solution or be highly reactive and easily converted to other species. All metals form complexes, although the extent of formation and nature of these depend very largely on the electronic structure of the metal. The concept of a metal complex originated in the work of Alfred Werner, who in 1913 was awarded the first Nobel Prize in Inorganic chemistry. A description of his life and the influence his work played in the development of coordination chemistry is given by G.B. Kauffman in "Inorganic Coordination Compounds", Heyden & Son Ltd, 1981.

Complexes may be non-ionic (neutral) or cationic or anionic, depending on the charges carried by the central metal ion and the coordinated groups. The total number of points of attachment to the central element is termed the coordination number and this can vary from 2 to greater than 12, but is usually 6.

The term ligand (ligare [Latin], to bind) was first used by Alfred Stock in 1916 in relation to silicon chemistry. The first use of the term in a British journal was by H. Irving and R.J.P. Williams in Nature, 1948, 162, 746.