1. Complexation, definitions and nomenclature

1.1 Chemical bonds

All common types of chemical bond can be found in complexes. Purely ionic bonds, for example, require one of the two bonding partners to give up an electron to the other. When the electron is not fully surrendered by one partner to the other, this is referred to as a polar bond. However, these bonds do not explain the existence of molecules formed between identical atoms such as Cl ₂ or H ₂ . In 1916, Lewis discovered a third type of bond to explain the existence of such molecules. This is the covalent bond, which involves the sharing of two electrons. However, these types of bond do not explain the existence of many complex molecules. A first difficulty arises from the known...