An introduction to the complex ions formed by transition and other metals. Includes bonding, shapes and names, and a simple look at the origin of color. Looks in detail at various ligand exchange reactions and the chemistry of common hexaaqua ions. 8.3.1: Acidity of the Hexaaqua Ions This page explains why hexaaqua complex ions are acidic. 8.3.2: Geometry of Complex Ions This page describes the shapes of some common complex metal ions. It goes on to look at some simple examples of stereoisomerism (geometric and optical) in complex ions 8.3.3: Ligand Exchange Reactions (Introduction) This page describes some common ligand exchange (substitution) reactions involving complex metal ions. It assumes that you are familiar with basic ideas about complex ions. A ligand exchange reaction involves the substitution of one or more ligands in a complex ion with one or more different ligands. 8.3.4: Ligand Exchange Reactions (Thermodynamics) This page explains what is meant by a stability constant for a complex ion, and goes on to look at how its size is governed in part by the entropy change during a ligand exchange reaction. 8.3.5: Nomenclature of Complex Ions This page explains how to name some common complex metal ions. Although the names of complex ions can look long and worrying, the formulae are simply being coded in much the same way that organic names are coded. Once you have sorted out that code, the names are entirely descriptive. 8.3.6: Origin of Color in Complex Ions This page is going to take a simple look at the origin of color in complex ions - in particular, why so many transition metal ions are colored. 8.3.7: Reactions of the Hexaaqua Ions with Ammonia Reactions of the hexaaqua ions with ammonia solution are complicated by the fact that the ammonia can have two quite different functions. It can act as a base (in the Brønsted-Lowry sense), but it is also a possible ligand which can replace water molecules around the central metal ion. When it acts as a ligand, it is acting as a Lewis base. We need to look at these two functions separately. 8.3.8: Reactions of the Hexaaqua Ions with Carbonate Ions This page describes and explains the reactions between complex ions of the type [M(H₂O)₆]ⁿ⁺ and carbonate ions from, for example, sodium carbonate solution. There is a difference in the reactions depending on whether the metal at the center of the hexaaqua ion carries a 2+ or a 3+ charge. We need to look at each cases separately. 8.3.9: Reactions of the Hexaaqua Ions with Hydroxide Ions This page describes and explains the reactions between complex ions of the type [M(H2O)6]n+ and hydroxide ions from, for example, sodium hydroxide solution. It assumes that you know why these ions are acidic, and are happy about the equilibria involved. 8.3.10: Stereoisomerism in complex ions Some complex ions can show either optical or geometric isomerism.