Sorting Out the Salts

There are two distinct types of coordination compounds separated from one another by their reactivity, which is due to the nature of the bonding from the metal to the ligand. Complex compounds are bound by coordinate covalent bonds described by valence bond theory (see Chapter 6). Addition salts or double salts, however, are bound according to electrostatic interactions, or ionic bonds. (Turn to Chapter 8 for details on ionic bonds and salts.) 

A double salt compound is stable in a solid state, but dissociates, or dissolves, into ions in an aqueous environment. They are called double salts because they are usually composed of two metal elements. (See Chapter 8 for details on the solubility of salts.) Complex compounds are also stable in solid state, but when added to an aqueous solution they maintain their structure rather than dissolving into ions. The addition salts or double salts also typically have lower coordination numbers than the complex compounds. 

Understanding the difference between the two types of coordination compounds is useful for various chemistry applications. The addition salts can be used to separate other materials from a solution. When the ions of a salt are dissolved into solution, they can bind to another ligand in the solution, forming an insoluble compound that precipitates out of solution. 

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