By writing AB⋅xCD chemists mean that there are CDs are found in the crystalline framework of AB. The most common example of this is water trapped inside the crystal structure of ionic compounds.
An example that's often taught is CuSO4⋅5H2O. See that 5 that's a representative of x? It means that water can be bound only with intermolecular interactions, but it exists in the structure in a stoichiometric ratio.
The formula of the hydrated form is CuSO 4. 5H 2 O. The dot after the formula for copper sulphate indicates bonds with water molecules. Research suggests that the nature of these bonds is not as simple as was once thought.
