pseudohydrate

A pseudohydrate is a crystalline solid that contains a variable amount of water molecules within its structure, but not in a fixed stoichiometric ratio like a true hydrate. Unlike true hydrates, where water molecules are incorporated into the crystal lattice in specific, repeating arrangements and are often essential for the compound's stability and properties, pseudohydrates have a more loosely associated water content. The water in pseudohydrates can often be removed by drying at relatively low temperatures without fundamentally altering the crystalline structure of the anhydrous compound. This contrasts with true hydrates, where dehydration can lead to a significant structural transformation and a change in physical properties.

The term pseudohydrate is sometimes used to describe substances that appear to be hydrates but do not fit the strict definition. This can occur when a compound absorbs atmospheric moisture or traps water during crystallization in a way that is not a regular incorporation into the lattice. The amount of water in a pseudohydrate can vary depending on the environmental conditions, such as humidity and temperature. These compounds are generally less stable than true hydrates.