pseudohydrates

Pseudohydrates are chemical species that resemble hydrates in their apparent water content or hydration behavior but do not contain water of crystallization in the conventional sense. The term has appeared in various branches of inorganic and solid-state chemistry, where researchers describe compounds that exhibit hydration-like properties without incorporating discrete water molecules as part of the crystal lattice.

In practice, a pseudohydrate may involve water-related features such as hydrogen-bond networks, dynamic water exchange, or water-like activity arising from hydroxyl groups or tightly bound lattice species. Water, when present, is not fixed as a crystal water of hydration, or could be displaced by other ligands while maintaining similar physical properties to a hydrated material. As a result, pseudohydrates can display reversible hydration–dehydration behavior, humidity sensitivity, and solubility patterns that resemble true hydrates, even though their microscopic structure differs from conventional hydrates or solvates.

Because the term is not standardized, its meaning can vary between authors. Some use pseudohydrate to describe coordination polymers or porous solids where water participates in hydrogen bonds or occupies cavities without acting as discrete, well-defined water ligands; others prefer explicit descriptions of water content, hydration number, and the identities of water or hydroxyl groups. The concept is primarily used descriptively, and modern discussions often favor precise structural or compositional terminology to avoid ambiguity.