Monohydraatins

Monohydraatins are a proposed class of hydrated inorganic compounds defined by incorporating one molecule of water per formula unit. In simple terms, they would have a general formula MX·H2O, where M is a metal cation and X represents an anion or coordinating ligand. The distinguishing feature is a single water of crystallization associated with each formula unit; this differentiates monohydraatins from dihydrates or polyhydrates.

Structure and bonding: Water molecules occupy specific lattice sites and participate in hydrogen-bonding networks, sometimes coordinating to the metal center. The water can be only weakly bound and lost upon heating or exposure to reduced humidity, or in framework structures it may be more tightly integrated into the network.

Formation and stability: Monohydraatins can be formed by controlled hydration of anhydrous salts or oxides under humid conditions, or by solvothermal synthesis. Their stability depends on the strength of the hydration interactions and the geometry of the crystal lattice; dehydration temperatures range widely from room temperature to several hundred degrees Celsius in different systems.

Properties and applications: Dehydration is usually reversible, allowing rehydration by exposing the material to water vapor. The concept has attracted interest for humidity sensing, selective sorption, and as a model system for studying water–solid interactions. In mainstream literature, however, the term is uncommon and many researchers simply refer to the corresponding monohydrates without using the broader class label.

See also: Monohydrate, Hydrate, Water of crystallization, Dehydration.