Lamellar‐Type Crystals of an Amphiphilic Anilinium Chloride Adsorbing and Desorbing Water Vapor Under Mild Conditions

ABSTRACT

Organic ammonium halides, which are obtained by neutralizing organic amines with hydrogen halides, exhibit several properties and functions based on their diverse hydrogen bond networks. Here we report 2‐(2‐hydroxyethyl)anilinium chloride as a novel organic ammonium halide and describe its reversible hydration/dehydration behavior under mild conditions. Single‐crystal X‐ray diffraction analysis shows that this halide crystalizes into two different lamellar‐type crystals, anhydrate and monohydrate, composed of hydrophobic phenyl and hydrophilic hydrogen bonded layers. Powder X‐ray diffraction, thermogravimetric, and gas adsorption analyses indicate that the anhydrate crystals adsorb water vapor by incorporating water molecules into their hydrophilic layers under atmospheric humidity, and the monohydrate crystals readily desorb water by mild heating at approximately 50°C for several minutes. Notably, these hydration and dehydration processes are reversible with crystal‐to‐crystal transformation. Therefore, 2‐(2‐hydroxyethyl)anilinium chloride can be utilized as an excellent water vapor adsorber, opening up the potential for organic ammonium halides, particularly anilinium halide frameworks, as a functional crystalline material.