Hydration/Dehydration Induced Reversible Transformation between a Porous Hydrogen-Bonded Organic Framework and a Nonporous Molecular Crystal for Highly Efficient Gas Dehydration

Gas dehydration is a critical process in gas transportation and chemical reactions, yet traditional drying agents require an energy-intensive dehydration and regeneration step. Here, we present a nonporous molecular crystal called Melem that can be synthesized and scaled up through solid-state synthesis methods. Melem exhibits exceptional water selectivity in gas dehydration and can be reactivated under moderate conditions. According to the single-crystal structure and powder X-ray diffraction studies, a reversible structural transformation between Melem and its hydrated form, Melem–H₂O, induced by hydration/dehydration processes has been observed. Melem displays water adsorption properties with a maximum uptake of 11 mmol·g^–1 at p/p₀ = 0.92 and 298 K. Additionally, Melem retained consistent water capture capacities after 5 adsorption–desorption cycles. The remarkable gas dehydration performance of Melem was confirmed by column breakthrough experiments, which achieved a separation factor of up to 654.