Multivariate Hydrogen-Bonded Organic Frameworks for Optimum Atmospheric Water Harvesting

Hydrogen-bonded organic frameworks (HOFs) offer atomic-precision platforms for probing water adsorption, yet monotonic building units often fail to meet the multifaceted demands of atmospheric water harvesting (AWH). In this study, a multivariate (MTV) strategy is employed to tune adsorption onset, work capacity, and cycling stability in HOFs. Introducing amino groups in controlled ratios creates a balance between hydrophilic sites and dynamic confinement within ordered frameworks. Specifically, the parent HOF, PFC-76, was constructed from the organic linker [1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (TPTCA), which assembles into 2D honeycomb networks via carboxylic acid dimer synthons. Functionalizing TPTCA with amino groups modulates the framework's packing and dynamic behavior. Single-crystal X-ray crystallography revealed sliding dynamics in PFC-76-NH₂ during water adsorption, along with ordered water arrangements within the dynamic confinement spaces. Systematic variation of amino content (50%, 67%, and 80%) generated an atactic distribution of functional groups while maintaining crystallinity and porosity. This compositional tuning enhanced H₂O uptake, optimized the adsorption inflection point, and delivered an outstanding cycling stability. The strategy demonstrates how precise control over functional group incorporation and framework dynamics can yield programmable performance in soft porous crystals for practical applications.