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.