When Polymorphism in Metal–Organic Frameworks Enables Water Sorption Profile Tunability for Enhancing Heat Allocation and Water Harvesting Performance

Abstract The development of thermally driven water‐sorption‐based technologies relies on high‐performing water vapor adsorbents. Here, polymorphism in Al–metal–organic frameworks is disclosed as a new strategy to tune the hydrophilicity of MOFs. This involves the formation of MOFs built from chains of either trans‐ or cis‐ µ‐OH‐connected corner‐sharing AlO₄(OH)₂ octahedra. Specifically, [Al(OH)(muc)] or MIP‐211, is made of trans, trans‐muconate linkers, and cis‐µ‐OH‐connected corner‐sharing AlO₄(OH)₂ octahedra giving a 3D network with sinusoidal channels. The polymorph MIL‐53‐muc has a tiny change in the chain structure that results in a shift of the step position of the water isotherm from P/P₀ ≈ 0.5 in MIL‐53‐muc, to P/P₀ ≈ 0.3 in MIP‐211. Solid‐state NMR and Grand Canonical Monte Carlo reveal that the adsorption occurs initially between two hydroxyl groups of the chains, favored by the cis‐positioning in MIP‐211, resulting in a more hydrophilic behavior. Finally, theoretical evaluations show that MIP‐211 would allow achieving a coefficient of performance for cooling (COPc) of 0.63 with an ultralow driving temperature of 60 °C, outperforming benchmark sorbents for small temperature lifts. Combined with its high stability, easy regeneration, huge water uptake capacity, green synthesis, MIP‐211 is among the best adsorbents for adsorption‐driven air conditioning and water harvesting from the air.