Isostructural Transformation From a Hydrogen‐Bonded Metal‐Complex Framework to a Metal–Organic Framework for Enhanced Ammonia Tolerance

ABSTRACT Metal–organic frameworks (MOFs) are promising sorbents for ammonia (NH 3 ) storage and capture. However, rationally synthesizing target MOFs with NH 3 tolerance and reversible uptake still remains challenging. Here, we present a hydrogen‐bonded metal‐complex framework (ALP‐HOF‐1) that can isostructurally transform to a porous MOF (ALP‐MOF‐4) via a ligand substitution strategy to dramatically enhance NH 3 tolerance and reversibility. The remarkable NH 3 tolerance was unambiguously confirmed by the retention of NH 3 adsorption capacities after consecutive adsorption/desorption cycles and breakthrough experiments. At 298 K and 1.0 bar, ALP‐MOF‐4 exhibits a high NH 3 packing density comparable to liquid NH 3 . X−ray photoelectron spectroscopy and computational studies ascertain the binding domains of adsorbed NH 3 molecules. Open metal sites, Brønsted basic carbonyl (─C═O), and acidic ─NH groups in ALP‐MOF‐4 act cooperatively as preferred anchoring sites for NH 3 capture, resulting in excellent trace NH 3 capture performance under mixed NH 3 , CO 2 , and N 2 streams with effluent NH 3 below 50 ppm. The structural integrity and recyclability of ALP‐MOF‐4 demonstrate its potential as a durable NH 3 sorbent. This work provides design principles for rational transformations from HOFs to MOFs featuring active‐site environments for selective gas capture.