<i>In Situ</i> Single-Crystal X-ray Diffraction Determinations of Cooperative Ammonia Capture in a Metal–Organic Framework

Porous metal–organic frameworks (MOFs) are promising sorbents for ammonia (NH 3 ) storage and capture; however, precisely defining the roles of active sites and establishing atomic-level insight into NH 3 binding domains remain challenging. Here, we report a robust zinc–allopurinol–imidazole framework, ALP-MOF-3, exhibiting exceptional thermal stability and tolerance to corrosive NH 3 . Using in situ single-crystal X-ray diffraction (SCXRD), complemented by Fourier-transform infrared (FT-IR) spectroscopy and computational analysis, we directly resolve the binding domains of adsorbed NH 3 molecules. The results reveal that open Zn(II) sites, in concert with Brønsted basic carbonyl and pyrimidine nitrogen functionalities, act cooperatively as strong anchoring sites for NH 3 . This synergistic capture enables energy-efficient uptake of trace NH 3 (1000 ppm) under both dry and humid (30–80% RH) conditions. The excellent structural integrity and recyclability of ALP-MOF-3 highlight its potential as a durable NH 3 sorbent and provide design principles for next generation MOFs with tailored active-site environments for selective gas capture.