HKUST-1 arrived in Science in early 1999 from a Hong Kong team, and history has been slightly unfair to it: it is routinely mentioned second to MOF-5 despite preceding it and despite making an argument MOF-5 did not. Chui and colleagues did not only show permanent porosity in their copper trimesate lattice; they showed that the axial water molecules on each Cu2 paddlewheel could be removed and replaced, turning every metal node into an addressable chemical site.
That is the paper's lasting contribution. The 'chemically functionalizable' of the title means the framework interior behaves like a reagent, not a container. Dehydrated HKUST-1 presents open Cu(II) sites that bind CO2, water, ammonia and olefins with real selectivity, which is why the material became one of the first MOFs manufactured at commercial scale under the name Basolite C300.
The structure itself is elegant: paddlewheel dimers connected by benzene-1,3,5-tricarboxylate into a tbo net with intersecting channels of roughly 9 angstroms and a surface area around 1,800 m2/g. Synthesis is forgiving, crystals grow large, and the deep blue-to-turquoise color change on hydration gives an instant visual readout of pore occupancy that generations of students have used as their first MOF experiment.
Weaknesses are the mirror image of the strengths. The same open copper sites that bind guests so eagerly also bind water irreversibly under humid conditions, and HKUST-1 degrades noticeably in moist air, a limitation that took the field years to quantify honestly. The paper also predates modern activation protocols, so its reported uptakes undersell what optimized samples achieve. Still, as a founding document it holds up remarkably well: shorter, more chemically opinionated, and in some ways more prescient than its more famous zinc cousin.