MOF history is often told as a single lineage, which is unfair to Kyoto. Kitagawa's group had demonstrated gas adsorption in coordination polymers in 1997, and this sweeping 2004 review codified their distinct philosophy: porous coordination polymers classified into three generations, frameworks that collapse on guest removal, frameworks that stand rigid, and, the school's signature, third-generation frameworks that transform reversibly in response to guests, pressure or light.
That third category, later branded soft porous crystals, is the review's enduring gift. Gate-opening adsorption, breathing transitions, and stimulus-responsive pores are all sketched here as design goals rather than curiosities, complete with the coordination-chemistry logic, pillared layers, interdigitated grids, flexible ligand joints, for achieving each. An impressive fraction of what the field now studies under 'flexible MOFs' and 'stimuli-responsive materials' appears in this text in recognizable form.
As criticism: the review's classification is cleaner than reality, and some materials wander between generations depending on activation history, a nuance that hardened into taxonomy debates the field still has. The functional applications proposed, sensing, selective sorption via gate effects, took another decade to produce quantitative champions, so a 2004 reader could reasonably have accused the program of promissory notes.
The 2025 Nobel Prize, shared by Kitagawa alongside Robson and Yaghi, settled the historiography: there were two founding schools, one preaching rigidity and predictability, one preaching softness and responsiveness, and modern MOF science is their merger. This review is the cleanest single document of the second school, and it reads today as remarkably far-sighted.