Metal-organic frameworks, usually abbreviated MOFs, are porous crystals assembled from metal ions and long organic molecules. The metal ions act as cornerstones, while the carbon-based molecules connect them into an extended structure. Large cavities remain within the crystal, creating spaces through which gases and other chemicals can flow. This combination of solid architecture and internal room makes MOFs useful subjects for understanding how molecular structure can be designed around a particular chemical task.
What makes a framework porous?
The structure can be pictured as a network of corners and connecting links. Its cavities are part of the architecture, rather than simply gaps outside the material. Changing the building blocks changes the framework and can give it different properties. In its 2025 Chemistry prize announcement, the Royal Swedish Academy of Sciences explains that chemists can vary these components to make MOFs capture and store specific substances. It also describes frameworks that catalyse chemical reactions. For a learner, the important connection is between the choice of components, their arrangement and the resulting function.
From wooden models to open channels
The Nobel Committee's account of the field's development begins with Richard Robson's teaching models in 1974. Wooden balls represented atoms, and rods represented bonds. The holes for those rods needed specific positions because different atoms form bonds in particular ways. The model-making problem drew attention to how the directions of connections could determine a larger structure.
In 1989, Robson presented a framework in the Journal of the American Chemical Society. He combined positively charged copper ions with a four-armed molecule whose ends were attracted to the copper ions. The result was an ordered crystal with many cavities, but it was unstable and collapsed easily. The example showed the appeal of spacious molecular constructions while leaving stability as a problem to solve.
Susumu Kitagawa's group reached an important milestone in 1997. Using cobalt, nickel or zinc ions with 4,4′-bipyridine, the group made three-dimensional frameworks containing open channels. After one material was dried to remove its water, it remained stable and its spaces could be filled with gases. This moved the explanation beyond a drawing of an open network: the channels could remain available when their contents changed.
Flexibility and families of frameworks
In 1998, Kitagawa described a vision of flexible frameworks. The Nobel account contrasts their flexible molecular building blocks with zeolites, which are usually hard materials. Thinking about flexibility broadens the picture of a porous crystal. Its useful characteristics can involve how the structure behaves as well as how much empty space it contains.
Omar M. Yaghi presented MOF-5 in 1999. The material combined spacious cavities with stability: even when empty, it could be heated to 300°C without collapsing. The Nobel account illustrates its internal area by comparing a couple of grams with the area of a football pitch. The comparison concerns the area inside the material, helping explain why the interior of a small quantity can be significant for gas storage.
In papers published in 2002 and 2003, Yaghi demonstrated how frameworks could be modified systematically. Sixteen variants of MOF-5 had cavities larger or smaller than those of the initial material. Varying the molecular links produced a family with different properties. This is a useful example of rational materials design: a framework becomes a starting point for comparing related structures and their functions.
Uses built around the cavities
The Nobel Committee's examples of MOF applications show several ways to use this internal space. MOF-303 captures water vapour from desert air at night and releases water when heated by the morning sun. MIL-101 has large cavities and can store hydrogen or carbon dioxide. UiO-67 can absorb PFAS from water. These examples connect particular framework names with particular functions; the properties of one example should be considered in the context of that material.
The account also describes MOFs used by the electronics industry to contain toxic gases needed for semiconductor production. Companies are testing materials that capture carbon dioxide from factories and power stations. It notes that most MOF uses have so far been on a small scale, making scale an essential part of interpreting an application alongside its chemical principle.
Carbon capture also appears in IUPAC's 2025 emerging technologies selection, which names Direct Air Capture and Electrochemical Carbon Capture and Conversion. IUPAC places its selected technologies between initial discovery and full commercialization. This offers broader context for reading about capture methods and for asking how a promising materials concept progresses toward practical use.
The 2025 Nobel Prize
Susumu Kitagawa, Richard Robson and Omar M. Yaghi received the 2025 Nobel Prize in Chemistry for developing metal-organic frameworks. The Academy reports that chemists have since built tens of thousands of different MOFs. Their development links a simple structural idea to stable channels, flexible architectures and systematically varied families of materials. Studying these stages together shows how choosing molecular components and controlling their arrangement can create spaces with chemical functions.