Why in news?

The 2025 Nobel Prize in Chemistry was awarded to Susumu Kitagawa, Richard Robson, and Omar Yaghi for developing metal–organic frameworks (MOFs) — intricate molecular structures with vast internal spaces that can host, store, or react with other molecules.

Their breakthrough transformed chemistry from merely creating individual molecules to designing three-dimensional frameworks, opening new possibilities in catalysis, gas storage, and material science.

What’s in Today’s Article?

• About Metal–Organic Frameworks (MOFs)
• How Robson and Kitagawa Pioneered Metal–Organic Frameworks
• Omar Yaghi’s Breakthrough: Building Strong and Reproducible MOFs
• Importance of Metal–Organic Frameworks (MOFs)

About Metal–Organic Frameworks (MOFs)

• Metal–Organic Frameworks (MOFs) are three-dimensional networks made of metal ions linked by organic molecules.
• These structures contain large, porous cavities through which gases and liquids can flow, making them extremely adaptable for diverse applications such as gas storage, filtration, and catalysis.
• How MOFs Are Built?
  • In a MOF, metal ions act as anchors or joints in a scaffold, while organic molecules serve as flexible linkers connecting them.
  • These organic linkers can form rings or chains and can be chemically tailored to give the framework specific properties, allowing fine control over structure and function.
• The Chemistry Behind the Design
  • At their core, MOFs are built on basic bonding principles — atoms form bonds to achieve stability, usually by completing eight electrons in their outer shell.
    • Atoms with fewer than four electrons tend to lose them.
    • Atoms with more than four try to gain electrons.
    • This process, determined by an element’s valency, governs how metal ions and organic molecules link together.
  • Carbon, the key element in organic compounds, can form stable rings and chains, enabling the creation of complex, customizable molecular frameworks that define MOFs.

How Robson and Kitagawa Pioneered Metal–Organic Frameworks?

• In the 1970s, Richard Robson of the University of Melbourne realised that the geometry of atomic connections could be scaled up to design larger molecular structures.
• In the 1980s, he combined copper ions (which bond tetrahedrally) with an organic molecule containing four nitrile arms, resulting in a diamond-like crystal lattice filled with porous cavities instead of dense atomic bonds.
• These frameworks could potentially trap ions, catalyse reactions, and filter molecules by size. However, Robson’s early structures were too fragile.
• Building on this idea, Susumu Kitagawa in Japan stabilised them, turning fragile lattices into functional porous materials.
• In 1997, he used cobalt, nickel, and zinc ions linked with 4,4’-bipyridine to create the first stable, three-dimensional MOF that allowed gases like methane, nitrogen, and oxygen to flow in and out without collapsing.
• Kitagawa also discovered that some MOFs could be soft and flexible, expanding, contracting, or bending based on temperature, pressure, or the type of molecules inside — a property that made MOFs practical and versatile for real-world applications.

Omar Yaghi’s Breakthrough: Building Strong and Reproducible MOFs

• In the 1990s, Omar Yaghi, working at Arizona State University, transformed metal–organic frameworks (MOFs) from fragile lab curiosities into strong, reproducible materials.
• Driven by a vision to design materials deliberately, Yaghi used metal ions as joints and organic molecules as struts to create extended, ordered structures.
• In 1995, he developed the first two-dimensional frameworks using cobalt and copper ions, which could hold guest molecules without collapsing.
• His major breakthrough came in 1999 with MOF-5, a three-dimensional lattice made from zinc ions and benzene-dicarboxylate linkers.
• It was thermally stable up to 300°C, and just a few grams had an internal surface area equal to a football field.

Importance of Metal–Organic Frameworks (MOFs)

• The appeal of metal–organic frameworks (MOFs) lies in:
  • their extraordinary internal surface area — a small amount of material can expose an immense surface for chemical interactions — and
  • their tuneable design, allowing chemists to customise them for countless applications.
• In environmental uses, MOFs like CALF-20 capture carbon dioxide from factory exhausts, while MOF-303 extracts drinking water from desert air, and UiO-67 removes PFAS pollutants from water.
  • MIL-101 and ZIF-8 accelerate pollutant breakdown and help recover rare-earth metals from wastewater.
• In the energy and industrial sectors, NU-1501 and MOF-177 store hydrogen and methane safely at moderate pressures for clean-fuel vehicles.
• Others are used to contain toxic gases or act as drug-delivery systems, releasing medicines in response to biological signals.
• Together, these applications show how MOFs combine scientific ingenuity with real-world impact, addressing key challenges in energy, environment, and health.