For generations, chemists have treated the Irving-Williams series as a fixed law of nature — copper, by virtue of its atomic structure, simply bonds more strongly than its neighbors. A team at KAIST in South Korea has now shown that this hierarchy is not destiny but circumstance, demonstrating in September 2026 that by reshaping the hydrogen bonds surrounding a copper complex rather than the metal bonds themselves, copper's dominance can be dismantled entirely. The finding suggests that stability in chemistry, as in so many domains of life, is less a property of the thing itself than of the en
KAIST Team Overturns Copper's Stability Dominance Using Hydrogen Bonding
Copper lost its throne not by changing, but by being held still.
Mark
So they didn't change the copper itself. They changed what was around it.
Mimi
Exactly. The hydrogen bonds in the outer sphere. Weak forces, but they constrained copper's ability to reshape itself into its preferred geometry.
Luke
And that's the key claim—that copper normally distorts its bonding structure to stabilize itself more, and the hydrogen bonds prevented that?
Mimi
Yes. The team kept the direct metal coordination identical across all six metals, so hydrogen bonding was the only variable.
Mark
Which means they could isolate its effect.
Mimi
Right. And it was enough to flip the entire Irving-Williams hierarchy.
Luke
But this is one system, one set of flavin derivatives. Does this principle generalize to other ligands, other environments?
Mimi
The paper doesn't claim universal application. It demonstrates the principle works in this specific case.
Mark
What's the practical payoff? Why does this matter outside the lab?
Mimi
Metal separation and recovery. If you can make one metal bond preferentially in a mixture, you can extract it selectively. And catalyst design—tuning the environment to favor one metal's reactivity.
Luke
Those are the stated applications. But has anyone actually built a working separation system based on this yet?
Mimi
Not yet. This is proof of concept. The next step would be engineering that into a real process.
Mark
So we're watching the beginning of something.
Mimi
We're watching the moment someone showed the door was open.
El Pulso
- A cornerstone assumption of coordination chemistry — that copper always wins the stability contest among transition metals — has been overturned by researchers manipulating forces once considered peripheral to the outcome.
- The disruption is conceptual as much as experimental: if metal stability can be rewritten by its surrounding environment, then decades of catalyst and separation design built on fixed hierarchies must be reconsidered.
- The KAIST team used flavin-based ligands derived from vitamin B2 to lock copper into a geometry it would naturally escape, stripping it of the structural flexibility that normally gives it its edge.
- Presented at the International Conference on Coordination Chemistry in Denmark — where first author Haneul Im won the Best Poster Award — and published in JACS on September 3, 2026, the work is moving from theoretical provocation toward practical application.
- The principle now offers chemists a design template for selectively extracting specific metals from mixtures and for building biomimetic catalysts that replicate how living cells choose which metal to recruit.
For generations, chemists have treated the Irving-Williams series as a fixed law of nature — copper, by virtue of its atomic structure, simply bonds more strongly than its neighbors. A team at KAIST in South Korea has now shown that this hierarchy is not destiny but circumstance, demonstrating in September 2026 that by reshaping the hydrogen bonds surrounding a copper complex rather than the metal bonds themselves, copper's dominance can be dismantled entirely. The finding suggests that stability in chemistry, as in so many domains of life, is less a property of the thing itself than of the environment it inhabits.
For decades, copper has sat at the top of the Irving-Williams series — the established ranking of how strongly transition metals bond with surrounding molecules. The series has been treated as an immutable consequence of atomic structure: change the metal, change the stability. That was the rule.
In early September 2026, a team at KAIST in South Korea published work that quietly dismantled it. Led by Professor Yunjung Baek, the researchers didn't swap out the copper or redesign the molecules gripping it directly. Instead, they tuned the hydrogen bonds in the outer environment — weak, peripheral forces — and copper fell from its position at the top.
The experiment centered on flavin, a compound found in vitamin B2. The team placed a series of transition metals into identical geometric arrangements built from flavin derivatives, varying only the hydrogen bonding in the outer shell. What they found was that copper, for all its electronic sophistication, depends on a subtle freedom: the ability to distort its own geometry slightly, reshaping itself to maximize stability. The hydrogen-bonded framework locked that distortion out. Stripped of its adaptive advantage, copper no longer dominated — the hierarchy inverted.
The implications reach well beyond a single metal's demotion. If stability is a product of environment rather than intrinsic atomic nature, then chemists can engineer it — designing systems that selectively favor one metal over others in a mixture, or building catalysts that mimic how proteins in living cells choose between copper, zinc, and iron. The principle bridges synthetic chemistry and biology in ways that were previously difficult to operationalize.
First author Haneul Im, a combined master's and PhD student at KAIST, received the Best Poster Award at the International Conference on Coordination Chemistry in Denmark — the only Korean student recognized that year. The paper appeared in the Journal of the American Chemical Society on September 3, 2026, supported by South Korea's Young Scientist Grants program. What began as a question about copper's place in a ranking has opened a broader possibility: that the design of selective metal systems, long constrained by assumed hierarchies, now has room to move.
For decades, copper has held a predictable place at the top of the stability ladder. Among the transition metals—iron, nickel, cobalt, and the rest—copper forms the strongest bonds with surrounding molecules. This ranking, known as the Irving-Williams series, has been treated as an immutable fact of chemistry, a consequence of how electrons arrange themselves within each metal's atomic structure. Change the metal, change the stability. That was the rule.
But in early September, a team at KAIST in South Korea published work that upended this assumption. They didn't swap out the copper for something else. They didn't redesign the molecules that grip the metal directly. Instead, they tuned the hydrogen bonds floating in the space around the metal—weak forces, peripheral players in the chemical drama—and copper tumbled from its throne.
The researchers, led by Professor Yunjung Baek, built their experiment around flavin, a compound found in vitamin B2. They created metal complexes by placing different metals—manganese, iron, cobalt, nickel, copper, zinc—into structures based on flavin derivatives, modified versions of the original molecule. The crucial constraint: every metal occupied the same basic geometric arrangement. The coordination structure, the way each metal bonded to its immediate neighbors, stayed constant. Only the hydrogen bonding in the outer shell varied.
What they discovered was that copper, for all its electronic sophistication, has a weakness. When copper bonds with surrounding molecules, it naturally wants to distort its geometry slightly, to shift and reshape itself into a configuration that maximizes its own stability—like someone adjusting their posture to find the most comfortable seat. The hydrogen-bonded framework the team constructed, however, locked copper in place. It prevented that crucial distortion. Stripped of its ability to reshape itself, copper lost the extra stabilization it normally gains. The result was an anti-Irving-Williams trend: copper no longer dominated. The hierarchy flipped.
The significance runs deeper than a single metal's fall from grace. For generations, chemists have understood metal stability as an intrinsic property, baked into each element's nature. This work demonstrates that stability is negotiable. It can be rewritten by the environment surrounding the metal. That distinction matters enormously for practical chemistry. If you can make one metal bond more strongly than others within a mixture, you can selectively extract it. If you can tune the environment to favor one metal's reactivity over another's, you can design better catalysts. The principle mirrors how proteins and enzymes in living cells choose which metal to use—how they select copper or zinc or iron from a crowded cellular environment. Now chemists have a template for building artificial systems that work the same way.
The work was presented at the International Conference on Coordination Chemistry in Denmark, where Haneul Im, the study's first author and a combined master's and PhD student at KAIST, received the Best Poster Award—the only Korean student honored that year. The full paper, titled "When Copper Falls: Overriding the Irving-Williams Stability Trend through Outer-Sphere Hydrogen Bonding," appeared in the Journal of the American Chemical Society on September 3, 2026. Six authors contributed to the research, which was funded by the Young Scientist Grants program of South Korea's Ministry of Science and ICT. The finding opens a new door: if stability can be engineered through the surrounding environment, then the design of selective metal separation systems and biomimetic catalysts—chemical machines that replicate nature's own strategies—moves from theoretical possibility into practical reach.
Citas Notables
The key point of this study is not simply that we lowered copper's stability, but that we showed the order of bonding stability, long regarded as an inherent property of each metal, can be changed through the surrounding environment.— Professor Yunjung Baek, KAIST Department of Chemistry
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