Chemists trap americium in a silver cage

A long-standing question in actinide chemistry is how 5f orbitals participate in bonding and whether their contribution can be deliberately controlled. Although researchers have shown that external stimuli such as pressure, light, and heat can alter actinide bonding, Yaxing Wang and his colleagues at Soochow University “wondered whether chemical confinement could achieve a similar effect,” Wang says in an email.

To test that idea, the researchers confined the americium cluster inside highly charged silver nanocages known for their ability to encapsulate ions and other guest species. They found that the metallic cages fundamentally alter how the radioactive element bonds to its surroundings, revealing confinement as a new handle for manipulating actinide electronic structure (J. Am. Chem. Soc. 2026, DOI: 10.1021/jacs.6c05101).

“The challenge lies in the complex, often unpredictable nature of 5f orbital involvement in bonding,” Wang says, “which makes it difficult to control or even probe systematically.”

Confinement within the silver cage compresses and polarizes the americium unit, suppressing orbital overlap between americium 5f orbitals and oxygen atoms, which is one of the key drivers of covalency.

“The silver nanocage does not simply house the [americium] cluster passively; it actively confines it, lengthening the average Am–O bond,” says Wang. This bond elongation indicates a weakening of Am–O covalency.

By selectively dampening this contribution while leaving other bonding interactions intact, the silver cage effectively acts as a nanoscale tuning knob for actinide electronic structure.

Though the researchers have not yet carried out any practical experiments, beyond advancing fundamental understanding of actinide bonding, they envision this approach informing the design of next-generation materials for nuclear separations, waste management, f-element magnetic and electronic materials, as well as catalysis.

“Next, we aim to encapsulate a series of actinide elements, including uranium (U), neptunium (Np), plutonium (Pu), americium (Am), and curium (Cm)” and observe their behavior, Wang says.