Chemists in Manchester and Lancaster made uranocenium, a uranium sandwich ion sought for more than 50 years, according to a Nature Communications paper and a University of Manchester release.

Uranocene holds one uranium atom between two flat rings of eight carbon atoms each. It is the uranium twin of ferrocene, the iron sandwich molecule tied to a Nobel Prize. Ferrocene forms ferrocenium when it loses an electron. Until now, no one had made the matching uranium ion, Manchester said.

Early tries in the late 1970s and early 1980s seemed to destroy the molecule. The Manchester team found the problem was a salt rich in fluorine that labs use to help current flow. The new ion strips fluorine from that salt and breaks down. By picking a different chemical to remove the electron and a gentler solvent, the team grew crystals that stayed stable at room heat, Manchester reported.

Cameron Deakin and colleagues at Manchester led the lab work. Andrew Kerridge at Lancaster University ran the computer models, the release said. X-ray maps, magnet tests and spin tests showed the uranium had lost one more electron. It moved from a +4 to a +5 state. Current tests showed uranocene and uranocenium switch as cleanly as ferrocene and ferrocenium, Manchester said.

Conrad Goodwin of Manchester said the molecule barely changes shape when it loses an electron. That is because uranium shares electrons with carbon, according to the release. Chemists now have matching uranium sandwich molecules in the +3, +4 and +5 states. They can study how the atoms bond with little shape change. The paper is titled "Isolation of uranocenium, the bis-[8]annulene uranium cation."

What we know: Researchers made stable uranocenium crystals and showed a clean switch like ferrocene.
What we don't: How the new ion will react in later tests, or whether heavier elements form the same ion.