This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In a study published in Nature Communications, researchers from The University of Manchester and Lancaster University have isolated and characterized uranocenium, the positively charged form of a landmark uranium compound called uranocene. The work shows that this long-sought molecule is stable, and that it behaves in a way that challenges how chemists usually think about bonding in heavy elements.
Uranocene is a 'sandwich' molecule: a single uranium atom held between two flat rings, each made of eight carbon atoms. It is the uranium counterpart of ferrocene, an iron sandwich molecule whose discovery contributed to the 1973 Nobel Prize in Chemistry. Ferrocene readily gives up an electron to form the ferrocenium cation, a switch so clean and reliable that it is used as a reference standard in laboratories worldwide.
Until now, no one had been able to isolate the equivalent uranium compound. When chemists first tried to remove an electron from uranocene in the late 1970s and early 1980s, the molecule appeared to fall apart, giving poorly defined products. The Manchester team found that the problem lay not with uranocene itself, but with a fluorine-containing salt routinely used in those experiments to help solutions conduct electricity better, an electrolyte.
The uranocenium cation strips fluorine from this salt and decomposes in the process. By choosing a different chemical to remove the electron and a less reactive solvent, the team isolated uranocenium as crystals stable at room temperature. The breakthrough began partly by chance: the reaction was designed for a different purpose, but uranocenium was produced instead.
The team, including Cameron Deakin, Iulia Turcas, Benjamin Réant, Liam Griffin, John Seed, Adam Brookfield, professor David Collison, professor Eric McInnes and Dr. Conrad Goodwin from Manchester, and Dr. Andrew Kerridge from Lancaster University, then studied the compounds in detail.
They used single-crystal X-ray diffraction, which maps the positions of atoms in a crystal, alongside magnetic and electron paramagnetic resonance (EPR) measurements, which probe the unpaired electrons inside a molecule, and computer modeling. Together, these confirmed that the uranium has given up one more electron than in uranocene, raising its "oxidation state" from +4 to +5. Electrochemical experiments, which measure how easily a molecule gains or loses electrons, showed that uranocene and uranocenium switch back and forth as cleanly as ferrocene and ferrocenium do.
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