Researchers have succeeded in creating a crystal containing a rare bond between uranium and carbon.
In a molecule, atoms remain attached to one another thanks to their electrons. Depending on how they interact, they can form single, double, or triple bonds. They are not all identical, especially when a metal is involved.
Distribution of the 92 electrons in a uranium atom across its different electron shells.
Credit: Pumbaa, based on Greg Robson / Wikimedia Commons — CC BY-SA 2.0 UK.
Image Wikimedia
Chemists have long known how to create certain triple bonds between carbon and metals. But with uranium, a heavy metal, they had much more difficulty obtaining a particular type of bond called a “Fischer carbene”. Other uranium–carbon bonds were already known, but this precise form resisted attempts to create it.
An international team eventually found a solution. The researchers reacted a substance containing uranium with another capable of providing carbon. They obtained a red powder, followed by small crystals. The molecules they created contain two uranium atoms linked by a group comprising carbon and nitrogen.
These crystals made it possible to examine the compound’s structure using X-rays. The researchers were thus able to measure the position of the atoms and the very short distance between uranium and carbon. But this was not enough to determine the exact nature of their bond.
They therefore studied the distribution of electrons using additional measurements and computer calculations. The result confirms an interaction with the characteristics of a triple bond.
Why did this discovery require so much work? Uranium–carbon triple bonds had already been observed in very particular situations, for example at extremely low temperatures. Here, the researchers were able to isolate a solid compound and study it using standard laboratory methods.
The discovery primarily provides a better understanding of how uranium bonds with other elements. This is important for studying the heavy metals in its family, whose electrons sometimes behave differently from those of more common metals.
The researchers will now examine the possible reactions of this compound and attempt to create other molecules of the same kind. They now have a new concrete example for understanding chemical bonds that, until now, had been particularly difficult to study.