A ‘trophy molecule’ that has eluded scientists for decades has been created in a stable form for the first time by researchers in Nottingham.
Chemists from the University of Nottingham have prepared a terminal uranium nitride compound – containing a uranium-nitrogen triple bond – which is stable at room temperature and can be stored in jars in crystallised or powder form.
The breakthrough could have implications for the nuclear energy industry as uranium nitride material could provide a viable alternative to mixed oxide nuclear fuels since nitrides exhibit superior high densities, melting points and thermal conductivities.
Previous attempts to prepare a terminal uranium nitride have required low temperatures – 5K or -268°C – or mixing dinitrogen or ammonia with uranium under high temperature and pressure but this process introduces impurities that are difficult to remove. The new technique uses an altogether different technique.
“The beauty of this work is its simplicity – by encapsulating the uranium nitride with a very bulky support ligand, stabilising the nitride during synthesis with sodium, and then sequestering the sodium under mild conditions we were able to at long last isolate the terminal uranium nitride linkage,” said Dr Stephen Liddle from the School of Chemistry.
“A major motivation for doing this work was to help us understand the nature and extent of the covalency in the chemical bonding of uranium. This is fundamentally interesting and important because it could help in work to extract and separate the 2-3% of the highly radioactive material in nuclear waste.”
The uranium-nitride contains and unpaired electron and by using Electron Paramagnetic Resonance (EPR) spectroscopy at the University of Manchester, researchers found it behaved differently from similar compounds.
“EPR spectroscopy can give detailed information about the local environment of unpaired electrons, and this can be used to understand the electronic structure of the uranium ion in this new nitride,” said Professor Eric McInnes, from Manchester. “It turns out this new nitride behaves differently from some otherwise analogous materials, and this might have important implications in actinide chemistry which is of vital technological and environmental importance in the nuclear fuel cycle.”