US scientists have synthesised complexes that could provide us with a new insight into the chemistry of uranium, with far reaching consequences for the nuclear industry and beyond.     

Trevor Hayton and colleagues at the University of California, Santa Barbara, have made and isolated new uranium compounds containing an azide group, including uranium(V) azides. It is the first time, says Hayton, that uranium(V) azides have in fact been made. The team now hopes to harness the azide group's well-known reactivity to synthesise uranium nitride complexes.     

Uranium nitride is a ceramic compound used as a nuclear fuel. NASA is interested in using it as a future fuel for nuclear reactors used in space exploration. The compounds have also received attention recently as potential fuels for the next-generation of nuclear power systems. Actinide nitrides are particularly promising as advanced nuclear fuels since they exhibit higher thermal conductivity and higher metal density compared with the oxides that are currently used.    

Nitrides are a relatively rare functional group for uranium, says Hayton, and so few examples are available for scientists to study. He hopes, by using his new uranium azides, to carry out small-scale synthesis of uranium nitride and improve the understanding of its chemical properties. This would help scientists to predict its behaviour in nuclear waste and in the environment resulting in breakthroughs in waste processing and environmental remediation.     

Uranium is also of great fundamental interest as it possesses chemical traits that are not found in any other element, says Hayton. These unique features may result in the development of novel catalytic reactivity. Many challenges remain in uranium chemistry and in actinide chemistry in general, adds Hayton, describing it as being 'the last frontier of the periodic table'.   

Christopher Cummins, from the Massachusetts Institute of Technology, Cambridge, US, welcomes the work and says 'it elegantly unfurls a larger uranium(IV/V) coordination chemistry of azide as a nitrogen-rich pseudo-halide.'    

Sarah Corcoran   

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