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Inorganic Chemistry

Naked pentazolate caught as a silver salt

Polynitrogen compound prepared without any stabilizing species

by Bethany Halford
April 16, 2018 | A version of this story appeared in Volume 96, Issue 16


Repeating units of a complex of pentazolate, silver, and ammonia as observed in an X-ray crystal structure.
Credit: Nat. Commun.
The unit cell of the X-ray crystal structure of [Ag(NH3)2]+[Ag3(N5)4]

The pentazolate anion—a five-membered ring composed only of nitrogen atoms—has great potential as a high-energy-density material for explosive or propulsive applications. But chemists have had to stabilize the anion with molecules or ions, such as water or ammonium, that decrease the material’s overall energy density. Now, chemists led by Nanjing University of Science & Technology’s Bingcheng Hu, in collaboration with the University of Southern California’s Karl O. Christe, have prepared a silver pentazolate complex that’s devoid of stabilizing molecules or ions (Nat. Commun. 2018, DOI: 10.1038/s41467-018-03678-y). The chemists prepared the naked pentazolate complex by treating a water-stabilized magnesium pentazolate salt with silver nitrate. The resulting AgN5 is stable up to 90 °C and very sensitive to impact and friction, breaking down into only Ag and N2. However, the chemists were not able get a crystal structure of this heat- and light-sensitive, insoluble compound as a pure complex because it began decomposing to AgN3 almost immediately after it was synthesized. So, to further characterize what they’d made, the chemists treated the AgN5 with aqueous ammonia, which produced [Ag(NH3)2]+[Ag3(N5)4]. This complex was thermally stable up to 90 °C and was only moderately sensitive to impact and friction.


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