Taming Hazardous Reactive Materials

for Single Crystal X-ray Diffraction Studies:

Dealing with Handling and Disorder Nightmares

Ashwani Vij

Space and Missile Propulsion Division,

AFRL/PRSP, Edwards Air Force Base, CA 93524 (U.S.A.)

Obtaining structural information for energetic molecules is a highly challenging task. These materials are often extremely reactive and involve hazardous handling techniques, in absence of organic solvents. The crystallization process utilizes highly acidic media such as anhydrous hydrofluoric acid (HF), or “inert” solvents like liquid sulfur dioxide (SO₂) and chlorosulfuryl fluoride (SO₂ClF), that are handled using stainless steel vacuum line techniques and fluorocarbon polymer reaction vessels. In case of thermally unstable compounds, low-temperature mounting techniques ensure minimal thermal decomposition. Crystal structures of some highly oxidizing nitrogen containing cations and anions will be discussed. The structures of these materials can also show disorder and twinning, which results in deviation of geometrical parameters from that calculated using a high level of theoretical calculations. The synergy between theory and experimentation will be highlighted using N₅⁺Sb₂F₁₁^- as an example. The N₅⁺ cation, synthesized in bulk in our laboratory, is the third all-nitrogen containing species that exists besides atmospheric nitrogen (N₂) and the azide (N₃^-) ion.

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