Impact sensitivity of aryl diazonium chlorides: Limitations of molecular and solid-state approach

Radical pair formation due to compression-induced electron transfer in crystals of energetic salts

An interesting effect was observed when studying explosive and non-explosive crystalline ionic materials at high pressures. A wide benchmark set of 76 crystals of different families was studied using the state-of-the-art methods at ambient pressure and in extremes (at 20, 50 and 100 GPa). It was found that hydrostatic compression leads to an electron transfer from the anion to the cation, which was carried out with different efficiencies for explosive and non-explosive salts. The measure of this electron transfer is reflected in the Hirshfeld charges (q) on cations, which decreased with the rise of pressure. Non-explosive materials are generally resistant to this effect, while explosives are much more susceptible. Thus, at 100 GPa, all the studied energetic salts demonstrate qcat < +0.1e, while for the non-explosive salts qcat > +0.1e. This value can be considered as a conditional boundary between explosive and non-explosive salts. The observed effect is in accord with the Szigeti's dielectric theory as well as with the electrophilicity/electronegativity equalization principle. In the present paper, we develop a mechanism of the explosive decomposition based on the assumption about formation of a radical pair as a result of the following reaction: . The study of such radicals revealed their intrinsic instability, which generally reflects either in a dissociative structure or in the presence of strongly weakened trigger bonds.

Bipentazole (N10): A Low-Energy Molecular Nitrogen Allotrope with High Intrinsic Stability

In this Letter, we report a crystal structure prediction and characterization of a molecular nitrogen allotrope N₁₀ (bipentazole) using state-of-the-art computational methods. To date, in the form of a P2₁ space group crystal, this allotrope is the most stable predicted form of nitrogen, other than N₂, in the pressure range 0-42 GPa. Its metastability at ambient conditions was justified using phonon dispersion and mechanical properties calculations as well as ab initio molecular dynamics simulations. Due to a high intrinsic stability caused by aromaticity, bipentazole may appear to be the first nitrogen allotrope stable enough for a large-scale synthesis at ambient conditions. The calculations of propulsive characteristics revealed that bipentazole is an excellent "green" energetic material. A potential strategy for the synthesis of this compound is offered and rationalized. The unique electronic structure of bipentazole makes it a strongly electrophilic all-nitrogen reagent, which can exhibit unusual chemistry.