High-Energy-Density Materials: An Amphoteric N-Rich Bis(triazole) and Salts of Its Cationic and Anionic Species.

Emmanuele Parisi,Sabrina Wahler,Alessandro Landi,Thomas M Klapötke,Andrea Peluso,Sandra Fusco,Carla Manfredi,Roberto Centore

doi:10.1021/acs.inorgchem.1c02002

Abstract

The synthesis and characterization of the N-rich bis(triazole) compound 1H,4′H-[3,3′-bis(1,2,4-triazole)]-4′,5,5′-triamine (C4H7N9) with a N content of 69.6% by weight is reported. The compound exhibits a rich acid–base behavior because it can accept up to two protons, forming a monocation and a dication, and can lose one proton, forming an anion. Measurement of the acid constants has shown that there exist well-defined pH intervals in which each of the four species is predominant in solution, opening the way to their isolation and characterization by single-crystal X-ray analysis as salts with different counterions. Some energetic salts of the monocation or dication containing oxidizing inorganic counterions (dinitramide, perchlorate, and nitrate) were also prepared and characterized in the solid state for their sensitivity. In particular, the neutral compound shows a very remarkable thermal stability in air, with Td = 347 °C, and is insensitive to impact and friction. Salts of the dication with energetic counterions, in particular perchlorate and nitrate, show increased sensitivities and reduced thermal stability. The salt of the monocation with dinitramide as the counterion outperforms other dinitramide salts reported in the literature because of its higher thermal stability (Td = 230 °C in air) and friction insensitiveness.

Highlights

High-energy-density materials (HEDMs) can store and release in a controllable manner a high amount of energy; they are widely exploited in military and civil areas.[1]
N-rich heterocycles generally contain N in negative oxidation states, and these materials can decompose, giving environmentally benign gases. Another advantage of N-rich heterocycles is the presence of basic N atoms or acidic N−H groups, which can lead to the formation of coordination compounds or salts in which the N-rich heterocycle is present as a cation or an anion
Tautomerism is a phenomenon common to several classes of N-containing aromatic heterocycles, exhibiting many intriguing aspects that are relevant in many areas, including crystal engineering,[13] drug design,[14] energetic materials,[15] and coordination chemistry.[16,17]

Summary

Introduction

High-energy-density materials (HEDMs) can store and release in a controllable manner a high amount of (chemical) energy; they are widely exploited in military and civil areas.[1]. We note that neutral 1 and its singly and doubly protonated species (Chart 1) are characterized by the presence of several strong H-bonding donor and acceptors on the rim of the molecule. The cation is present as the 1H−1′H tautomer (Figure 4a), consistent with the results of computational analysis, so single protonation of 1 is observed at the triazole ring bearing two amino groups.

Results

Conclusion