Pressure-Stabilized High-Energy-Density Material YN10

Polynitrogen compounds have been intensively studied for potential applications as high energy density materials, especially in energy and military fields. Here, using the swarm intelligence algorithm in combination with first-principles calculations, we systematically explored the variable stoichiometries of yttrium–nitrogen compounds on the nitrogen-rich regime at high pressure, where a new stable phase of YN10 adopting I4/m symmetry was discovered at the pressure of 35 GPa and showed metallic character from the analysis of electronic properties. In YN10, all the nitrogen atoms were sp2-hybridized in the form of N5 ring. Furthermore, the gravimetric and volumetric energy densities were estimated to be 3.05 kJ/g and 9.27 kJ/cm-1 respectively. Particularly, the calculated detonation velocity and pressure of YN10 (12.0 km/s, 82.7 GPa) was higher than that of TNT (6.9 km/s, 19.0 GPa) and HMX (9.1 km/s, 39.3 GPa), making it a potential candidate as a high-energy-density material.

Transformation of Ammonium Azide at High Pressure and Temperature

The compression of ammonium azide (AA) has been considered to be a promising route for producing high energy-density polynitrogen compounds. So far though, there is no experimental evidence that pure AA can be transformed into polynitrogen materials under high pressure at room temperature. We report here on high pressure (P) and temperature (T) experiments on AA embedded in N2 and on pure AA in the range 0–30 GPa, 300–700 K. The decomposition of AA into N2 and NH3 was observed in liquid N2 around 15 GPa–700 K. For pressures above 20 GPa, our results show that AA in N2 transforms into a new crystalline compound and solid ammonia when heated above 620 K. This compound is stable at room temperature and on decompression down to at least 7.0 GPa. Pure AA also transforms into a new compound at similar P–T conditions, but the product is different. The newly observed phases are studied by Raman spectroscopy and X-ray diffraction and compared to nitrogen and hydronitrogen compounds that have been predicted in the literature. While there is no exact match with any of them, similar vibrational features are found between the product that was obtained in AA + N2 with a polymeric compound of N9H formula.

Synthesis of magnesium-nitrogen salts of polynitrogen anions

The synthesis of polynitrogen compounds is of fundamental importance due to their potential as environmentally-friendly high energy density materials. Attesting to the intrinsic difficulties related to their formation, only three polynitrogen ions, bulk stabilized as salts, are known. Here, magnesium and molecular nitrogen are compressed to about 50 GPa and laser-heated, producing two chemically simple salts of polynitrogen anions, MgN4 and Mg2N4. Single-crystal X-ray diffraction reveals infinite anionic polythiazyl-like 1D N-N chains in the crystal structure of MgN4 and cis-tetranitrogen N44− units in the two isosymmetric polymorphs of Mg2N4. The cis-tetranitrogen units are found to be recoverable at atmospheric pressure. Our results respond to the quest for polynitrogen entities stable at ambient conditions, reveal the potential of employing high pressures in their synthesis and enrich the nitrogen chemistry through the discovery of other nitrogen species, which provides further possibilities to design improved polynitrogen arrangements.

The Reaction of Cyanamidium Salts with Ylidenecyanamide Derivatives

Cyanamidium salts 1undergo ene reactions with ylidenecyanamide derivatives 5to afford conjugated iminium salts 12. The N,N,Nʹ-trialkylcyanamidium salts 1react as the ene, and the ylidenecyanamide derivatives 5react as the enophile components to form the 2-azoniaallene salts 11 followed by the formation of conjugated iminium salts 12 as cationic polynitrogen compounds with guanidine and amidine subgroups. The constitution of the new conjugated iminium salts 12 was secured by elemental analyses and spectroscopic data (IR and NMR).

Characterizations of Novel Binuclear Transition Metal Polynitrogen Compounds: M2(N5)4 (M=Co, Rh and Ir)

Theoretical studies on a series of binuclear transition metal pentazolides M2(N5)4(M=Co, Rh and Ir) predict Paddlewheel-type structures with very short metal-metal distances suggesting high-order metal-metal multiple bonds. Natural Bonding Orbital (NBO) analysis have indicated that the bonding between the metal atom and the five-membered ring is predominantly ionic for each M2(N5)4species, and a high-order metal-metal multiple bonding exists between the two metal atoms, in addition, the presence of the delocalized π orbital plays an important role in the stabilization of this metal-polynitrogen species. Nucleus independent chemical shift (NICS) values confirm that the planar N5exhibits aromaticity in these M2(N5)4species. The values of NICS(0.0), NICS(0.5) and NICS(1.0) for Co2(N5)4are larger than those of the other two M2(N5)4species (M=Rh and Ir), with the order of Co2(N5)4>Rh2(N5)4>Ir2(N5)4. The dissociation energies into Mononuclear Fragments for M2(N5)4(M=Co, Rh and Ir) are predicted to be 82.9 (85.7), 139.9 (113.2), and 155.1 (149.7) kcal/mol, respectively. However, the dissociation energies for the loss of one pentazolato group from the M2(N5)4analysis have indicated that the Co2(N5)4is relatively higher at ~40 kcal/mol. Thermochemistry suggests Co2(N5)4to be a viable species.