First-principles study on energetic cocrystals of CL-20/4,5-MDNI with two different stoichiometric ratios under high pressure

CONTEXT

This research determined the crystal structure, molecular structure, electronic structure, optical properties, mechanical properties, and Hirshfeld analysis of the CL-20/4,5-MDNI cocrystal at two distinct stoichiometric ratios under hydrostatic pressures varying from 0 to 100 GPa. The findings revealed that the CL-20/4,5-MDNI cocrystal with a 1:1 ratio experienced two structural transitions at pressures of 80 GPa and 90 GPa. Notably, new covalent bonds, C10-O13 and C9-O14, were established, whereas the C10-H10C bond was disrupted. In contrast, the CL-20/4,5-MDNI cocrystal with a 1:3 ratio underwent three structural transformations at pressures of 55 GPa, 63 GPa, and 95 GPa, leading to the creation of new covalent bonds such as C17-N35, C25-N43, C14-O9, C21-O7, and N27-H9. These transitions were corroborated through the examination of lattice parameters, variations in covalent bond lengths, density of states, and optical coefficients. Additionally, the study explored the similarities and differences between the two cocrystals in terms of their crystal structure, molecular structure, electronic properties, optical properties, mechanical properties, and Hirshfeld analysis.

METHOD

In this investigation, the CASTEP module from the Materials Studio software package was utilized to perform first-principles calculations based on density functional theory (DFT). Specifically, the Broyden-Fletcher-Goldfarb-Shanno (BFGS) optimization technique was applied to refine the geometric structures of the CL-20/4,5-MDNI cocrystals, which were prepared in the stoichiometric ratios of 1:1 and 1:3. These calculations were conducted under a range of hydrostatic pressures, varying from 0 to 100 GPa. To achieve a fully relaxed state at atmospheric pressure, the Perdew-Zunger local density approximation (LDA/CA-PZ) functional was employed. The plane wave cutoff energy was meticulously set at 489 eV to ensure the convergence of the total energy within the unit cell system. Additionally, the k-point mesh was configured as 1 × 1 × 1 to facilitate accurate calculations. Before each simulation, different hydrostatic pressures were systematically applied to analyze the structural changes under varying conditions.

Theoretical study on the correlation between the structure, excess energy, surface energy, electronic structure, nitro charge, and friction sensitivity of N,N'-dinitroethylenediamine (EDNA)

The sensitivity of energetic materials along different crystal directions is not the same and is anisotropic. In order to explore the difference in friction sensitivity of different surfaces, we calculated the structure, excess energy, surface energy, electronic structure, and the nitro group along (1 1 1), (1 1 0), (1 0 1), (0 1 1), (0 0 1), (0 1 0), and (1 0 0) surfaces of EDNA based on density functional theory. The analysis results showed that relative to other surfaces, the (0 0 1) surface has the shortest N-N average bond length, largest N-N average bond population, smallest excess energy and surface energy, widest band gap, and the largest nitro group charge value, which indicates that the (0 0 1) surface has the lowest friction sensitivity compared to other surfaces. Furthermore, the conclusions obtained by analyzing the excess energy are consistent with the results of the N-N bond length and bond population, band gap, and nitro charge. Therefore, we conclude that the friction sensitivity of different surfaces of EDNA can be evaluated using excess energy.

Investigation of Ethylenedinitramine as a Versatile Building Block in Energetic Salts, Cocrystals, and Coordination Compounds

Ethylenedinitramine (H₂EDN, 1) was prepared in a simple manner and with a high overall yield by direct nitration of 2-imidazolidinone using 100% HNO₃ at 0 °C and subsequent hydrolysis in water at 100 °C. The versatility of 1 allows its application as starting material for a broad range of different materials. It was used for the preparation of both various salts and cocrystalline materials incorporating varying amounts of the TATOT moiety. Furthermore, H₂EDN was successfully applied in the concept of energetic coordination compounds (ECCs) resulting in five copper(II) and two silver(I) complexes. A reaction path for the direct precipitation or slow crystallization of 17 different salts, including several alkali, alkaline earth, silver, and nitrogen-rich samples, is presented. The substances were extensively characterized by low-temperature single-crystal X-ray diffraction, elemental analysis (EA), IR spectroscopy, differential thermal analysis (DTA), and thermogravimetric analysis (TGA), proving their high thermal stability, especially of the alkali salts. In addition, 1 and all salts were characterized by ¹H, ¹³C, and ¹⁴N NMR, whereas 1 was also investigated using the beneficial ¹H-¹⁵N HMBC NMR spectroscopy. The sensitivities toward various mechanical stimuli according to BAM standard methods, as well as ball drop impact and electrostatic discharge (ESD) were determined using the BAM 1-out-6 method. Hot plate and hot needle tests were performed, followed by further characterization of the copper(II)-based ECCs through laser ignition experiments and UV-vis spectroscopy, offering new candidates for nontoxic, less sensitive laser-ignitable materials. Several detonation parameters were calculated using EXPLO5 (V6.05.02).

Interpol review of detection and characterization of explosives and explosives residues 2016-2019

This review paper covers the forensic-relevant literature for the analysis and detection of explosives and explosives residues from 2016-2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/Resources/Documents#Publications.

Theoretical studies on the structure and properties of DAT/BTNAT cocrystal under high pressure

The structural, electronic, and absorption properties of 3,5-diamino-1H-1,2,4-triazole (DAT) and 5,5′-bis(trinitromethyl)-3,3′-azo-1H-1,2,4-triazole (BTNAT) cocrystal under hydrostatic compression of 0–100 GPa were investigated by using periodic density functional theory with dispersion correction (DFT-D). The results indicate that a structural transformation occurred at 25 GPa. The structural transformation makes the positions of the molecules rearrange in the cocrystal and improves the stability and planarity. An analysis of the band gap and density of states indicates that the DAT/BTNAT cocrystal becomes more sensitive under compression. The absorption spectra illustrate that the DAT/BTNAT cocrystal has relatively high optical activity with the increasing pressure. Our work may offer some valuable information for understanding the behavior of energetic cocrystals under high pressure.