A Pathway to the Athermal Impact Initiation of Energetic Azides

Energetic materials (explosives, propellants and pyrotechnics) are used in a broad range of public and private sector applications. The design of novel, safe materials is therefore of critical importance. Until now, no physical mechanism has been described to rationalize the impact sensitivity properties of energetic materials. Investigation therefore has required lengthy synthesis and experimental testing. Based on knowledge of the effects of mechanical impact, an ab initio model is developed to rationalize and describe the impact sensitivity of a series of crystalline energetic azide materials. It is found that electronic excitation of the azido anion is sufficient for initiation of these materials. The athermal excitation can be achieved through consideration of non-adiabatic, vibronic processes. Across the series of azides studied here, the electronic structure of the azido anion is found to remain largely constant. By considering only the relative rates of vibrational energy transfer within the crystalline materials, it is found that a direct correlation exists between the relative impact sensitivity and the rate of energy up-conversion. Thus, the present contribution demonstrates a fully ab initio method to describe the athermal initiation of ideal, crystalline energetic materials, and predict their relative sensitivity. Without the need for any experimental input beyond a crystal structure, this method therefore offers a means to selectively design novel materials for targeted application

Co-crystallisation at high pressure - an additional tool for the preparation and study of co-crystals

Crystallisation of paracetamol and piperazine from ethanol at a pressure of 0.57 GPa produced an ethanol solvate of a 2:1 co-crystal of paracetamol:piperazine. This contrasts with crystallisation from ethanol at ambient pressure for which only an unsolvated 2:1 co-crystal of paracetamol:piperazine has been obtained. The hydrogen bonding arrangements of the two compounds are very different and a striking feature of the solvate is the presence of an unusually short hydrogen bond between the phenolic and amine groups

A Harmonic Potential Function for Lithium Sodium DiFlouride

A harmonic force field for the mixed alkali halide dimer LiNaF2 is reported based on microwave centrifugal distortion coefficients and matrix-isolation vibrational frequencies for both 6LiNaF2 and 7LiNaF2, and an ab initio force field. It is compared to RHF and MP2 ab initio calculations, with a particular emphasis on determining reliable general alkali halide mean amplitudes of vibration l. Detailed comparisons between ionic model, RHF, MP2, and CCSD ab initio dipole moment values and the experimental value of 2.64(2) D are also made

Synthesis and characterization of the mixed-ligand coordination polymer Cu3Cl(N4C-NO2)2

Reduction of copper(II) chloride using sodium ascorbate in the presence of pure sodium 5-nitro-tetrazolate (NaNT) forms copper(I) 5-nitrotetrazolate – a known initiatory explosive (DBX-1) – and the novel mixed-ligand copper(I) chloride 5-nitrotetrazolate coordination polymer Cu3Cl(N4C-NO2)2, as well as mixtures of both. The reaction is controlled by the presence of seed crystals and transition metal compounds other than CuCl2. Cu3Cl(N4C-NO2)2 is obtained as a wine-red, air stable, water-insoluble, crystalline and highly sensitive explosive material with a greater crystal density, lower thermal stability and a higher sensitivity toward hydrolysis and shock than DBX-1. Efforts to obtain the stable and pure starting material are improved by crystallisation of NaNT as a tetrahydrate. Cu3Cl(N4C-NO2)2 and Na(H2O)4(NT) were characterised by single crystal and powder XRD, IR spectroscopy, magnetic and thermal measaurements, elemental analysis, particle size measurements, mass spectrometry, and by drop weight testing

Tuning energetic properties through co-crystallisation – a high-pressure experimental and computational study of nitrotriazolone : 4,4’-bipyridine.

We report the preparation of a co-crystal formed between the energetic molecule 3-nitro-1,2,4-triazol-5-one (NTO) and 4,4′-bipyridine (BIPY), that has been structurally characterised by high-pressure single crystal and neutron powder diffraction data up to 5.93 GPa. No phase transitions or proton transfer were observed up to this pressure. At higher pressures the crystal quality degraded and the X-ray diffraction patterns showed severe twinning, with the appearance of multiple crystalline domains. Computational modelling indicates that the colour changes observed on application of pressure can be attributed to compression of the unit cell that cause heightened band dispersion and band gap narrowing that coincides with a shortening of the BIPY π⋯π stacking distance. Modelling also suggests that the application of pressure induces proton migration along an N–H⋯N intermolecular hydrogen bond. Impact-sensitivity measurements show that the co-crystal is less sensitive to initiation than NTO, whereas computational modelling suggests that the impact sensitivities of NTO and the co-crystal are broadly similar