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.

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.