Unraveling the direct effect of hydrogen bonding on density and thermostability of energetic materials through isomerism

Introduction of additional donors or acceptors for strengthening hydrogen-bonding (HB) interactions is one of the most commonly utilized methods to improve the density and thermostability of organic functional materials, including energetic materials. However, this method can lead to changes in the molecular composition, obscuring the direct effects of HB. To address this issue, we propose an effective strategy, based on isomerism, for determining the direct effects of HB interactions. We designed and synthesized two isomers, 2,4,6,8-tetranitro-1,5-diamine-naphthalene (3a) and 1,3,6,8-tetranitro-2,7-diamine-naphthalene (3b). X-ray diffraction analysis, quantum calculations, and experimental investigations revealed that 3a, which has stronger a intermolecular HB, exhibits closer molecular packing and, thus, a higher density (1.905 g cm⁻³) than 3b (1.840 g cm⁻³). By contrast, 3b, which has a stronger intramolecular HB, exhibits a higher degree of aromaticity and, thus, a higher thermostability (decomposition temperature (T_d) = 330 °C) than 3a (T_d = 256 °C). Thus, after eliminating interference from compositional changes, it is clear that stronger intermolecular HB interactions are conducive to an increase in density, whereas stronger intramolecular HB interactions are conducive to a thermostability increase. In addition, the densities and thermostabilities of 3a and 3b are high, and the preparation method is simple, involving only two steps. Both compounds are highly insensitive (IS > 40 J and FS > 360 N), and the detonation performance is comparable to that of HNS and PYX. These results strongly suggest that 3a and 3b could be applied as insensitive heat-resistant energetic materials.