Crystal Structure Prediction of Bifurazano[3,4-b:3′,4′-f][3′′,4′′-d](BFFO) in the Experimentally Known Monohydrated and Proposed Anhydrous Forms

Bifurazano[3,4-b:3′,4′-f][3′′,4′′-d]xacycloheptatriene (BFFO, C6N6O5) is perspective high-energy-density compound. The crystal structure was previously determined for its monohydrate (space group P21/c, Z=4), while it remains unknown for pure BFFO being of primary interest. Herein a theoretical crystal structure prediction of BFFO in both monohydrated and the proposed anhydrous forms is performed. The Coulomb energy was calculated with advanced point charge models reproducing with high accuracy electrostatic potentials of the BFFO and water molecules. The van der Waals energy was calculated with empirical atom-atom potentials. The global search for energy minima involved enumeration of 35 most likely organic structural classes with one and two independent molecules (Z=1 and 2). A characteristic feature of the energy landscape of an anhydrous BFFO is that the energies of the deepest minima differ very little. However the structures in the space group Pbca, Z=8 and P21/c, Z=8 were found the most energetically preferable. The common feature of predicted BFFO structures is the presence of herring-bone packing motifs instead of stacking configurations. The detonation pressure and velocity of pure BFFO crystal (presumably a high-energy explosive) are estimated from the predicted density; the latter occurs to be lower than density of the monohydrate form. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim