Theoretical studies on the structures, material properties, and IR spectra of polymorphs of 3,4-bis(1H-5-tetrazolyl)furoxan

Theoretical studies on the structures, densities, and heats of formation of conformational isomers of 3,4-bis(1H-5-tetrazolyl)furoxan (H₂BTF) were performed based on density functional theory (DFT) calculations. Two stable planar conformational isomers, the face-to-back and the back-to-face conformers, and one stable slightly twisted conformer, the back-to-back conformer, were predicted for H₂BTF at the M06-2X/6-311 + G(d,p) level of theory. The face-to-back conformer was calculated to be the most stable conformational isomer on the potential energy surface. No stable face-to-face conformer, whether planar or tilted, was identified in the calculations. The Vienna Ab Initio Simulation Package (VASP) was used in combination with molecular dynamics simulation to explore the stable crystal forms and the densities of the stable conformational isomers. Two of them exhibited high densities: the face-to-back conformer with P2₁ symmetry (2.01 g/cm³) and the back-to-back conformer with Pna2₁ symmetry (2.05 g/cm³). Their heats of formation were also predicted to be high when calculated at the same DFT level. The detonation pressures and velocities of these polymorphs, as calculated using the EXPLO5 program, are well above those of many advanced high energy density materials, pointing to the potential use of these conformers as novel explosives with good detonation performance. Also, IR spectra are shown to be able to distinguish these denser polymorphs of H₂BTF. This study suggests that it could be worth investigating whether denser polymorphs of H₂BTF can be grown.