Exploring the effects of solvents on an organic explosive: Insights from the electron structure, electrostatic potential, and conformational transformations of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane

In order to attain comprehensive insights into the crystallization of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) from solutions, the geometric and electronic structures and conformational transformations of its β-, γ-, ε-, ζ- and η- forms in six organic solvents (ethanol, ethyl acetate, methanol, acetone, acetonitrile, and 2-propanol) were evaluated using quantum chemistry calculations. Results showed that solvents have little effect on the geometric structures of molecules but greatly impact the energy and electronic structure of CL-20. The electron density, atomic charges, and electrostatic potential of CL-20 exhibit polarization due to the solvent effect, especially in alcohols. The polarity of CL-20 increased because of the change in electron density. The transformations of the five conformers of CL-20 were studied thoroughly, and the energy barriers were evaluated using the Gibbs energies. Importantly, the reason η-CL-20 is only found in CL-20-based cocrystals was suggested. These results indicate that solvents play a critical role in crystal growth.