Multimolecular Complexes of CL-20 with Nitropyrazole Derivatives: Geometric, Electronic Structure, and Stability.

The multimolecular complexes formed between 2,4,6,8,10,12-hexanitro-2,4,6,6,8,10,12-hexaazaisowurtzitane (CL-20) and nitropyrazole compounds were investigated using B3LYP-D3/6-311G(d,p) and B97-3c methods. CL-20 in these complexes was surrounded by methyl, nitro, and amino derivatives of 4-nitropyrazole. The influence of substituents on the molecular electrostatic potential distribution of nitropyrazoles was investigated to figure out the potential electrostatic interaction sites. For the complex, the O···H hydrogen bond was popular in the intermolecular interactions, and dispersion interaction played an essential role, especially in C/CL-20 multimolecular complexes. Trigger bond analysis showed that their strength increased upon the formation of intermolecular weak interactions. Nitro group charge calculations stated that the negative charge on almost all nitro groups showed a significant increase. Therefore, the sensitivity of CL-20 seemed to be lower than the original. In addition, the transfer of electron density between CL-20 and nitropyrzoles in complexes was investigated, revealing the influence of weak interactions on the electron density of CL-20.