A theoretical investigation into the effect of solvent on crystal morphology of 1-methyl-3,4,5-trinitro-1H-pyrazole (MTNP)

The solvent has a significant effect on the crystal morphology of 1-methyl-3,4,5-trinitro-1H-pyrazole (MTNP). The attachment energy model was employed to predict the crystal morphology of MTNP in vacuum, and the main habit facets were obtained. On this basis, the interface models between the ethanol solvent and the crystal surface were constructed and simulated by molecular dynamics method, their interactions were analyzed in detail by radial distribution function and mean square displacement. The final crystal morphology of MTNP in ethanol solvent was obtained using the modified attachment energy model. The results show that MTNP crystals simulated in vacuum have up to 10 habit faces, of which the (1 1 0) and (2 0 0) faces are morphologically more important, accounting for 43.67% and 10.59% of the total surface area, respectively. There is significant hydrogen bonding interaction between the crystal surfaces and the ethanol solvent, which alters the relative growth rates of the different faces and leads to changes in the crystal morphology. The diffusing ability of the ethanol solvent on the crystal face also has a non-negligible effect on the interaction, and the stronger the diffusing ability, the more favorable the interaction. In the presence of ethanol solvent, the (2 0 0) surface disappears and the crystal morphology of MTNP shows a fusiform.