Structure of 1,1,5,5-tetranitro-[4]peristylane. Structure solution from molecular packing analysis

Area of Science:

• Crystallography
• Materials Science
• Computational Chemistry

Background:

• The title compound, decahydro-2,2,5,5-tetranitro-1,6:3,4-dimethanocyclobuta[1,2:3,4]dicyclopentene (C12H12N4O8), is an energetic material whose crystal structure requires detailed investigation.
• Understanding the molecular packing and crystal structure is crucial for predicting and optimizing the properties of energetic compounds.

Purpose of the Study:

• To determine the precise crystal structure of decahydro-2,2,5,5-tetranitro-1,6:3,4-dimethanocyclobuta[1,2:3,4]dicyclopentene.
• To validate computational methods for predicting crystal structures of complex organic molecules.

Main Methods:

• Utilized the MOLPAK program for molecular packing prediction, starting with an AM1-optimized molecular model.
• Performed lattice energy refinement on the predicted structures using the WMIN program.
• Conducted structure-factor calculations using X-ray diffraction data (197 Fo) up to sin theta/lambda = 0.324 A-1.

Main Results:

• The MOLPAK and WMIN procedures yielded 20 potential crystal structures, with the top candidate refined further.
• Initial structure-factor calculation resulted in an R value of 0.29.
• Final refinement yielded a low R value of 0.057 and wR of 0.067 for 730 reflections (I > 3 sigma (I)).

Conclusions:

• The crystal structure of decahydro-2,2,5,5-tetranitro-1,6:3,4-dimethanocyclobuta[1,2:3,4]dicyclopentene was successfully solved.
• The crystal packing was determined to be normal, with no unusual intermolecular distances observed.
• The study validates the combined use of MOLPAK and WMIN for predicting and refining crystal structures of energetic compounds.