Anisotropic compressibility and structural stability of LLM-105 under high pressure

Area of Science:

• Materials Science
• Crystallography
• Physical Chemistry

Background:

• Understanding the high-pressure behavior of energetic materials like 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) is crucial for optimizing detonation performance and safety.
• The microscopic structural response of LLM-105 to external compression is not well understood.

Purpose of the Study:

• To investigate the structural stability and compressibility of LLM-105 under high pressure.
• To elucidate the microscopic mechanisms governing its response to compression.
• To understand the impact of pressure on its electronic properties.

Main Methods:

• High-pressure single-crystal X-ray diffraction.
• In situ Raman spectroscopy.

Main Results:

• LLM-105 exhibits anisotropic compressibility along the b axis up to 10.40 GPa, maintaining P21/n symmetry.
• Pressure reduces the V-shaped molecular framework folding angle and compresses intermolecular hydrogen bonds, causing amino group torsional deformation.
• Raman spectroscopy confirmed amino vibrational mode splitting around 3 GPa, indicating torsional evolution.
• The optical band gap significantly narrows by ~50% from 0.10 MPa to 28.02 GPa due to enhanced π-π orbital overlap and interlayer coupling.

Conclusions:

• The structural and electronic stability of LLM-105 under high pressure is governed by the interplay between framework folding and hydrogen bonding.
• These findings provide insights into the behavior of layered energetic crystals in extreme environments.