Amphidynamic Molecular Crystal with Temperature-Controlled Helical Hydrogen-Bonded Network: Proton Dynamics and...

Area of Science:

• Materials Science
• Crystallography
• Supramolecular Chemistry

Background:

• Amphidynamic organic crystals are rare, with limited understanding of their dynamic behavior.
• Imidazolium and carboxylic acid compounds offer potential for novel crystal structures.
• Helical hydrogen bonding networks are key to unique material properties.

Purpose of the Study:

• To investigate the first observed amphidynamic organic crystal, hydrated imidazolium hemimelitate.
• To analyze the temperature-dependent behavior and phase transitions of this unique material.
• To elucidate the molecular dynamics and proton-phonon coupling mechanisms.

Main Methods:

• Terahertz (THz), Far-Infrared (FIR), Mid-Infrared (MIR), and Raman spectroscopies were used for analysis.
• Density Functional Theory (DFT) calculations were employed to model molecular dynamics.
• Temperature-dependent spectroscopic analysis was conducted across a wide spectral range.

Main Results:

• The crystal exhibits a static acid ion sublattice and a dynamic sublattice of imidazole ions and water molecules.
• A transition from positional to orientational disorder of water molecules was observed near room temperature.
• An order-disorder phase transition occurred at 150 K, with proton-phonon coupling below 100 K.

Conclusions:

• Hydrated imidazolium hemimelitate represents a novel class of amphidynamic organic crystals.
• Understanding temperature-dependent hydrogen bond behavior and coupling effects is vital for designing amphidynamic materials.
• The findings offer insights into molecular dynamics and phase transitions in complex organic crystals.