Reversible pressure pre-amorphization of a piezochromic metal-organic framework

Area of Science:

• Materials Science
• Chemistry
• Physics

Background:

• Piezochromic materials exhibit color changes in response to applied pressure.
• Metal-organic frameworks (MOFs) are versatile crystalline materials with tunable properties.
• Understanding pressure-induced phase transitions is crucial for materials design.

Purpose of the Study:

• To investigate the pressure-induced structural and optical changes in the piezochromic MOF Co2(Bdc)2Dabco·4DMF·H2O.
• To elucidate the mechanism of pre-amorphization and its effect on material properties.
• To correlate structural distortions with changes in optical absorption and color.

Main Methods:

• Single-crystal X-ray diffraction to monitor structural changes under pressure.
• Spectroscopic analysis to observe changes in optical absorption.
• Computational modeling to understand distortion mechanisms (implied).

Main Results:

• The MOF transitions from a tetragonal phase (α) to a pre-amorphized phase (β) starting at 0.7 GPa.
• Significant pressure-induced shortening of translational correlations occurs around 1.9 GPa.
• The material exhibits a visible color change from blue to red due to altered VIS absorption, driven by Bdc linker distortions and Co(ii) coordination changes.

Conclusions:

• The piezochromism in this MOF is a result of pressure-induced structural distortions and pre-amorphization.
• These structural changes directly influence the electronic structure and optical properties.
• The study provides insights into the pressure-responsive mechanisms of MOFs.