Understanding the Pseudoflexibility of a Co-btc Coordination Polymer

Area of Science:

• Materials Science
• Inorganic Chemistry
• Crystallography

Background:

• Coordination polymers (CPs) are versatile materials with tunable properties.
• Understanding structural transformations in CPs is crucial for their application.
• The dynamic behavior of CPs, often termed flexibility, is an active area of research.

Purpose of the Study:

• To synthesize and characterize a new functionalized cobalt-based coordination polymer (CP 1).
• To investigate the structural transformation of CP 1 in the presence of moisture and its reversibility.
• To elucidate the mechanism behind the observed structural transformation and introduce the concept of 'pseudoflexibility' in CPs.

Main Methods:

• Single-crystal X-ray diffraction (SCXRD) for structural determination of CP 1 and CP 2.
• Chemical synthesis involving 1,3,5-trimesic acid, cobalt chloride, and N,N-dimethylacetamide.
• Mechanistic studies to understand the transformation pathway between the two CPs.

Main Results:

• A new functionalized CP, [Co2(DMA)3(btc)Cl]n (CP 1), was synthesized.
• CP 1 undergoes a reversible structural transformation to [Co3(btc)2·12H2O]n (CP 2) in moisture, and back to CP 1 with DMA.
• The transformation involves metal-carboxylate bond changes, altered coordination geometry, and ligand coordination mode shifts, revealing a degradation-recovery mechanism termed 'pseudoflexibility'.

Conclusions:

• The study demonstrates a unique reversible structural transformation in cobalt-based CPs, termed 'pseudoflexibility'.
• It highlights that CPs can be recovered even after apparent degradation by understanding the reaction mechanism.
• A novel strategy for synthesizing functionalized CPs from stable CPs was developed, opening new avenues for CP design and recovery.