Porous molecular crystals by macrocyclic coordination supramolecules

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Designing functional porous materials is crucial for applications like gas storage and separation.
• Supramolecular self-assembly offers a versatile route to construct complex architectures with tunable properties.

Purpose of the Study:

• To investigate the formation of distinct supramolecular isomers (coordination polymers and macrocycles) using silver ions, functionalized ligands, and specific counter-anions.
• To characterize the resulting cubic structures and evaluate their permanent microporosity and gas adsorption selectivity.

Main Methods:

• Synthesis of five thioether-functionalized bis(pirazolyl)methane ligands.
• Coordination of ligands with silver ions (Ag(+)) and counter-anions (triflate, CF3SO3(-), and hexafluorophosphate, PF6(-)).
• Structural characterization using X-ray diffraction and gas adsorption isotherms.
• Solid-state NMR spectroscopy to study guest molecule diffusion.

Main Results:

• Two distinct supramolecular isomers were formed: helicoidal coordination polymeric chains with CF3SO3(-) and hexameric macrocycles with PF6(-).
• Hexameric macrocycles self-assemble into cubic structures with permanent microporosity, exhibiting selective adsorption of CO2 and N2O over CH4 and N2.
• Ligand functionalization modulated the microporosity, and solid-state NMR confirmed guest accessibility to the cavities.

Conclusions:

• The judicious choice of metal ions, ligands, and counter-anions enables the rational design of complex supramolecular architectures.
• The synthesized cubic materials demonstrate potential for selective gas separation applications.
• Ligand modification provides a strategy to tune the pore size and adsorption properties of these porous coordination materials.