Reversible and selective solvent adsorption in layered metal-organic frameworks by coordination control

Area of Science:

• Materials Science
• Coordination Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are extensively studied for adsorption and separation applications due to their functionalities and thermal stability.
• Synthesizing novel MOFs with enhanced chemical stability and desired structures is a key research focus.
• Organic ligands with azolate moieties are valuable building blocks for constructing MOFs.

Purpose of the Study:

• To synthesize new 2D layered MOF structures with distinct topologies using benzo-bis(imidazole) (H2BBI).
• To investigate the structural properties and stability of the synthesized MOFs in various solvents.
• To explore the adsorption capabilities of a solvent-free MOF for selective guest molecule uptake.

Main Methods:

• Synthesis of two new 2D layered MOFs using benzo-bis(imidazole) (H2BBI) and metal salts (Zn(II) and Cd(II)).
• Structural characterization of the MOFs using techniques such as X-ray diffraction.
• Investigation of MOF stability in organic solvents and water.
• Analysis of guest molecule adsorption properties using high-resolution powder X-ray diffraction.

Main Results:

• Two new 2D layered MOFs, Framework 1 {[Zn2Cl2(BBI)(MSM)2]n} and Framework 2 {[Cd2Cl2(BBI)(DMSO)2]n}, with distinct topologies were successfully synthesized.
• Framework 1 demonstrated structural stability in various organic solvents and water.
• Framework 2 could be converted to a solvent-free MOF (3 {[Cd2Cl2(BBI)]n}) capable of reversible and selective dimethyl sulfoxide (DMSO) adsorption.
• The selective adsorption in MOF 3 is attributed to the bistable four- and five-coordinated geometry exchange of Cd(II).

Conclusions:

• The study successfully synthesized novel 2D layered MOFs with unique structural features.
• The synthesized MOFs exhibit varying stability in different media.
• A solvent-free MOF was developed with promising selective adsorption capabilities for DMSO, driven by metal center flexibility.