On the structural stability of ionic liquid-IRMOF composites: a computational study

Area of Science:

• Materials Science
• Computational Chemistry
• Chemical Engineering

Background:

• Isoreticular metal-organic frameworks (IRMOFs) are porous materials with tunable structures.
• Ionic liquids (ILs) are salts that are liquid at low temperatures, offering unique solvent properties.
• Confining ILs within MOF cavities is explored for potential applications in catalysis and separation.

Purpose of the Study:

• To investigate the structural stability of IRMOF-1 and IRMOF-10 when confining various ionic liquids.
• To understand the role of interactions between IL anions and MOF metal centers in structural integrity.
• To determine how IL loading affects the stability of these metal-organic frameworks.

Main Methods:

• Molecular dynamics (MD) simulations were employed to study the behavior of IRMOFs with confined ILs.
• Density functional theory (DFT) and ab initio molecular dynamics (AIMD) were used for further theoretical validation.
• A range of imidazolium- and pyridinium-based ILs with different anions (e.g., PF6-, Br-, Tf2N-, DCA-) were simulated at various concentrations.

Main Results:

• Both IRMOF-1 and IRMOF-10 exhibited significant structural instability and deformation in the presence of ILs.
• The interactions between IL anions and the metallic nodes of the IRMOFs were identified as the primary cause of structural disruption.
• Elongated anions (Tf2N-, DCA-) showed a greater tendency to destabilize the MOFs compared to spherical anions (Br-, PF6-).

Conclusions:

• The structural integrity of IRMOFs is compromised upon confinement of ionic liquids.
• The nature of the IL anion significantly influences the extent of MOF structural collapse.
• These findings highlight the importance of considering host-guest interactions for designing stable MOF-IL systems.