Vacuum-Induced Guest N,N'-Diethylformamide Binding in a Metastable Cd₅-Based Metal-Organic Framework

Area of Science:

• Materials Chemistry
• Crystallography
• Supramolecular Chemistry

Background:

• Metal-organic frameworks (MOFs) are porous materials with tunable structures.
• The activation process of MOFs, involving solvent removal, can significantly impact their properties.
• Understanding solvent-framework interactions is crucial for designing stable and functional MOFs.

Purpose of the Study:

• To synthesize and characterize a novel 3D metal-organic framework (MOF) with a metastable host framework.
• To investigate the structural changes occurring in the MOF upon activation (solvent removal).
• To elucidate the role of coordinated solvent molecules (N,N'-diethylformamide) during MOF activation.

Main Methods:

• Single-crystal X-ray diffraction to monitor structural changes.
• Controlled vacuum application at elevated temperatures to induce solvent release.
• Characterization of the MOF's framework and guest molecules.

Main Results:

• A new 3D MOF, [Et2NH2]2[Cd5(BTB)4(DEF)2]·4.75DEF, was successfully synthesized.
• Gentle vacuum treatment induced release of N,N'-diethylformamide (DEF) solvates, leading to pore-shape changes and Cd2+ coordination distortion.
• Further vacuum exposure caused DEF migration, symmetry breaking, and significant framework distortion, altering the MOF's topology.

Conclusions:

• The prepared MOF exhibits an intrinsically metastable framework susceptible to structural changes upon solvent removal.
• Coordinative solvent molecules like DEF play a dynamic, non-spectator role during MOF activation, influencing framework stability and topology.
• The observed structural transformations highlight the complexity of MOF activation processes and the importance of solvent management.