Flexible sorption and transformation behavior in a microporous metal-organic framework

Area of Science:

• Materials Science
• Crystallography
• Chemistry

Background:

• Metal-organic frameworks (MOFs) are crystalline porous materials with diverse applications.
• Understanding the structural stability and guest interactions of MOFs is crucial for their practical use.
• The specific MOF material Ni(2)(4,4 '-bipyridine)(3)(NO(3))(4) (A) was investigated for its properties.

Purpose of the Study:

• To synthesize and characterize the metal-organic framework Ni(2)(4,4 '-bipyridine)(3)(NO(3))(4) (A).
• To investigate the structural stability of the MOF after desolvation and its thermal properties.
• To explore the sorption capabilities of the MOF, particularly its interaction with toluene.
• To study the guest-driven solid-state transformation of a related MOF (B) to MOF (A).

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• Powder X-ray diffraction for bulk purity and temperature stability analysis.
• Sorption experiments to assess guest molecule uptake.
• Monte Carlo docking calculations to predict guest accommodation.

Main Results:

• The ladder structure of Ni(2)(4,4 '-bipyridine)(3)(NO(3))(4) (A) remains intact after desolvation and is stable up to 215°C.
• Despite small pore windows (12.3 Ų), the MOF admits toluene (26.6 Ų cross-sectional area) without structural changes.
• Monte Carlo simulations confirm toluene accommodation within the MOF pores.
• Exposure of Ni(2)(4,4 '-bipyridine)(3)(NO(3))(4).2C(2)H(5)OH (B) to methanol vapor induces a rapid, guest-driven transformation to crystalline MOF (A).

Conclusions:

• The synthesized MOF (A) is a thermally stable, porous material capable of accommodating larger guest molecules.
• A guest-driven solid-state transformation between related MOF structures (B to A) is demonstrated, highlighting the dynamic nature of these materials.
• Proposed mechanisms for the transformation involve the breaking of framework covalent bonds.