Metal-organic polyhedral frameworks: high h(2) adsorption capacities and neutron powder diffraction studies

Area of Science:

• Materials Science
• Chemistry
• Crystallography

Background:

• Metal-organic frameworks (MOFs) are porous materials with potential applications in gas storage and separation.
• NOTT-112 is a specific MOF known for its cuboctahedral cages and paddlewheel nodes containing copper ions.
• Understanding the precise binding sites of guest molecules within MOFs is crucial for optimizing their performance.

Purpose of the Study:

• To investigate the initial binding sites of deuterium (D2) in the NOTT-112 MOF.
• To determine if D2 exhibits selectivity for different copper ion environments within the framework.
• To elucidate the structural changes upon D2 adsorption using neutron powder diffraction.

Main Methods:

• Neutron powder diffraction was employed to study D2-loaded NOTT-112.
• Analysis focused on identifying the location and coordination of D2 molecules with respect to the copper centers.
• Quantitative analysis of diffraction data was used to determine binding distances and site occupancy.

Main Results:

• Deuterium (D2) was found to bind preferentially to the axial sites of exposed Cu(II) ions located in the smallest cuboctahedral cages.
• This binding demonstrates a clear discrimination between the two types of exposed Cu(II) sites at the paddlewheel nodes.
• The determined Cu-D2 distance was 2.23(1) Å, indicating a specific interaction.

Conclusions:

• The Cu(II) centers within the cuboctahedral cage are the primary and strongest binding sites for D2 in NOTT-112.
• This selective binding highlights the potential of NOTT-112 for applications requiring selective gas adsorption, such as deuterium separation or storage.
• The findings provide valuable insights into the structure-property relationships governing gas interactions in MOFs.