In-plane mechanical properties of terephthalate-based two-dimensional metal-organic frameworks.

Area of Science:

• Materials Science
• Nanotechnology
• Mechanical Engineering

Background:

• Two-dimensional (2D) metal-organic frameworks (MOFs) are increasingly used in applications requiring mechanical stability.
• The in-plane elastic modulus (E‖) is a critical property for understanding and predicting the mechanical behavior of 2D MOFs.
• Accurate measurement of E‖ in 2D MOFs is challenging due to their thinness and sensitivity.

Purpose of the Study:

• To measure the in-plane elastic modulus (E‖) of 1,4-benzenedicarboxylate (BDC)-based 2D MOFs.
• To investigate the relationship between the structure and mechanical properties of these 2D MOFs.
• To compare the mechanical properties of 2D MOFs with their 3D analogs and other 2D materials.

Main Methods:

• Atomic force microscopy (AFM) was used to stretch suspended thin membranes of 2D MOFs.
• In-plane elastic modulus (E‖) was determined from the stress-strain response.
• Density versus E‖ Ashby plots were used for material comparison.

Main Results:

• The 2D Zn₃(BDC)₃ MOF exhibited an E‖ of 11.2 ± 2.5 GPa, significantly lower than its 3D counterpart (25.9 ± 6.3 GPa).
• A 2D Mn analog, Mn₃(BDC)₃, showed enhanced stiffness with an E‖ of 25.5 ± 4.9 GPa.
• Comparative analysis using Ashby plots provided insights into the mechanical performance of 2D MOFs relative to other materials.

Conclusions:

• The in-plane elastic modulus of 2D MOFs is highly dependent on their specific structure and coordination.
• Reduced stiffness in 2D Zn-MOFs is attributed to the absence of interlayer covalent bonding.
• Strengthened coordination at nodes likely enhances the stiffness of 2D Mn-MOFs.
• This research provides critical data for the mechanical characterization and engineering of 2D MOFs.