Stacking in Layered Covalent Organic Frameworks: A Computational Approach and PXRD Reference Guide.

Area of Science:

• Materials Science
• Computational Chemistry
• Crystallography

Background:

• Layered covalent organic frameworks (LCOFs) exhibit diverse stacking arrangements that dictate their properties.
• Understanding and characterizing stacking disorder is crucial for tailoring LCOF functionality.

Purpose of the Study:

• To develop and apply an ab initio-based workflow for characterizing stacking disorder in COF-1.
• To correlate powder X-ray diffraction (PXRD) features with specific stacking configurations.
• To investigate the energetic landscape governing stacking arrangements in COF-1.

Main Methods:

• Simulated powder X-ray diffraction (PXRD) analysis.
• Quantum-mechanical potential energy surface calculations.
• Construction of disordered models using Boltzmann-weighted probabilities.

Main Results:

• Periodic high-symmetry stacking motifs were ruled out for COF-1 based on experimental PXRD data.
• A comprehensive "PXRD reference guide" was established to interpret slipped structures.
• Energy landscapes revealed multiple accessible minima, indicating inevitable stacking disorder.
• Disordered models accurately reproduced experimental PXRD patterns, confirming dominant disordered stacking.

Conclusions:

• The developed ab initio workflow effectively characterizes stacking disorder in LCOFs.
• Disordered stacking is prevalent in COF-1, yet open pore channels are maintained.
• The findings provide a framework for interpreting experimental PXRD data of slipped structures.