Structure elucidation of a complex CO₂-based organic framework material by NMR crystallography.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Supramolecular Chemistry

Background:

• Complex organic frameworks are crucial for various applications.
• Determining the precise three-dimensional structure of these materials is challenging.
• Self-assembly processes often rely on intricate intermolecular interactions.

Purpose of the Study:

• To determine the de novo three-dimensional structure of a complex CO2-based organic framework.
• To elucidate the role of the hydrogen-bonding network in the material's self-assembly selectivity.
• To evaluate the utility of solid-state NMR crystallography for complex solid materials.

Main Methods:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy, including Dynamic Nuclear Polarization (DNP)-enhanced experiments.
• Two-dimensional through-space and through-bond correlation NMR experiments for resonance assignment.
• Molecular Mechanics (MM) and Quantum Mechanics (QM) calculations for structure modeling.
• Powder X-ray Diffraction (PXRD) for structural validation.

Main Results:

• A complete assignment of 15N, 13C, and 1H resonances was achieved.
• A detailed 3D structural model of the CO2-based organic framework was successfully determined.
• An optimized hydrogen-bonding network was identified as the key factor for self-assembly selectivity.
• PXRD was found to be less effective than NMR for structural modeling in this context.

Conclusions:

• Solid-state NMR crystallography is a powerful tool for determining the structure of complex organic frameworks.
• The identified hydrogen-bonding network explains the observed selectivity in the self-assembly process.
• The NMR crystallography approach is adaptable for characterizing other complex solid materials.