Kinetic products in coordination networks: ab initio X-ray powder diffraction analysis

Area of Science:

• Materials Science
• Crystallography
• Chemical Synthesis

Background:

• Porous coordination networks (PCNs) are vital for catalysis, gas adsorption, and drug delivery, but their synthesis often yields microcrystalline products unsuitable for single-crystal X-ray analysis.
• Understanding kinetic control during PCN self-assembly is crucial for developing new materials, yet structural studies of kinetic products are limited.
• Traditional X-ray powder diffraction (XRPD) is used for phase purity but not typically for structure elucidation of complex materials.

Purpose of the Study:

• To explore the potential of kinetic control in synthesizing novel coordination networks.
• To demonstrate the application of ab initio XRPD for characterizing microcrystalline PCNs.
• To provide mechanistic insights into structural transformations and guest exchange reactions in PCNs.

Main Methods:

• Selective instant synthesis to achieve kinetically controlled porous coordination networks.
• Ab initio X-ray powder diffraction (XRPD) for three-dimensional structure determination of microcrystalline solids.
• Thermal annealing (573-723 K) and guest exchange experiments to study structural transformations.

Main Results:

• Instant synthesis selectively produced metastable PCNs not achievable via conventional methods.
• Ab initio XRPD successfully determined the crystal structures of microcrystalline kinetic products.
• Mechanistic insights into thermally induced transformations and guest inclusion/exchange reactions were gained.
• A memory effect was observed, transferring structural information from kinetic precursors to stable structures via amorphous phases.

Conclusions:

• Kinetic control and ab initio XRPD are powerful tools for synthesizing and characterizing novel porous coordination networks.
• This approach overcomes limitations of single-crystal X-ray diffraction for microcrystalline materials.
• Future applications include studying in situ reactions within PCNs and understanding complex chemical processes yielding microcrystalline solids.