Exploiting Reaction-Diffusion Conditions to Trigger Pathway Complexity in the Growth of a MOF.

Area of Science:

• Materials Science
• Chemical Engineering
• Crystallography

Background:

• Coordination polymers (CPs) and metal-organic frameworks (MOFs) are advanced crystalline materials with diverse applications.
• Understanding the formation mechanisms of CPs and MOFs is crucial for material design but remains largely unexplored.

Purpose of the Study:

• To investigate novel crystallization pathways for CPs, specifically a spin-crossover MOF.
• To explore the impact of controlled, rapid reagent mixing on MOF crystallization dynamics.

Main Methods:

• Utilized continuous-flow microfluidic devices for diffusion-controlled mixing of reagents within milliseconds (≈40 ms).
• Employed experimental observation and full-atom molecular dynamics simulations to analyze nucleation and growth pathways.
• Compared microfluidic mixing with traditional bulk (turbulent) mixing.

Main Results:

• Observed two distinct and unprecedented nucleation-growth pathways under microfluidic mixing conditions.
• Molecular dynamics simulations corroborated the occurrence of these pathways during crystal growth.
• Identified a crystallization-by-particle-attachment pathway under bulk mixing, contrasting with microfluidic results.

Conclusions:

• Demonstrated that rapid, diffusion-controlled mixing in microfluidics can steer MOF crystallization towards novel pathways and the thermodynamic product.
• Provided fundamental insights into CP growth mechanisms under out-of-equilibrium conditions.
• Opened new avenues for engineering porous materials through precise control of crystallization processes.