# Tandem mechanochemical engineering yields highly crystalline metal–organic frameworks

## TL;DR

A new mechanochemical method produces highly crystalline metal-organic frameworks by combining two reversible bond types, improving synthesis efficiency and crystallinity.

## Contribution

A tandem mechanochemical strategy using dual reversible bonds enhances MOF crystallinity and synthesis speed under ambient conditions.

## Key findings

- Tandem mechanochemistry with M–L and imine bonds enables rapid synthesis of crystalline MOFs.
- Irreversible bonds like ether or amide fail to produce quality MOFs under similar conditions.
- Dual reversible bonds improve crystallization kinetics in solid-state reactions.

## Abstract

The formation of highly crystalline metal–organic frameworks (MOFs) relies on reversible metal–ligand (M–L) bond formation under conditions that enable defect annealing. While solvothermal synthesis remains the most common method for producing crystalline MOFs, mechanochemical synthesis is emerging as a greener alternative. However, the solid-state nature of mechanochemical reactions—even when assisted by catalytic amounts of liquid additives—limits molecular mobility, thereby impeding defect annealing and crystallization. This work introduces a tandem mechanochemical engineering strategy to achieve highly crystalline MOFs by incorporating a second class of reversible bond formation—imine condensation—alongside traditional M–L coordination. The critical role of cooperative dynamics between M–L and imine reversible bonds is highlighted by systematic investigations using similar high-connectivity ligand analogues featuring irreversible covalent linkages (e.g., ether, amide, or alkyne), which fail to produce quality crystalline MOF phases under mechanochemical conditions. The synergistic effect of dual reversible bonds addresses sluggish reaction kinetics inherent to solid-state processes, enhances crystallization kinetics, and enables the efficient mechanochemical synthesis of MOFs with improved crystallinity under ambient conditions, particularly for frameworks constructed from high-connectivity ligands.

Tandem mechanochemical engineering, combining reversible M–L coordination and imine condensation, overcomes sluggish reaction kinetics and enables direct one-pot synthesis of highly crystalline MOFs in seconds.