Pathway selection in the self-assembly of Rh₄L₄ coordination squares under kinetic control

Area of Science:

• Supramolecular Chemistry
• Chemical Self-Assembly
• Coordination Chemistry

Background:

• Establishing pathway selection principles in reversible reaction networks, like molecular self-assembly, remains challenging.
• Kinetic control in reversible systems is more complex than in irreversible ones.
• Understanding self-assembly pathways is crucial for designing complex molecular architectures.

Purpose of the Study:

• To investigate kinetic control in the self-assembly of coordination squares and triangles.
• To elucidate the role of a leaving ligand in directing self-assembly pathways.
• To explore the formation of higher-order structures from self-assembled components.

Main Methods:

• Utilized cis-protected dinuclear rhodium(II) corner complexes and linear ditopic ligands for self-assembly.
• Employed a weak monotopic carboxylate ligand (2,6-dichlorobenzoate, dcb-) as a leaving ligand.
• Combined experimental techniques with numerical approaches to analyze the self-assembly pathway.
• Characterized the resulting structures using nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray analysis.

Main Results:

• Achieved kinetic control, selectively forming coordination squares and preventing triangle formation.
• Identified that the dcb- ligand blocks the cyclization step leading to triangular complexes.
• Observed the formation of a dimeric structure from one of the molecular squares due to solvophobic effects.

Conclusions:

• Demonstrated a method for achieving kinetic control in reversible self-assembly systems.
• Showcased the ability to selectively form molecular squares by modulating energy landscapes with a leaving ligand.
• Highlighted the influence of solvophobic effects on the assembly of supramolecular structures.