Designable Aluminum Molecular Rings: Ring Expansion and Ligand Functionalization

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Cyclic coordination compounds are well-established for transition metals, gallium, and lanthanides.
• Aluminum(III) molecular rings are less developed due to the inherent hydrolysis instability of the Al3+ ion.
• Developing stable and tunable Al(III) architectures is crucial for novel material applications.

Purpose of the Study:

• To synthesize and characterize atomic precisely Al(III) molecular rings with varying sizes (8-ring to 16-ring).
• To investigate the structure-directing role of monohydric alcohols in ring expansion.
• To explore the modification of ligand properties and achieve tunable surface characteristics.

Main Methods:

• Synthesis of Al(III) molecular rings using benzoate ligands and monohydric alcohols.
• Utilizing monohydric alcohols as structure-directing agents for controlled ring expansion.
• Characterization of Al(III) rings, including ligand modification and stability studies using mass spectroscopy.

Main Results:

• Successfully synthesized Al(III) molecular rings ranging from 8-ring to 16-ring architectures.
• Demonstrated that monohydric alcohol structure-directing agents control ring expansion.
• Achieved tunable surface properties (hydrophilicity to ultra-hydrophobicity) by modifying benzoate ligands.
• A 16-ring with 4-aminobenzoic acid ligands showed excellent solubility and solution stability.
• Demonstrated controllable ligand functionalization through ligand substitution reactions.

Conclusions:

• Monohydric alcohols are effective in directing the synthesis of precisely sized Al(III) molecular rings.
• Tunable surface properties and controllable functionalization of Al(III) rings are achievable.
• These stable and adaptable Al(III) molecular rings offer potential for advanced materials development.