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Researchers Develop Designable Aluminum Molecular Rings

Aluminum is of particularly high natural abundance and application relevance (as zeolites like aluminosilicates and aluminophosphates et al.). The solution chemistry and cluster chemistry of Al(III) ions is an important basis for the study of the structure-activity relationship of alumina materials.

However, the fast hydrolysis of Al(III) ions greatly limit the acquisition of the accurate structure information of the intermediate states such as agglomeration. Therefore, the synthesis of aluminum oxide-clusters (AlOCs) with precise structure is a challenging task. 

A research group led by Prof. ZHANG Jian and Prof. FANG Weihui from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences, has successfully obtained a series of atomic precisely aluminum molecular rings. The study was published in Angew. Chem. Int. Ed.  

The researchers applied benzoate ligands to delay the hydrolysis process of Al(III) ions through coordinate bonds (denoted as CDH strategy) so as to promote crystallization and simultaneously enable condensation occurs. Ring molecular are commonly reported in transition metal or rare-earth compound systems, and such aluminum molecular rings with easily controlled structures is unprecedented. 

They found that the structure-directing agents of monohydric alcohols play an important role in the ring expansion. By changing the lengths of monohydric alcohols, the ring size of AlOCs was successfully tuned from 8-ring (Al8) to 16-ring (Al16) molecular ring architectures.

Moreover, the surface properties of these Al16 rings can be tuned from hydrophilicity to ultra-hydrophobicity through two kinds of methods. The first one is one-spot synthesis by using various benzoate derivatives (-F, -Cl, -NH2, -CH3). The other one is accomplished through the ligand substitution approach. 4-aminobenzoic acid bridged 16-ring (AlOC-12) is soluble in organic solvents and exhibits high solution stability revealed by electrospray ionization mass spectrometry (ESI-MS). By dissolving the AlOC-12 in the solvent and adding benzoate ligand, the surface properties transformation from hydrophilicity to ultra-hydrophobicity was realized. Such ligand substitution also achieved by benzoate derivatives such as p-methylbenzoic acid.

This study not only provides coordination delayed hydrolysis strategy toward the synthesis of crystalline Al(III)-based materials but also establishes a new platform to tune the chemical-property and subsequent utilization of these promising Al-rings.

 

Systematic expansion of aluminum rings by different monohydric alcohols (Image by Prof. ZHANG’s group) 

  

Contact:  

Prof. ZHANG Jian 

Fujian Institute of Research on the Structure of Matter  

Chinese Academy of Sciences  

Email: zhj@fjirsm.ac.cn 

  

  

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